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Changes in Wuchereria bancrofti infection in a highly endemic community following 10 rounds of mass administration of diethylcarbamazine
Transactions of the Royal Society of Tropical Medicine and Hygiene (2007) 101, 250—255
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Changes in Wuchereria bancrofti infection in a highly endemic community following 10 rounds of mass administration of diethylcarbamazine K.D. Ramaiah ∗, P. Vanamail, P.K. Das Vector Control Research Centre (Indian Council of Medical Research), Medical Complex, Indira Nagar, Pondicherry 605006, India Received 4 January 2006; received in revised form 9 May 2006; accepted 9 May 2006 Available online 4 August 2006
KEYWORDS Lymphatic filariasis; Diethylcarbamazine; Mass drug administration; Circulating filarial antigen; India
Summary Mass drug administration (MDA) is the principal strategy of the programme to eliminate lymphatic filariasis (LF). Evaluation of MDA in highly endemic ‘sentinel’ communities is necessary to understand its impact on LF infection. This study examined the changes in Wuchereria bancrofti infection following 10 rounds of annual mass administration of diethylcarbamazine (DEC) in a highly endemic community. The mean number of DEC treatments received per adult in the community was 7.4 ± 2.0. Following 10 rounds of DEC administration, the number of microfilaria (mf) carriers fell from 565 to 55. None of the pre-MDA amicrofilaraemic individuals showed circulating filarial antigen (CFA). However, 54.5% of the pre-MDA microfilaraemic individuals were positive for CFA. All the pre-MDA high intensity mf carriers continued to be positive for CFA, and some of them also showed blood mf. These patients are the most difficult to be cured by MDA and were distributed in 8.2% of the households. All the children born during the last 7 years of the MDA programme were negative for CFA. The study suggests that six to seven DEC treatments per individual suppresses microfilaraemia, except in some people with heavy infection, and repeated MDA has very good potential to prevent infection in children. © 2006 Royal Society of Tropical Medicine and Hygiene. Published by Elsevier Ltd. All rights reserved.
1. Introduction Lymphatic filariasis (LF) is targeted for elimination. Annual single-dose mass administration of diethylcarbamazine (DEC) or ivermectin combined with albendazole to endemic communities is the principal strategy of the global programme to eliminate LF (GPELF). Mass drug administration ∗
Corresponding author. Tel.: +91 413 2272396/2272422; fax: +91 413 2272041. E-mail address: [email protected] (K.D. Ramaiah).
(MDA) is evolving into a huge campaign against LF (WHO, 2005a). Such an MDA campaign requires robust monitoring and evaluation to understand the effectiveness and intricacies of LF elimination. Detailed monitoring and evaluation guidelines envisage assessment of prevalence of microfilaria (mf) in the community and antigenaemia in children 2—4 years of age, after four rounds of MDA, in sentinel and spotcheck sites in each intervention unit (WHO, 2005b). The sentinel sites need to be highly endemic, as the changes in microfilaraemia and antigenaemia prevalence in these sites reflect better the overall performance of the MDA programme.
0035-9203/$ — see front matter © 2006 Royal Society of Tropical Medicine and Hygiene. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.trstmh.2006.05.007
Yearly MDA of DEC and Wuchereria bancrofti infection The impact of mass administration of various drugs on microfilaraemia and antigenaemia at community level was assessed in different situations. These include assessment of DEC mass administration in Egypt (Ramzy et al., 2002) and India (Ramaiah et al., 2002, 2003a) with Culex species as vectors, DEC and DEC + ivermectin in Papua New Guinea (Bockarie et al., 2002) with Anopheles vectors, and DEC and/or DEC + albendazole in India (Rajendran et al., 2004) and Anopheles vector areas of Vanuatu (Fraser et al., 2005). These assessments were primarily based on cross-sectional mf and antigenaemia surveys. While they provide valuable information on changes in prevalence of community microfilaraemia and antigenaemia after various rounds of MDA, more in-depth information on such changes at individual and household level may enhance our understanding of the effectiveness of MDA. Also, the effectiveness of MDA was shown to be less in highly endemic villages compared with low endemic villages (Bockarie et al., 2002; Ramaiah et al., 2002, 2003b). Therefore, further investigations are imperative to understand the reasons for persistence of infection in highly endemic sites. DEC and ivermectin are the principal antifilarial drugs. Although, under the GPELF programme, WHO recommends mass administration of DEC or ivermectin combined with albendazole, at present the programme in India is using DEC alone in a vast majority of endemic districts and has introduced DEC + albendazole treatment on a pilot scale in a few districts. We have been studying the potential of annual DEC and ivermectin mass administration to eliminate Culextransmitted bancroftian filariasis in the villages of Villupuram district in Tamil Nadu, India (Das et al., 2001; Ramaiah et al., 2002, 2003b). These studies showed that four to six rounds of mass DEC administration, with 54—75% treatment coverage, has the potential to significantly reduce the mf prevalence and transmission potential but is not sufficient to totally interrupt transmission and eliminate LF. Hence, we implemented four more rounds of mass DEC administration in the study villages. One of the villages, Alagramam, had a pre-MDA mf rate of 17.2% and a vector infection rate of 29.2%, and these rates are among the highest observed in India. The epidemiological situation of the village represents that of a sentinel site (WHO, 2005b). In this village, after 10 cycles of mass DEC treatment, we have studied the prevalence of mf in cross-sectional and cohort surveys and antigenaemia in cohorts of adults and children born during the mass treatment period. The cohorts of adults included pre-intervention amicrofilaraemic asymptomatic individuals and microfilaraemic individuals with different intensities of infection. Assessment of their current status of microfilaraemia and antigenaemia provided an insight into the microfilaricidal and macrofilaricidal effects of DEC in relation to varying intensities of infection and number of treatments at individual and household level and prospects of elimination of Wuchereria bancrofti infection in a ‘sentinel’ highly endemic community.
1.1. Study village The study village, Alagramam, is located in Villupuram district in Tamil Nadu state in India. It is a large village, with a population of 3279, according to the census carried out in 1994. Historically, it is a highly endemic village
251 with an estimated 330 hydrocele patients and 210 lymphoedema patients. The annual biting rate of Culex quinquefasciatus, the vector of W. bancrofti, was estimated to be more than 20 000 during many years of the MDA period (1994—2004). The major occupation of the population is agriculture. Groups of people often go to other villages and towns for 2—3 months for employment. Permanent migration for employment in urban areas is not uncommon. No specific antifilariasis measures were implemented in the village before this study.
2. Materials and methods 2.1. Mass drug administration Under a research study sponsored by WHO and The Special Programme for Research and Training in Tropical Diseases (TDR), mass single-dose DEC administration had been initiated in the study village in 1994 to evaluate its potential to eliminate LF. The study was reviewed and approved by the institutional ethical committee. A total of 10 rounds of mass DEC administration was implemented in the village during 1994—2004. The first administration was carried out in November 1994 and the second 6 months later, and the subsequent eight rounds at 12—15 month intervals. Before the first MDA, the village population was enumerated and the weight of every individual was recorded. DEC was administered at the dose of 6 mg/kg body weight. Teams of health workers visited every household and directly administered the DEC tablets to the eligible people. Children under 15 kg body weight, pregnant women, the very old and people with serious illnesses were excluded from MDA (Ramaiah et al., 2002). Longitudinal DEC treatment details during 10 rounds of MDA for every individual were recorded and maintained. Such data for the children born during the MDA period were not available. For children positive for antigenaemia in the present study and eligible for treatment, the treatment details were collected by interviewing their parents.
2.2. Cross-sectional night blood surveys Before each round of MDA and 1 year after the tenth round, night blood surveys were carried out to assess the impact of MDA on mf prevalence. For each survey, 7% of the households were randomly selected and all the available members of the households were blood sampled. Sixty cmm of fingerprick blood was collected from each individual and made into three thick smears of 20 cmm each. The blood samples were processed in the laboratory the next morning and examined for mf. The number of mf for each positive person was recorded (Ramaiah et al., 2002).
2.3. Immunochromatography card test We used the immunochromatography (ICT) card test, following the instructions given by the manufacturer, to assess the circulating filarial antigen (CFA) prevalence in the study subjects. The CFA prevalence was assessed 1 year after the tenth MDA. ICT kits were procured from Binax, Portland, ME, USA. A cohort of pre-MDA asymptomatic amicrofilaraemic and microfilaraemic individuals and the children born after
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the initiation of MDA were tested for CFA. While the pre-MDA amicrofilaraemic individuals and the children were selected randomly, all the available pre-MDA microfilaraemic individuals detected from the sampled population were assessed for CFA. The individuals found positive for CFA were further tested for blood mf, following the procedure given in section 2.2 (above). Oral Informed consent was obtained from study participants. All the detected mf carriers and CFA-positive people during the study period were treated, on ethical grounds, with DEC at the dose of 6 mg/kg body weight.
3. Results Before MDA, a total of 238 individuals (111 males and 127 females) living in 73 households were surveyed to assess the mf prevalence in the study village. Of the 238 surveyed, 41 (18 males and 23 females) living in 26 households were found positive for mf. Thus, 17.2% of the surveyed people distributed in 35.6% of the households were microfilaraemic. Twenty-two per cent of the households were with one mf carrier and 13.6% with two to four. The arithmetic mean mf count of the carriers in households with one, two, three and four mf carriers was 176 ± 219, 185 ± 265, 235 ± 356 and 16 ± 10, respectively, and the average was 176 ± 257. The proportion of the households with mf carriers and the number of mf carriers in the community declined gradually with the progress of mass DEC administration. After the tenth MDA, 231 individuals (116 males and 115 females) living in 68 households were surveyed and only four (three males, one female) of them (1.7%) were found positive for mf (Table 1). They were found in four different households and in differ-
ent streets of the village. Their individual mf count was 1, 2, 96 and 113 and the arithmetic mean was 53 ± 60. Post-tenth MDA, there was only one mf carrier per 17.0 households, compared with one per 1.8 households before MDA. The decline in mf rate from pre-MDA to the post-tenth MDA period was 90%. One year after the tenth MDA, we assessed the CFA prevalence in 101 individuals (47 males and 54 females). They included four groups: (1) a cohort of 35 pre-MDA amicrofilaraemic asymptomatic individuals; (2) a cohort of 22 pre-MDA microfilaraemic asymptomatic individuals; (3) 24 children 2—5 years of age; and (4) 20 children 6—10 years of age. Individuals in groups 1 and 2 received an average of 7.5 ± 2.0 and 7.3 ± 2.1 treatments, respectively. Children in groups 3 and 4 were born after the initiation of MDA. While children in group 3 were excluded from treatment, treatment details for children in group 4 were not available, except for those positive for CFA. Out of 41 mf carriers detected before MDA (Table 1), only 22 were sampled in this study (group 2); the other 19 could not be sampled as they had either migrated or married into other villages and three individuals died. All the 35 individuals in group 1 were negative for CFA. Ten out of 22 (45.5%) individuals were CFA-positive in group 2 (Table 2). In this group, the CFA prevalence increased with pre-MDA mf intensity and four out of four in the highest mf intensity group were positive for CFA (Table 3). While all the children of group 3 were negative for CFA, three out of 20 children (15.0%) were positive in group 4. The three CFA positive children were 8—10 years old. The households of two CFA-positive children had two more mf carriers each before MDA. Two of the three CFA-positive children did not take treatment and one child underwent two treatments.
Table 1 Number of households and individuals sampled and proportion positive for microfilaria (mf) following different rounds of mass administration of diethylcarbamazine Study period
No. households sampled
No. (%) households with mf carriers
No. individuals sampled
No. (%) +ve for mf
Pre-MDA Post-II MDA Post-IV MDA Post-VI MDA Post-VIII MDA Post-X MDA
73 67 66 66 73 68
26 (35.6) 27 (40.3) 22 (33.3) 9 (13.6) 9 (12.3) 4 (5.9)
238 230 230 241 233 231
41 (17.2) 33 (14.3) 28 (12.2) 10 (4.1) 9 (3.9) 4 (1.7)
MDA: mass drug administration.
Table 2 Number of treatments of diethylcarbamazine received and circulating filarial antigen (CFA) and microfilaria (mf) prevalence in different categories of individuals Group
Category
No. sampled for CFA
Median age (range) [years]
Mean no. treatments ± SD
No. (%) +ve for CFA
No. (%) +ve for mfb
1 2 3 4
Pre-MDA mf − ve individuals Pre-MDA mf + ve individuals 2—5-year-old children 6—10-year-old children
35 22 24 20
38 (15—82) 42 (19—73) 4 (2—5) 8 (6—10)
7.5 ± 2.0 7.3 ± 2.1 0
0 10 (45.5) 0 3 (15.0)
— 2 (9.1) — 1 (5.0)
a
MDA: mass drug administration. a Data collected only for CFA-positive children; two children did not take treatment and one child took two treatments. b Blood examination for mf was done only in CFA + ve individuals.
Yearly MDA of DEC and Wuchereria bancrofti infection
253
Table 3 Number of treatments of diethylcarbamazine received and clearance of circulating filarial antigen (CFA) and microfilaraemia in individuals with different microfiliaria (mf) intensities Mf intensitya
Mean mf count (range)
No. sampled
Median age (range) [years]
Mean no. treatments ± SD
No. (%) +ve for CFA
No. (%) +ve for mf
Low Medium High
18.4 (2—36) 173.3 (60—300) 756.0 (408—935)
11 7 4
41 (19—73) 38 (19—70) 45 (40—61)
7.4 ± 2.1 7.7 ± 2.6 6.3 ± 1.0
3 (27.3) 3 (42.9) 4 (100.0)
1 (9.1) 0 (0.0) 2 (50.0)
a
Classification is relative to the mf intensity found in the study subjects.
Among the 13 CFA-positive individuals (10 adults, three children), four (three adults and one child) were also found positive for blood mf (Table 2). The three adult mf carriers had the pre-MDA mf intensity of 935, 930 and 31 mf per 60 cmm of blood and received six, seven and nine treatments, respectively. Their post-MDA mf intensity was 32, 15 and 2. The mf-positive child was a 10-year-old female, and her mf count was 10. Two more members of the child’s family had microfilaraemia before MDA, and the mf count of one of them was 930 per 60 cmm blood.
4. Discussion After 10 rounds of mass DEC administration, despite 90% reduction, 1.7% of the sampled population was positive for mf in 60 cmm thick blood films. At 1.7% mf prevalence, the expected number of mf carriers, detectable in 60 cmm thick blood films, in the study community is about 55. Farid et al. (2003) showed that the microfilaraemia level that is detectable in thick films of about 50 l blood is not safe from a transmission perspective. The presence of >50 such mf carriers in the study community suggests their potential to perpetuate transmission. Many studies have examined the clearance pattern of antigenaemia and microfilaraemia following DEC treatment given over a short period, of a few days to 18 months (Eberhard et al., 1997; Freedman et al., 2001; Ismail et al., 1996; Kazura et al., 1993; McCarthy et al., 1995; Nicolas et al., 1997; Pani et al., 2002; Ramzy et al., 2002; Schuetz et al., 2000; Weil et al., 1988). Most of these studies indicate that the impact of DEC treatment is very dramatic on mf, but only moderate on CFA. This study highlights the clearance of antigenaemia and microfilaraemia following repeated annual DEC mass treatment, over a 10-year period. In typical endemic situations, >10% of an amicrofilaraemic asymptomatic population shows CFA (Pani et al., 2000; Weil et al., 1996), a marker of adult worm infection (Chanteau et al., 1994). Its amicrofilaraemia status is due to low adult worm burden (Weil et al., 1996). In this study, after receiving 7.5 ± 2.0 treatments, none of the preMDA amicrofilaraemic individuals showed CFA (Table 2). This suggests that repeated annual DEC mass treatment may be able to clear and/or prevent infection in an amicrofilaraemic endemic population. This, however, needs further confirmation, as the pre-MDA CFA status of this population is not known in this study. Following 7.3 ± 2.1 treatments, 54.5% of the pre-MDA mf carriers turned CFA-negative (Table 2). The proportion of the mf carriers turning CFA-negative decreased with the increase in pre-MDA mf intensity. None of the four high-
intensity mf carriers turned CFA-negative, compared with 72.7 and 57.1% among low- and medium-intensity mf carriers, respectively (Table 3). Although the high-intensity mf carriers received about one treatment less than the other two categories, this difference alone does not explain the prevalence of CFA in all four of them. Besides, two of the four mf carriers continue to be microfilaraemic, suggesting the presence of reproductively active adult worms in them. Mf intensity indicates the adult worm burden (Hairston and Jachowski, 1968). Increase in clearance of CFA with decrease in mf intensity indicates that the macrofilaricidal effect of annual DEC treatment is higher in people with lighter adult worm burden than in people with heavy burden. In a recent study in Tanzania, 75.7% of pre-treatment mf carriers and 40.5% of mf-negative individuals showed CFA after seven to eight half-yearly DEC treatments (Simonsen et al., 2005). These proportions are lower at 45.5 and 0%, respectively, in this study. This may be due to the 10-year duration of MDA in this study compared with 4 years in the Tanzanian study. The natural death of adult worms, besides the macrofilaricidal effect of DEC, is expected to be higher over a 10-year period, although we do not know the proportion of adult worms that die due to the effect of the drug and natural reasons during and after MDA. Therefore, MDA at annual intervals may be more advantageous than at half-yearly intervals. Although 27.3 and 42.9% of the pre-MDA low- and medium-intensity mf carriers, respectively, showed CFA (Table 3), indicating adult worm presence, all of them except one were found to be amicrofilaraemic and are currently less important from a transmission perspective. Their becoming microfilaraemic in future and causing transmission depends upon the reproductive potential of the adult worms in them. The annual transmission potential (ATP) in the study community was 2690 before mass DEC administration, 852 and 1576 during the initial two rounds of MDA, and 50 to 237 during the third to sixth round of MDA (Ramaiah et al., 2003b), and the number of infective mosquitoes showed a further declining trend during the seventh to tenth MDA (K.D. Ramaiah, unpublished data). Hence, most of the surviving adult worms in this category of individuals might have resulted from infection acquired before the third MDA, when the ATP was substantial. These worms are more than 8—9 years old, near to the upper limit of the life span (Leeuwin, 1962; Subramanian et al., 2004; Vanamail et al., 1990). ATP during some years after the third MDA was also more than 100, the estimated safe level (Ramaiah et al., 1994). Hence, a smaller proportion of adult worms might have resulted from infection acquired after the third MDA. These worms, although less than 8—9 years old, were exposed to treatment over an eight-year period. Simonsen et al. (2005) reported a 94% reduction, after seven to eight DEC treatments, in
254 intensity of CFA in pre-MDA mf carriers, suggesting that the adult worm load in these individuals is very meagre and may gradually diminish. Persistence of microfilaraemia in two of the four pre-MDA high-intensity mf carriers, even after 6.3 ± 1.0 treatments (Table 3), indicates that the risk of microfilaraemic individuals remaining microfilaraemic (Meyrowitsch et al., 2004) is higher in high-intensity mf carriers. This, however, requires further confirmation, as we were able to include only four high-intensity mf carriers in this study. Also, the households of both the persistent mf carriers contained at least one more mf carrier before MDA, suggesting more intense transmission within these households. This, combined with slow clearance of infection in this category of individuals (Table 3), necessitates more treatments to cure infection in high-intensity mf carriers and their household members. They constituted 1.8% of the population and 14.6% of the total mf carriers and were distributed in 8.2% of the households in the village before MDA. No feasible techniques are available to detect these households to give intensive treatment to their members. Therefore, it may be necessary to continue mass DEC treatment beyond 10 rounds, until the mf rate is reduced to <1% (WHO, 2005b) and mf intensity is at a safe level in these communities. Absence of CFA in preMDA amicrofilaraemic individuals (Table 2), persistence of CFA as well as microfilaraemia in high-intensity mf carriers and decreased clearance of CFA with increase in mf intensity suggest that clearance of CFA (Table 3), an indication of macrofilaricidal effect of annual DEC treatment, is more related to pre-treatment adult worm burden. By contrast to the highly endemic large villages, control/elimination of LF may be less difficult and possible with four to eight rounds of mass DEC administration in low endemic and small villages in Culex vector areas (Ramaiah et al., 2002, 2003b), as the proportion and number of highdensity mf carriers is likely to be smaller. This necessitates differentiation of highly endemic villages from low endemic ones, using a criterion such as the number of chronic patients, as the number of MDAs required for both the category of villages is different. Although excluded from treatment, none of the children in the 2—5 years age group (mean body weight <15 kg) was CFA-positive in this study, compared with a 22.2% positive rate after six rounds of MDA (Ramaiah et al., 2003a). The youngest CFA-positive child was 8 years old, suggesting that no new infections occurred during the last 7 years of MDA. Only one child, 10 years of age, was positive for both CFA and mf, and her household had two more mf carriers before MDA — one with a high count of 930 mf. This finding re-emphasizes the risk posed by the households with high intensity and multiple mf carriers to cause transmission and new infections. Occurrence of CFA in 8—10-year-old children (Table 2) is not surprising, because they were born before the third MDA, when substantial transmission occurred, and were included for treatment only after they became 5 years of age (mean body weight 15 kg) and received only a few or no treatments (Table 2). This study showed that DEC exerts a better macrofilaricidal effect in low-intensity mf carriers. The prevalence and intensity of infection in children are generally low (Stolk et al., 2004) and hence are expected to be more amenable to DEC treatment. The inclusion of children in MDA from the age of 2 years, as envisaged by the GPELF, and from
K.D. Ramaiah et al. the very initial rounds of MDA is important to prevent new infections and protect the children from subsequent clinical consequences (Witt and Ottesen, 2001). Existence of risk of transmission during the initial rounds of MDA also highlights the fact that monitoring and evaluation of children born during this period will yield more robust information on the impact of MDA. The treatment coverage of 55 to 75%, observed in the present study village, is similar to that observed in many LF elimination programmes (Babu and Kar, 2004; de Rochars et al., 2005; Ramaiah et al., 2000) but is less than the effective treatment coverage of 80%. Effective treatment coverage may yield better results than those reported in this study. We conclude that six to seven DEC treatments per individual have the potential to totally suppress micfofilaraemia in all individuals, except in some of those with heavy infection. Slightly less than half of the pre-MDA mf carriers continue to be positive for CFA, but a vast majority of them turned amicrofilaraemic. More follow-up studies in highly endemic villages may be necessary to understand the course of infection in individuals with high intensities of infection and the prospects of elimination of LF. Conflicts of interest statement The authors have no conflicts of interest concerning the work reported in this paper.
Acknowledgements We express our gratitude to the villagers of Alagramam for their co-operation and participation in the study. We are thankful to Mr Bashir Ahmed and Mr S.B. Chakravarthy, Vector Control Research Centre (VCRC), Pondicherry, for their help in collecting and processing the blood films and carrying out ICT card tests. Our thanks are due to Dr S. Subramanian, VCRC, for his critical remarks on the manuscript. We thank Drs Hans Remme, Gautam Biswas, Boatin and Kumaraswamy for their constant support to the study team. Part of the study received financial support from UNDP/World Bank/WHO/TDR under the grant no. 920702.
References Babu, B.V., Kar, S.K., 2004. Coverage, compliance and some operational issues of mass drug administration during the programme to eliminate lymphatic filariasis in Orissa, India. Trop. Med. Int. Health 9, 702—709. Bockarie, M.J., Tisch, D.J., Kastens, W., Alexander, N.D., Dimber, Z., Bockarie, F., Ibam, E., Alpers, M.P., Kazura, J.W., 2002. Mass treatment to eliminate filariasis in Papua New Guinea. N. Eng. J. Med. 23, 1841—1848. Chanteau, S., Moulia-Pelat, J.P., Glaziou, P., Nguyen, N.L., Luquiaud, P., Plichart, C., Martin, P.M.V., Cartel, J.L., 1994. Og4C3 circulating antigen: a marker of infection and adult worm burden in Wuchereria bancrofti filariasis. J. Infect. Dis. 120, 247—250. Das, P.K., Ramaiah, K.D., Vanamail, P., Pani, S.P., Yuvaraj, J., Balarajan, K., Bundy, D.A.P., 2001. Placebo-controlled community trial of four cycles of single-dose diethylcarbamazine or ivermectin against Wuchereria bancrofti infection and transmission in India. Trans. R. Soc. Trop. Med. Hyg. 95, 336—341. de Rochars, M.B., Kanjilal, S., Direny, A.N., Radday, J., Lafontant, J.G., Mathieu, E., Rheingans, R.D., Haddix, A.C., Streit, T.G.,
Yearly MDA of DEC and Wuchereria bancrofti infection Beach, M.J., Addiss, D.G., Lammie, P.J., 2005. The Leogane, Haiti demonstration project: decreased microfilaremia and program costs after three years of mass drug administration. Am. J. Trop. Med. Hyg. 73, 888—894. Eberhard, M.L., Hightower, A.W., Addiss, D.G., Lammie, P.J., 1997. Clearance of Wuchereria bancrofti antigen after treatment with diethylcarbamazine or ivermectin. Am. J. Trop. Med. Hyg. 57, 483—486. Farid, H.A., Hammad, R.E., Soliman, D.A., El Setouhy, M., Ramzy, R.M.R., Weil, G.J., 2003. Relationships between Wuchereria bancrofti microfilaraemia in human blood and parasite uptake and maturation in Culex pipiens, with observations on the effect of diethylcarbamazine treatment on these parameters. Am. J. Trop. Med. Hyg. 68, 286—293. Fraser, M., Taleo, G., Taleo, F., Yaviong, J., Amos, M., Babu, M., Kalkoa, M., 2005. Evaluation of the program to eliminate lymphatic filariasis in Vanuatu following two years of mass drug administration implementation: results and methodologic approach. Am. J. Trop. Med. Hyg. 73, 753—758. Freedman, D.O., Plier, D.A., de Almeida, A.B., de Oliveira, A.L., Miranda, J., Braga, C., 2001. Effect of aggressive prolonged diethylcarbamazine therapy on circulating antigen levels in bancroftian filariasis. Trop. Med. Int. Health 6, 37—41. Hairston, N.G., Jachowski, L.A., 1968. Analysis of the Wuchereria bancrofti population in the people of American Samoa. Bull. World Health Organ. 38, 29—59. Ismail, M.M., Weil, G.J., Jayasinghe, K.S.A., Premaratne, U.N., Abeyewickreme, W., Rajaratnam, H.N., Sheriff, H.R., Perera, C.S., Dissanaike, A.S., 1996. Prolonged clearance of microfilaraemia in patients with bancroftian filariasis after multiple high doses of ivermectin or diethylcarbamazine. Trans. R. Soc. Trop. Med. Hyg. 90, 684—688. Kazura, J., Greenberg, J., Perry, R., Weil, G.J., Day, K., Alpers, M., 1993. Comparison of single-dose diethylcarbamazine and ivermectin for treatment of bancroftian filariasis in Papua New Guinea. Am. J. Trop. Med. Hyg. 49, 804—811. Leeuwin, R.S., 1962. Microfilaraemia in Surinamese living in Amsterdam. Trop. Geogr. Med. 14, 355—360. McCarthy, J.S., Guinea, A., Weil, G.J., Ottesen, E.A., 1995. Clearance of circulating filarial antigen as a measure of the macrofilaricidal activity of diethylcarbamazine in Wuchereria bancrofti infection. J. Infect. Dis. 172, 521—526. Meyrowitsch, D.W., Simonsen, P.E., Magesa, S.M., 2004. Long-term effect of three different strategies for mass diethylcarbamazine administration in bancroftian filariasis: follow-up at 10 years after treatment. Trans. R. Soc. Trop. Med. Hyg. 98, 627—634. Nicolas, L., Plichart, C., Nguyen, L.N., Moulia-Pelat, J.P., 1997. Reduction of Wuchereria bancrofti adult worm circulating antigen after annual treatments of diethylcarbamazine combined with ivermectin in French Polynesia. J. Infect. Dis. 175, 489—492. Pani, S.P., Hoti, S.L., Elango, A., Yuvaraj, Y., Lal, R., Ramaiah, K.D., 2000. Evaluation of ICT whole blood antigen card test to detect infection due to nocturnally periodic Wuchereria bancrofti in south India. Trop. Med. Int. Health 5, 359—363. Pani, S.P., Subramaniam Reddy, G., Das, L.K., Vanamail, P., Hoti, S.L., Ramesh, J., Das, P.K., 2002. Tolerability and efficacy of single dose albendazole, Diethylcarbamazine citrate (DEC) or co-administration of albendazole with DEC in the clearance of Wuchereria bancrofti in asymptomatic microfilaraemic volunteers in Pondicherry, south India: a hospital based study. Filaria J. 1, 1—11. Rajendran, R., Sunish, I.P., Mani, T.R., Munirathinam, A., Abdullah, S.M., Arunachalam, N., Satyanarayana, K., 2004. Impact of two annual single-dose mass drug administrations with diethylcarbamazine alone or in combination with albendazole on Wuchereria bancrofti microfilaraemia and antigenaemia in south India. Trans. R. Soc. Trop. Med. Hyg. 98, 174—181.
255 Ramaiah, K.D., Das, P.K., Dhanda, V., 1994. Estimation of permissible levels of transmission of bancroftian filariasis based on some entomological and parasitological results of a 5-year vector control programme. Acta Trop. 56, 89—96. Ramaiah, K.D., Das, P.K., Appavoo, N.C., Ramu, K., Augustin, D.J., Vijay Kumar, K.N., Chandrakala, A.V., 2000. A programme to eliminate lymphatic filariasis in Tamil Nadu state, India: compliance with annual single dose DEC mass treatment and some related operational aspects. Trop. Med. Int. Health 5, 842—847. Ramaiah, K.D., Vanamail, P., Pani, S.P., Yuvaraj, J., Das, P.K., 2002. The effect of six rounds of single dose mass treatment with diethylcarbamazine or ivermectin on Wuchereria bancrofti infection and its implications for lymphatic filariasis elimination. Trop. Med. Int. Health 7, 767—774. Ramaiah, K.D., Vanamail, P., Pani, S.P., Yuvaraj, J., Das, P.K., 2003a. The prevalence of Wuchereria bancrofti antigenaemia in communities given six rounds treatment with diethylcarbamazine, ivermectin or placebo tablets. Ann. Trop. Med. Parasitol. 97, 737—741. Ramaiah, K.D., Vanamail, P., Pani, S.P., Yuvaraj, J., Das, P.K., 2003b. The impact of six rounds of single dose mass administration of diethylcarbamazine or ivermectin on the transmission of Wuchereria bancrofti by Culex quinquefasciatus. Trop. Med. Int. Health 8, 1—11. Ramzy, R.M., El Setouhy, M., Helmy, H., Kandil, A.M., Ahmed, E.S., Farid, H.A., Faris, R., Weil, G.J., 2002. The impact of singledose diethylcarbamazine treatment of bancroftian filariasis in a low-endemicity setting in Egypt. Am. J. Trop. Med. Hyg. 67, 196—200. Schuetz, A., Addiss, D.G., Eberhard, M.L., Lammie, P.J., 2000. Evaluation of the whole blood filariasis ICT test for short-term monitoring after antifilarial treatment. Am. J. Trop. Med. Hyg. 62, 502—503. Simonsen, P.E., Magesa, S.M., Meyrowitsch, D.W., Malecela-Lazaro, M.N., Rwegoshora, R.T., Jaoko, W.G., Michael, E., 2005. The effect of eight half-yearly single-dose treatments with DEC on Wuchereria bancrofti circulating antigenaemia. Trans. R. Soc. Trop. Med. Hyg. 99, 541—547. Stolk, W.A., Ramaiah, K.D., Van Oortmarssen, G.J., Das, P.K., Habbema, J.D.F., De Vlas, S.J., 2004. Meta-analysis of ageprevalence patterns in lymphatic filariasis: no decline in microfilaraemia prevalence in older age groups as predicted by models with acquired immunity. Parasitology 129, 605—612. Subramanian, S., Habbema, J.D.F., Ramaiah, K.D., Stolk, W.A., Krishnamoorthy, K., van Oortmarssen, G.J., Amalraj, D., Plaisier, A.P., Das, P.K., 2004. The dynamics of Wuchereria bancrofti infection: a model-based analysis of longitudinal data from Pondicherry, India. Parasitology 128, 467—482. Vanamail, P., Subramanian, S., Das, P.K., Pani, S.P., Rajagopalan, P.K., 1990. Estimation of fecundic life span of Wuchereria bancrofti from longitudinal study of human infection in an endemic area of Pondicherry (south India). Ind. J. Med. Res. 91, 293—297. Weil, G.J., Sethumadhavan, K.V., Santhanam, S., Jain, D.C., Ghosh, T.K., 1988. Persistence of parasite antigenaemia following diethylcarbamazine therapy of bancroftian filariasis. Am. J. Trop. Med. Hyg. 38, 589—595. Weil, G.J., Ramzy, R.M., Chandrashekar, R., Gad, A.M., Lowrie Jr., R.C., Faris, R., 1996. Parasite antigenemia without microfilaremia in bancroftian filariasis. Am. J. Trop. Med. Hyg. 55, 333—337. Witt, C., Ottesen, E.A., 2001. Lymphatic filariasis: an infection of childhood. Trop. Med. Int. Health 6, 582—606. WHO, 2005a. Global programme to eliminate lymphatic filariasis. Wkly Epidemiol. Rec. 80, 202—212. WHO, 2005b. Monitoring and epidemiological assessment of the programme to eliminate lymphatic filariasis at implementation unit level. World Health Organization, Geneva, WHO/CDS/CPE/CEE 2005.50.
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Changes in Wuchereria bancrofti infection in a highly endemic community following 10 rounds of mass administration of diethylcarbamazine K.D. Ramaiah ∗, P. Vanamail, P.K. Das Vector Control Research Centre (Indian Council of Medical Research), Medical Complex, Indira Nagar, Pondicherry 605006, India Received 4 January 2006; received in revised form 9 May 2006; accepted 9 May 2006 Available online 4 August 2006
KEYWORDS Lymphatic filariasis; Diethylcarbamazine; Mass drug administration; Circulating filarial antigen; India
Summary Mass drug administration (MDA) is the principal strategy of the programme to eliminate lymphatic filariasis (LF). Evaluation of MDA in highly endemic ‘sentinel’ communities is necessary to understand its impact on LF infection. This study examined the changes in Wuchereria bancrofti infection following 10 rounds of annual mass administration of diethylcarbamazine (DEC) in a highly endemic community. The mean number of DEC treatments received per adult in the community was 7.4 ± 2.0. Following 10 rounds of DEC administration, the number of microfilaria (mf) carriers fell from 565 to 55. None of the pre-MDA amicrofilaraemic individuals showed circulating filarial antigen (CFA). However, 54.5% of the pre-MDA microfilaraemic individuals were positive for CFA. All the pre-MDA high intensity mf carriers continued to be positive for CFA, and some of them also showed blood mf. These patients are the most difficult to be cured by MDA and were distributed in 8.2% of the households. All the children born during the last 7 years of the MDA programme were negative for CFA. The study suggests that six to seven DEC treatments per individual suppresses microfilaraemia, except in some people with heavy infection, and repeated MDA has very good potential to prevent infection in children. © 2006 Royal Society of Tropical Medicine and Hygiene. Published by Elsevier Ltd. All rights reserved.
1. Introduction Lymphatic filariasis (LF) is targeted for elimination. Annual single-dose mass administration of diethylcarbamazine (DEC) or ivermectin combined with albendazole to endemic communities is the principal strategy of the global programme to eliminate LF (GPELF). Mass drug administration ∗
Corresponding author. Tel.: +91 413 2272396/2272422; fax: +91 413 2272041. E-mail address: [email protected] (K.D. Ramaiah).
(MDA) is evolving into a huge campaign against LF (WHO, 2005a). Such an MDA campaign requires robust monitoring and evaluation to understand the effectiveness and intricacies of LF elimination. Detailed monitoring and evaluation guidelines envisage assessment of prevalence of microfilaria (mf) in the community and antigenaemia in children 2—4 years of age, after four rounds of MDA, in sentinel and spotcheck sites in each intervention unit (WHO, 2005b). The sentinel sites need to be highly endemic, as the changes in microfilaraemia and antigenaemia prevalence in these sites reflect better the overall performance of the MDA programme.
0035-9203/$ — see front matter © 2006 Royal Society of Tropical Medicine and Hygiene. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.trstmh.2006.05.007
Yearly MDA of DEC and Wuchereria bancrofti infection The impact of mass administration of various drugs on microfilaraemia and antigenaemia at community level was assessed in different situations. These include assessment of DEC mass administration in Egypt (Ramzy et al., 2002) and India (Ramaiah et al., 2002, 2003a) with Culex species as vectors, DEC and DEC + ivermectin in Papua New Guinea (Bockarie et al., 2002) with Anopheles vectors, and DEC and/or DEC + albendazole in India (Rajendran et al., 2004) and Anopheles vector areas of Vanuatu (Fraser et al., 2005). These assessments were primarily based on cross-sectional mf and antigenaemia surveys. While they provide valuable information on changes in prevalence of community microfilaraemia and antigenaemia after various rounds of MDA, more in-depth information on such changes at individual and household level may enhance our understanding of the effectiveness of MDA. Also, the effectiveness of MDA was shown to be less in highly endemic villages compared with low endemic villages (Bockarie et al., 2002; Ramaiah et al., 2002, 2003b). Therefore, further investigations are imperative to understand the reasons for persistence of infection in highly endemic sites. DEC and ivermectin are the principal antifilarial drugs. Although, under the GPELF programme, WHO recommends mass administration of DEC or ivermectin combined with albendazole, at present the programme in India is using DEC alone in a vast majority of endemic districts and has introduced DEC + albendazole treatment on a pilot scale in a few districts. We have been studying the potential of annual DEC and ivermectin mass administration to eliminate Culextransmitted bancroftian filariasis in the villages of Villupuram district in Tamil Nadu, India (Das et al., 2001; Ramaiah et al., 2002, 2003b). These studies showed that four to six rounds of mass DEC administration, with 54—75% treatment coverage, has the potential to significantly reduce the mf prevalence and transmission potential but is not sufficient to totally interrupt transmission and eliminate LF. Hence, we implemented four more rounds of mass DEC administration in the study villages. One of the villages, Alagramam, had a pre-MDA mf rate of 17.2% and a vector infection rate of 29.2%, and these rates are among the highest observed in India. The epidemiological situation of the village represents that of a sentinel site (WHO, 2005b). In this village, after 10 cycles of mass DEC treatment, we have studied the prevalence of mf in cross-sectional and cohort surveys and antigenaemia in cohorts of adults and children born during the mass treatment period. The cohorts of adults included pre-intervention amicrofilaraemic asymptomatic individuals and microfilaraemic individuals with different intensities of infection. Assessment of their current status of microfilaraemia and antigenaemia provided an insight into the microfilaricidal and macrofilaricidal effects of DEC in relation to varying intensities of infection and number of treatments at individual and household level and prospects of elimination of Wuchereria bancrofti infection in a ‘sentinel’ highly endemic community.
1.1. Study village The study village, Alagramam, is located in Villupuram district in Tamil Nadu state in India. It is a large village, with a population of 3279, according to the census carried out in 1994. Historically, it is a highly endemic village
251 with an estimated 330 hydrocele patients and 210 lymphoedema patients. The annual biting rate of Culex quinquefasciatus, the vector of W. bancrofti, was estimated to be more than 20 000 during many years of the MDA period (1994—2004). The major occupation of the population is agriculture. Groups of people often go to other villages and towns for 2—3 months for employment. Permanent migration for employment in urban areas is not uncommon. No specific antifilariasis measures were implemented in the village before this study.
2. Materials and methods 2.1. Mass drug administration Under a research study sponsored by WHO and The Special Programme for Research and Training in Tropical Diseases (TDR), mass single-dose DEC administration had been initiated in the study village in 1994 to evaluate its potential to eliminate LF. The study was reviewed and approved by the institutional ethical committee. A total of 10 rounds of mass DEC administration was implemented in the village during 1994—2004. The first administration was carried out in November 1994 and the second 6 months later, and the subsequent eight rounds at 12—15 month intervals. Before the first MDA, the village population was enumerated and the weight of every individual was recorded. DEC was administered at the dose of 6 mg/kg body weight. Teams of health workers visited every household and directly administered the DEC tablets to the eligible people. Children under 15 kg body weight, pregnant women, the very old and people with serious illnesses were excluded from MDA (Ramaiah et al., 2002). Longitudinal DEC treatment details during 10 rounds of MDA for every individual were recorded and maintained. Such data for the children born during the MDA period were not available. For children positive for antigenaemia in the present study and eligible for treatment, the treatment details were collected by interviewing their parents.
2.2. Cross-sectional night blood surveys Before each round of MDA and 1 year after the tenth round, night blood surveys were carried out to assess the impact of MDA on mf prevalence. For each survey, 7% of the households were randomly selected and all the available members of the households were blood sampled. Sixty cmm of fingerprick blood was collected from each individual and made into three thick smears of 20 cmm each. The blood samples were processed in the laboratory the next morning and examined for mf. The number of mf for each positive person was recorded (Ramaiah et al., 2002).
2.3. Immunochromatography card test We used the immunochromatography (ICT) card test, following the instructions given by the manufacturer, to assess the circulating filarial antigen (CFA) prevalence in the study subjects. The CFA prevalence was assessed 1 year after the tenth MDA. ICT kits were procured from Binax, Portland, ME, USA. A cohort of pre-MDA asymptomatic amicrofilaraemic and microfilaraemic individuals and the children born after
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the initiation of MDA were tested for CFA. While the pre-MDA amicrofilaraemic individuals and the children were selected randomly, all the available pre-MDA microfilaraemic individuals detected from the sampled population were assessed for CFA. The individuals found positive for CFA were further tested for blood mf, following the procedure given in section 2.2 (above). Oral Informed consent was obtained from study participants. All the detected mf carriers and CFA-positive people during the study period were treated, on ethical grounds, with DEC at the dose of 6 mg/kg body weight.
3. Results Before MDA, a total of 238 individuals (111 males and 127 females) living in 73 households were surveyed to assess the mf prevalence in the study village. Of the 238 surveyed, 41 (18 males and 23 females) living in 26 households were found positive for mf. Thus, 17.2% of the surveyed people distributed in 35.6% of the households were microfilaraemic. Twenty-two per cent of the households were with one mf carrier and 13.6% with two to four. The arithmetic mean mf count of the carriers in households with one, two, three and four mf carriers was 176 ± 219, 185 ± 265, 235 ± 356 and 16 ± 10, respectively, and the average was 176 ± 257. The proportion of the households with mf carriers and the number of mf carriers in the community declined gradually with the progress of mass DEC administration. After the tenth MDA, 231 individuals (116 males and 115 females) living in 68 households were surveyed and only four (three males, one female) of them (1.7%) were found positive for mf (Table 1). They were found in four different households and in differ-
ent streets of the village. Their individual mf count was 1, 2, 96 and 113 and the arithmetic mean was 53 ± 60. Post-tenth MDA, there was only one mf carrier per 17.0 households, compared with one per 1.8 households before MDA. The decline in mf rate from pre-MDA to the post-tenth MDA period was 90%. One year after the tenth MDA, we assessed the CFA prevalence in 101 individuals (47 males and 54 females). They included four groups: (1) a cohort of 35 pre-MDA amicrofilaraemic asymptomatic individuals; (2) a cohort of 22 pre-MDA microfilaraemic asymptomatic individuals; (3) 24 children 2—5 years of age; and (4) 20 children 6—10 years of age. Individuals in groups 1 and 2 received an average of 7.5 ± 2.0 and 7.3 ± 2.1 treatments, respectively. Children in groups 3 and 4 were born after the initiation of MDA. While children in group 3 were excluded from treatment, treatment details for children in group 4 were not available, except for those positive for CFA. Out of 41 mf carriers detected before MDA (Table 1), only 22 were sampled in this study (group 2); the other 19 could not be sampled as they had either migrated or married into other villages and three individuals died. All the 35 individuals in group 1 were negative for CFA. Ten out of 22 (45.5%) individuals were CFA-positive in group 2 (Table 2). In this group, the CFA prevalence increased with pre-MDA mf intensity and four out of four in the highest mf intensity group were positive for CFA (Table 3). While all the children of group 3 were negative for CFA, three out of 20 children (15.0%) were positive in group 4. The three CFA positive children were 8—10 years old. The households of two CFA-positive children had two more mf carriers each before MDA. Two of the three CFA-positive children did not take treatment and one child underwent two treatments.
Table 1 Number of households and individuals sampled and proportion positive for microfilaria (mf) following different rounds of mass administration of diethylcarbamazine Study period
No. households sampled
No. (%) households with mf carriers
No. individuals sampled
No. (%) +ve for mf
Pre-MDA Post-II MDA Post-IV MDA Post-VI MDA Post-VIII MDA Post-X MDA
73 67 66 66 73 68
26 (35.6) 27 (40.3) 22 (33.3) 9 (13.6) 9 (12.3) 4 (5.9)
238 230 230 241 233 231
41 (17.2) 33 (14.3) 28 (12.2) 10 (4.1) 9 (3.9) 4 (1.7)
MDA: mass drug administration.
Table 2 Number of treatments of diethylcarbamazine received and circulating filarial antigen (CFA) and microfilaria (mf) prevalence in different categories of individuals Group
Category
No. sampled for CFA
Median age (range) [years]
Mean no. treatments ± SD
No. (%) +ve for CFA
No. (%) +ve for mfb
1 2 3 4
Pre-MDA mf − ve individuals Pre-MDA mf + ve individuals 2—5-year-old children 6—10-year-old children
35 22 24 20
38 (15—82) 42 (19—73) 4 (2—5) 8 (6—10)
7.5 ± 2.0 7.3 ± 2.1 0
0 10 (45.5) 0 3 (15.0)
— 2 (9.1) — 1 (5.0)
a
MDA: mass drug administration. a Data collected only for CFA-positive children; two children did not take treatment and one child took two treatments. b Blood examination for mf was done only in CFA + ve individuals.
Yearly MDA of DEC and Wuchereria bancrofti infection
253
Table 3 Number of treatments of diethylcarbamazine received and clearance of circulating filarial antigen (CFA) and microfilaraemia in individuals with different microfiliaria (mf) intensities Mf intensitya
Mean mf count (range)
No. sampled
Median age (range) [years]
Mean no. treatments ± SD
No. (%) +ve for CFA
No. (%) +ve for mf
Low Medium High
18.4 (2—36) 173.3 (60—300) 756.0 (408—935)
11 7 4
41 (19—73) 38 (19—70) 45 (40—61)
7.4 ± 2.1 7.7 ± 2.6 6.3 ± 1.0
3 (27.3) 3 (42.9) 4 (100.0)
1 (9.1) 0 (0.0) 2 (50.0)
a
Classification is relative to the mf intensity found in the study subjects.
Among the 13 CFA-positive individuals (10 adults, three children), four (three adults and one child) were also found positive for blood mf (Table 2). The three adult mf carriers had the pre-MDA mf intensity of 935, 930 and 31 mf per 60 cmm of blood and received six, seven and nine treatments, respectively. Their post-MDA mf intensity was 32, 15 and 2. The mf-positive child was a 10-year-old female, and her mf count was 10. Two more members of the child’s family had microfilaraemia before MDA, and the mf count of one of them was 930 per 60 cmm blood.
4. Discussion After 10 rounds of mass DEC administration, despite 90% reduction, 1.7% of the sampled population was positive for mf in 60 cmm thick blood films. At 1.7% mf prevalence, the expected number of mf carriers, detectable in 60 cmm thick blood films, in the study community is about 55. Farid et al. (2003) showed that the microfilaraemia level that is detectable in thick films of about 50 l blood is not safe from a transmission perspective. The presence of >50 such mf carriers in the study community suggests their potential to perpetuate transmission. Many studies have examined the clearance pattern of antigenaemia and microfilaraemia following DEC treatment given over a short period, of a few days to 18 months (Eberhard et al., 1997; Freedman et al., 2001; Ismail et al., 1996; Kazura et al., 1993; McCarthy et al., 1995; Nicolas et al., 1997; Pani et al., 2002; Ramzy et al., 2002; Schuetz et al., 2000; Weil et al., 1988). Most of these studies indicate that the impact of DEC treatment is very dramatic on mf, but only moderate on CFA. This study highlights the clearance of antigenaemia and microfilaraemia following repeated annual DEC mass treatment, over a 10-year period. In typical endemic situations, >10% of an amicrofilaraemic asymptomatic population shows CFA (Pani et al., 2000; Weil et al., 1996), a marker of adult worm infection (Chanteau et al., 1994). Its amicrofilaraemia status is due to low adult worm burden (Weil et al., 1996). In this study, after receiving 7.5 ± 2.0 treatments, none of the preMDA amicrofilaraemic individuals showed CFA (Table 2). This suggests that repeated annual DEC mass treatment may be able to clear and/or prevent infection in an amicrofilaraemic endemic population. This, however, needs further confirmation, as the pre-MDA CFA status of this population is not known in this study. Following 7.3 ± 2.1 treatments, 54.5% of the pre-MDA mf carriers turned CFA-negative (Table 2). The proportion of the mf carriers turning CFA-negative decreased with the increase in pre-MDA mf intensity. None of the four high-
intensity mf carriers turned CFA-negative, compared with 72.7 and 57.1% among low- and medium-intensity mf carriers, respectively (Table 3). Although the high-intensity mf carriers received about one treatment less than the other two categories, this difference alone does not explain the prevalence of CFA in all four of them. Besides, two of the four mf carriers continue to be microfilaraemic, suggesting the presence of reproductively active adult worms in them. Mf intensity indicates the adult worm burden (Hairston and Jachowski, 1968). Increase in clearance of CFA with decrease in mf intensity indicates that the macrofilaricidal effect of annual DEC treatment is higher in people with lighter adult worm burden than in people with heavy burden. In a recent study in Tanzania, 75.7% of pre-treatment mf carriers and 40.5% of mf-negative individuals showed CFA after seven to eight half-yearly DEC treatments (Simonsen et al., 2005). These proportions are lower at 45.5 and 0%, respectively, in this study. This may be due to the 10-year duration of MDA in this study compared with 4 years in the Tanzanian study. The natural death of adult worms, besides the macrofilaricidal effect of DEC, is expected to be higher over a 10-year period, although we do not know the proportion of adult worms that die due to the effect of the drug and natural reasons during and after MDA. Therefore, MDA at annual intervals may be more advantageous than at half-yearly intervals. Although 27.3 and 42.9% of the pre-MDA low- and medium-intensity mf carriers, respectively, showed CFA (Table 3), indicating adult worm presence, all of them except one were found to be amicrofilaraemic and are currently less important from a transmission perspective. Their becoming microfilaraemic in future and causing transmission depends upon the reproductive potential of the adult worms in them. The annual transmission potential (ATP) in the study community was 2690 before mass DEC administration, 852 and 1576 during the initial two rounds of MDA, and 50 to 237 during the third to sixth round of MDA (Ramaiah et al., 2003b), and the number of infective mosquitoes showed a further declining trend during the seventh to tenth MDA (K.D. Ramaiah, unpublished data). Hence, most of the surviving adult worms in this category of individuals might have resulted from infection acquired before the third MDA, when the ATP was substantial. These worms are more than 8—9 years old, near to the upper limit of the life span (Leeuwin, 1962; Subramanian et al., 2004; Vanamail et al., 1990). ATP during some years after the third MDA was also more than 100, the estimated safe level (Ramaiah et al., 1994). Hence, a smaller proportion of adult worms might have resulted from infection acquired after the third MDA. These worms, although less than 8—9 years old, were exposed to treatment over an eight-year period. Simonsen et al. (2005) reported a 94% reduction, after seven to eight DEC treatments, in
254 intensity of CFA in pre-MDA mf carriers, suggesting that the adult worm load in these individuals is very meagre and may gradually diminish. Persistence of microfilaraemia in two of the four pre-MDA high-intensity mf carriers, even after 6.3 ± 1.0 treatments (Table 3), indicates that the risk of microfilaraemic individuals remaining microfilaraemic (Meyrowitsch et al., 2004) is higher in high-intensity mf carriers. This, however, requires further confirmation, as we were able to include only four high-intensity mf carriers in this study. Also, the households of both the persistent mf carriers contained at least one more mf carrier before MDA, suggesting more intense transmission within these households. This, combined with slow clearance of infection in this category of individuals (Table 3), necessitates more treatments to cure infection in high-intensity mf carriers and their household members. They constituted 1.8% of the population and 14.6% of the total mf carriers and were distributed in 8.2% of the households in the village before MDA. No feasible techniques are available to detect these households to give intensive treatment to their members. Therefore, it may be necessary to continue mass DEC treatment beyond 10 rounds, until the mf rate is reduced to <1% (WHO, 2005b) and mf intensity is at a safe level in these communities. Absence of CFA in preMDA amicrofilaraemic individuals (Table 2), persistence of CFA as well as microfilaraemia in high-intensity mf carriers and decreased clearance of CFA with increase in mf intensity suggest that clearance of CFA (Table 3), an indication of macrofilaricidal effect of annual DEC treatment, is more related to pre-treatment adult worm burden. By contrast to the highly endemic large villages, control/elimination of LF may be less difficult and possible with four to eight rounds of mass DEC administration in low endemic and small villages in Culex vector areas (Ramaiah et al., 2002, 2003b), as the proportion and number of highdensity mf carriers is likely to be smaller. This necessitates differentiation of highly endemic villages from low endemic ones, using a criterion such as the number of chronic patients, as the number of MDAs required for both the category of villages is different. Although excluded from treatment, none of the children in the 2—5 years age group (mean body weight <15 kg) was CFA-positive in this study, compared with a 22.2% positive rate after six rounds of MDA (Ramaiah et al., 2003a). The youngest CFA-positive child was 8 years old, suggesting that no new infections occurred during the last 7 years of MDA. Only one child, 10 years of age, was positive for both CFA and mf, and her household had two more mf carriers before MDA — one with a high count of 930 mf. This finding re-emphasizes the risk posed by the households with high intensity and multiple mf carriers to cause transmission and new infections. Occurrence of CFA in 8—10-year-old children (Table 2) is not surprising, because they were born before the third MDA, when substantial transmission occurred, and were included for treatment only after they became 5 years of age (mean body weight 15 kg) and received only a few or no treatments (Table 2). This study showed that DEC exerts a better macrofilaricidal effect in low-intensity mf carriers. The prevalence and intensity of infection in children are generally low (Stolk et al., 2004) and hence are expected to be more amenable to DEC treatment. The inclusion of children in MDA from the age of 2 years, as envisaged by the GPELF, and from
K.D. Ramaiah et al. the very initial rounds of MDA is important to prevent new infections and protect the children from subsequent clinical consequences (Witt and Ottesen, 2001). Existence of risk of transmission during the initial rounds of MDA also highlights the fact that monitoring and evaluation of children born during this period will yield more robust information on the impact of MDA. The treatment coverage of 55 to 75%, observed in the present study village, is similar to that observed in many LF elimination programmes (Babu and Kar, 2004; de Rochars et al., 2005; Ramaiah et al., 2000) but is less than the effective treatment coverage of 80%. Effective treatment coverage may yield better results than those reported in this study. We conclude that six to seven DEC treatments per individual have the potential to totally suppress micfofilaraemia in all individuals, except in some of those with heavy infection. Slightly less than half of the pre-MDA mf carriers continue to be positive for CFA, but a vast majority of them turned amicrofilaraemic. More follow-up studies in highly endemic villages may be necessary to understand the course of infection in individuals with high intensities of infection and the prospects of elimination of LF. Conflicts of interest statement The authors have no conflicts of interest concerning the work reported in this paper.
Acknowledgements We express our gratitude to the villagers of Alagramam for their co-operation and participation in the study. We are thankful to Mr Bashir Ahmed and Mr S.B. Chakravarthy, Vector Control Research Centre (VCRC), Pondicherry, for their help in collecting and processing the blood films and carrying out ICT card tests. Our thanks are due to Dr S. Subramanian, VCRC, for his critical remarks on the manuscript. We thank Drs Hans Remme, Gautam Biswas, Boatin and Kumaraswamy for their constant support to the study team. Part of the study received financial support from UNDP/World Bank/WHO/TDR under the grant no. 920702.
References Babu, B.V., Kar, S.K., 2004. Coverage, compliance and some operational issues of mass drug administration during the programme to eliminate lymphatic filariasis in Orissa, India. Trop. Med. Int. Health 9, 702—709. Bockarie, M.J., Tisch, D.J., Kastens, W., Alexander, N.D., Dimber, Z., Bockarie, F., Ibam, E., Alpers, M.P., Kazura, J.W., 2002. Mass treatment to eliminate filariasis in Papua New Guinea. N. Eng. J. Med. 23, 1841—1848. Chanteau, S., Moulia-Pelat, J.P., Glaziou, P., Nguyen, N.L., Luquiaud, P., Plichart, C., Martin, P.M.V., Cartel, J.L., 1994. Og4C3 circulating antigen: a marker of infection and adult worm burden in Wuchereria bancrofti filariasis. J. Infect. Dis. 120, 247—250. Das, P.K., Ramaiah, K.D., Vanamail, P., Pani, S.P., Yuvaraj, J., Balarajan, K., Bundy, D.A.P., 2001. Placebo-controlled community trial of four cycles of single-dose diethylcarbamazine or ivermectin against Wuchereria bancrofti infection and transmission in India. Trans. R. Soc. Trop. Med. Hyg. 95, 336—341. de Rochars, M.B., Kanjilal, S., Direny, A.N., Radday, J., Lafontant, J.G., Mathieu, E., Rheingans, R.D., Haddix, A.C., Streit, T.G.,
Yearly MDA of DEC and Wuchereria bancrofti infection Beach, M.J., Addiss, D.G., Lammie, P.J., 2005. The Leogane, Haiti demonstration project: decreased microfilaremia and program costs after three years of mass drug administration. Am. J. Trop. Med. Hyg. 73, 888—894. Eberhard, M.L., Hightower, A.W., Addiss, D.G., Lammie, P.J., 1997. Clearance of Wuchereria bancrofti antigen after treatment with diethylcarbamazine or ivermectin. Am. J. Trop. Med. Hyg. 57, 483—486. Farid, H.A., Hammad, R.E., Soliman, D.A., El Setouhy, M., Ramzy, R.M.R., Weil, G.J., 2003. Relationships between Wuchereria bancrofti microfilaraemia in human blood and parasite uptake and maturation in Culex pipiens, with observations on the effect of diethylcarbamazine treatment on these parameters. Am. J. Trop. Med. Hyg. 68, 286—293. Fraser, M., Taleo, G., Taleo, F., Yaviong, J., Amos, M., Babu, M., Kalkoa, M., 2005. Evaluation of the program to eliminate lymphatic filariasis in Vanuatu following two years of mass drug administration implementation: results and methodologic approach. Am. J. Trop. Med. Hyg. 73, 753—758. Freedman, D.O., Plier, D.A., de Almeida, A.B., de Oliveira, A.L., Miranda, J., Braga, C., 2001. Effect of aggressive prolonged diethylcarbamazine therapy on circulating antigen levels in bancroftian filariasis. Trop. Med. Int. Health 6, 37—41. Hairston, N.G., Jachowski, L.A., 1968. Analysis of the Wuchereria bancrofti population in the people of American Samoa. Bull. World Health Organ. 38, 29—59. Ismail, M.M., Weil, G.J., Jayasinghe, K.S.A., Premaratne, U.N., Abeyewickreme, W., Rajaratnam, H.N., Sheriff, H.R., Perera, C.S., Dissanaike, A.S., 1996. Prolonged clearance of microfilaraemia in patients with bancroftian filariasis after multiple high doses of ivermectin or diethylcarbamazine. Trans. R. Soc. Trop. Med. Hyg. 90, 684—688. Kazura, J., Greenberg, J., Perry, R., Weil, G.J., Day, K., Alpers, M., 1993. Comparison of single-dose diethylcarbamazine and ivermectin for treatment of bancroftian filariasis in Papua New Guinea. Am. J. Trop. Med. Hyg. 49, 804—811. Leeuwin, R.S., 1962. Microfilaraemia in Surinamese living in Amsterdam. Trop. Geogr. Med. 14, 355—360. McCarthy, J.S., Guinea, A., Weil, G.J., Ottesen, E.A., 1995. Clearance of circulating filarial antigen as a measure of the macrofilaricidal activity of diethylcarbamazine in Wuchereria bancrofti infection. J. Infect. Dis. 172, 521—526. Meyrowitsch, D.W., Simonsen, P.E., Magesa, S.M., 2004. Long-term effect of three different strategies for mass diethylcarbamazine administration in bancroftian filariasis: follow-up at 10 years after treatment. Trans. R. Soc. Trop. Med. Hyg. 98, 627—634. Nicolas, L., Plichart, C., Nguyen, L.N., Moulia-Pelat, J.P., 1997. Reduction of Wuchereria bancrofti adult worm circulating antigen after annual treatments of diethylcarbamazine combined with ivermectin in French Polynesia. J. Infect. Dis. 175, 489—492. Pani, S.P., Hoti, S.L., Elango, A., Yuvaraj, Y., Lal, R., Ramaiah, K.D., 2000. Evaluation of ICT whole blood antigen card test to detect infection due to nocturnally periodic Wuchereria bancrofti in south India. Trop. Med. Int. Health 5, 359—363. Pani, S.P., Subramaniam Reddy, G., Das, L.K., Vanamail, P., Hoti, S.L., Ramesh, J., Das, P.K., 2002. Tolerability and efficacy of single dose albendazole, Diethylcarbamazine citrate (DEC) or co-administration of albendazole with DEC in the clearance of Wuchereria bancrofti in asymptomatic microfilaraemic volunteers in Pondicherry, south India: a hospital based study. Filaria J. 1, 1—11. Rajendran, R., Sunish, I.P., Mani, T.R., Munirathinam, A., Abdullah, S.M., Arunachalam, N., Satyanarayana, K., 2004. Impact of two annual single-dose mass drug administrations with diethylcarbamazine alone or in combination with albendazole on Wuchereria bancrofti microfilaraemia and antigenaemia in south India. Trans. R. Soc. Trop. Med. Hyg. 98, 174—181.
255 Ramaiah, K.D., Das, P.K., Dhanda, V., 1994. Estimation of permissible levels of transmission of bancroftian filariasis based on some entomological and parasitological results of a 5-year vector control programme. Acta Trop. 56, 89—96. Ramaiah, K.D., Das, P.K., Appavoo, N.C., Ramu, K., Augustin, D.J., Vijay Kumar, K.N., Chandrakala, A.V., 2000. A programme to eliminate lymphatic filariasis in Tamil Nadu state, India: compliance with annual single dose DEC mass treatment and some related operational aspects. Trop. Med. Int. Health 5, 842—847. Ramaiah, K.D., Vanamail, P., Pani, S.P., Yuvaraj, J., Das, P.K., 2002. The effect of six rounds of single dose mass treatment with diethylcarbamazine or ivermectin on Wuchereria bancrofti infection and its implications for lymphatic filariasis elimination. Trop. Med. Int. Health 7, 767—774. Ramaiah, K.D., Vanamail, P., Pani, S.P., Yuvaraj, J., Das, P.K., 2003a. The prevalence of Wuchereria bancrofti antigenaemia in communities given six rounds treatment with diethylcarbamazine, ivermectin or placebo tablets. Ann. Trop. Med. Parasitol. 97, 737—741. Ramaiah, K.D., Vanamail, P., Pani, S.P., Yuvaraj, J., Das, P.K., 2003b. The impact of six rounds of single dose mass administration of diethylcarbamazine or ivermectin on the transmission of Wuchereria bancrofti by Culex quinquefasciatus. Trop. Med. Int. Health 8, 1—11. Ramzy, R.M., El Setouhy, M., Helmy, H., Kandil, A.M., Ahmed, E.S., Farid, H.A., Faris, R., Weil, G.J., 2002. The impact of singledose diethylcarbamazine treatment of bancroftian filariasis in a low-endemicity setting in Egypt. Am. J. Trop. Med. Hyg. 67, 196—200. Schuetz, A., Addiss, D.G., Eberhard, M.L., Lammie, P.J., 2000. Evaluation of the whole blood filariasis ICT test for short-term monitoring after antifilarial treatment. Am. J. Trop. Med. Hyg. 62, 502—503. Simonsen, P.E., Magesa, S.M., Meyrowitsch, D.W., Malecela-Lazaro, M.N., Rwegoshora, R.T., Jaoko, W.G., Michael, E., 2005. The effect of eight half-yearly single-dose treatments with DEC on Wuchereria bancrofti circulating antigenaemia. Trans. R. Soc. Trop. Med. Hyg. 99, 541—547. Stolk, W.A., Ramaiah, K.D., Van Oortmarssen, G.J., Das, P.K., Habbema, J.D.F., De Vlas, S.J., 2004. Meta-analysis of ageprevalence patterns in lymphatic filariasis: no decline in microfilaraemia prevalence in older age groups as predicted by models with acquired immunity. Parasitology 129, 605—612. Subramanian, S., Habbema, J.D.F., Ramaiah, K.D., Stolk, W.A., Krishnamoorthy, K., van Oortmarssen, G.J., Amalraj, D., Plaisier, A.P., Das, P.K., 2004. The dynamics of Wuchereria bancrofti infection: a model-based analysis of longitudinal data from Pondicherry, India. Parasitology 128, 467—482. Vanamail, P., Subramanian, S., Das, P.K., Pani, S.P., Rajagopalan, P.K., 1990. Estimation of fecundic life span of Wuchereria bancrofti from longitudinal study of human infection in an endemic area of Pondicherry (south India). Ind. J. Med. Res. 91, 293—297. Weil, G.J., Sethumadhavan, K.V., Santhanam, S., Jain, D.C., Ghosh, T.K., 1988. Persistence of parasite antigenaemia following diethylcarbamazine therapy of bancroftian filariasis. Am. J. Trop. Med. Hyg. 38, 589—595. Weil, G.J., Ramzy, R.M., Chandrashekar, R., Gad, A.M., Lowrie Jr., R.C., Faris, R., 1996. Parasite antigenemia without microfilaremia in bancroftian filariasis. Am. J. Trop. Med. Hyg. 55, 333—337. Witt, C., Ottesen, E.A., 2001. Lymphatic filariasis: an infection of childhood. Trop. Med. Int. Health 6, 582—606. WHO, 2005a. Global programme to eliminate lymphatic filariasis. Wkly Epidemiol. Rec. 80, 202—212. WHO, 2005b. Monitoring and epidemiological assessment of the programme to eliminate lymphatic filariasis at implementation unit level. World Health Organization, Geneva, WHO/CDS/CPE/CEE 2005.50.