- Email: [email protected]
Seroprevalence of Taenia solium antibodies in Vellore district, south India
Transactions of the Royal Society of Tropical Medicine and Hygiene (2008) 102, 246—250
available at www.sciencedirect.com
journal homepage: www.elsevierhealth.com/journals/trst
Seroprevalence of Taenia solium antibodies in Vellore district, south India V. Prabhakaran a, M. Venkata Raghava b, V. Rajshekhar a, J. Muliyil b, A. Oommen a,∗ a b
Department of Neurological Sciences, Christian Medical College, Vellore 632 004, India Department of Community Health, Christian Medical College, Vellore, India
Received 24 July 2007; received in revised form 19 October 2007; accepted 19 October 2007 Available online 3 December 2007
KEYWORDS Neurocysticercosis; Cysticercus; Antibodies; Seroprevalence; India
Summary Although Taenia solium neurocysticercosis is the cause of almost one-third of epilepsy in Vellore district, south India, the level of exposure to T. solium in the district is not known. This study determined the seroprevalence of cysticercus antibodies in seizure-free, study subjects aged 2—60 years from urban and rural areas of Vellore district. Cysticercus antibodies, as determined by immunoblots, were noted in 15.9% of 1063 people and were significantly higher in the rural population (17.7%) compared with the urban population (6.0%). Twenty-four percent of the rural population and 12% of the urban population ate pork. Onethird of all households in the district had one or more members seropositive for cysticercus antibodies. The high index of exposure to T. solium in south India calls for improved animal husbandry and sanitation. © 2007 Royal Society of Tropical Medicine and Hygiene. Published by Elsevier Ltd. All rights reserved.
1. Introduction Taenia solium, the pork tapeworm, causes two diseases in humans: taeniasis and cysticercosis. Taeniasis is an intestinal disease acquired by ingestion of viable T. solium larvae from pork, while cysticercosis is acquired by the ingestion of T. solium eggs. The serious T. solium infections are those of the central nervous system (CNS) and of the eye. Neurocysticercosis (NCC) is the most common parasitic infection of
∗
Corresponding author. Tel.: +91 416 2282701; fax: +91 416 2232035. E-mail address: [email protected] (A. Oommen).
the CNS and a common cause of recently acquired seizures in Latin America, sub-Saharan Africa and Asia, where it is endemic (Garc´ıa et al., 2003b). In India, NCC accounts for almost one-third of all epilepsy cases (Rajshekhar et al., 2006). Poor sanitation and animal husbandry practices are risk factors for NCC (Rodriguez-Canul et al., 1999). There may also be country-specific conditions that contribute to the transmission of NCC. In India these may include societal factors. For example, pig rearing is a caste-based occupation, and pig rearers live in specified areas of a village or town. A few pig-rearing communities are migratory in nature. These social constraints may influence the demographics of cysticercosis in the community, forming nodes
0035-9203/$ — see front matter © 2007 Royal Society of Tropical Medicine and Hygiene. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.trstmh.2007.10.010
Seroprevalence of Taenia solium antibodies in Vellore district, south India for disease transmission. Prasad et al. (2002) found that in Uttar Pradesh the prevalence of intestinal taeniasis among 72 members of a pig-farming community was as high 38% and that of porcine cysticercosis was also high, at 26%, in 50 of their pigs slaughtered for consumption. In a larger study covering 30 villages, Prasad et al. (2007) noted the prevalence of taeniasis to be 18.6% in pig-farming communities in north India. Interventions in the community aimed at substantially reducing the rates of NCC infection can take several forms. It is essential to know the extent to which the population is exposed to the infecting organism when determining goals to control disease and prevent transmission. The exposure to NCC is not known in south India but can be determined from the seroprevalence of cysticercus antibodies in the community. To establish the level of exposure of the population in south India to T. solium, a serological study measuring cysticercus antibodies to infection-specific antigens was carried out in a district of the south Indian state of Tamil Nadu.
247
around 2500 randomly chosen from Kaniyambadi Block, with a population over 100 000 (82 village panchayats) experiencing similar social and cultural characteristics. In the urban areas, similar geographically demarcated areas are called wards (which come under the district municipality), and four wards were randomly selected out of >45 wards. In each of the 20 clusters, 20 families, assumed to be of four members each, were selected using a systematic sampling technique and a random start. The selected population of 1600 was 75% rural and 25% urban, to represent the distribution in the country. Information on pork consumption and living in a pig-rearing or non-pig-rearing region of a village or ward was obtained from all the population sampled. Between March 2004 and February 2005 blood (2—5 ml) was drawn from all consenting individuals and transported cold to the laboratory at the Christian Medical College, Vellore, within 4 h of collection. Serum was stored at −20 ◦ C until assay.
2.4. Cysticercus serology
2. Materials and methods 2.1. Study region The seroprevalence of cysticercus antibodies was determined in a rural and urban population of Vellore district, which is one of 30 districts in the state of Tamil Nadu, south India. The male:female ratio is nearly equal in Vellore district. The population of Tamil Nadu is 62 million and that of Vellore district 3.5 million. The rural population was from Kaniyambadi Block, an area of 182 km2 , 85 villages and 105 000 people. The urban population was 300 000 people from Vellore town. Kaniyambadi Block is a rural development block south of Vellore and has served as the field practice area of the Community Health Department for nearly 50 years. The Department provides comprehensive health and development services to the entire block, enabling good rapport with the community. Kaniyambadi Block and Vellore town border each other; they are connected by road and their populations intermingle. Agriculture and animal husbandry are the major occupations of the rural population, while pig rearing and pork consumption occur in both populations. The average literacy rate of Vellore town is 74% (male 80% and female 68%). The population under study is representative of the state of Tamil Nadu.
2.2. Study population The study population covered 50 617 people who had been screened for active epilepsy, of whom 38 105 were rural and 12 512 were urban (Rajshekhar et al., 2006).
2.3. Study design The seroprevalence of cysticercus antibodies was studied in people aged 2—60 years from 20 clusters. Rural clusters in the study are village panchayats (settlements of people with local self-governance), each with a population of
Cysticercus antibodies were determined in sera on immunoblots against lentil lectin-specific T. solium glycoproteins, as described by Prabhakaran et al. (2004). Sera were considered positive for cysticercus antibodies by the criteria of Tsang et al. (1989), i.e. reaction to one or more T. solium glycoproteins of molecular weights 50, 38—42, 24, 21, 18, 14 and 13 kDa. Blots were read independently by two laboratory personnel. The immunoblot detects antibodies to T. solium glycoproteins that are specific and diagnostic for cysticercosis. In this study, in a community that had been screened for active epilepsy/recent onset seizures and were asymptomatic, a positive immunoblot suggests silent NCC, systemic cysticercosis or a past infection and was taken as an index of exposure to T. solium.
2.5. Statistical analysis Data were analyzed for significant differences by the 2 test and were considered significant at P < 0.05.
3. Results Serology was determined in 1063 people who consented to provide blood, sampled from a population of 50 423 who were seizure-free (Rajshekhar et al., 2006): 84.4% of the samples were from the rural population and 15.6% from the urban population. The population seroprevalence of cysticercus antibodies was significantly higher in the rural population compared with the urban population among both men and women (Figure 1). People living in rural areas were three times more likely to be seropositive for cysticercus antibodies than their urban counterparts (P < 0.001). The prevalence of cysticercus antibodies was significantly higher in rural women than in rural men but did not differ between urban men and women (Figure 1). Stratified for age, seroprevalence was highest in young adults (16—45 years) and in young adult rural women (Figure 2).
248
V. Prabhakaran et al.
Figure 1
Seroprevalence of cysticercus antibodies to Taenia solium in Vellore district, south India.
in this study ate pork that had not been subjected to meat inspection.
4. Discussion A seroprevalence of nearly 16% for cysticercus antibodies in Vellore district, where one-third of all households have one or more members seropositive for the antibodies, is high and categorizes the district as hyperendemic for exposure to T. solium. The immunoblot used in this study under-reports infections with a single cyst (60% sensitive) (Prabhakaran et al., 2004), suggesting that the prevalence in Vellore district may be higher than stated. This is important, as almost one-third of all epilepsy in Vellore district is due to NCC (Rajshekhar et al., 2006). The high seroprevalence among adults of the district may reflect the known increased susceptibility to infection with age (Fleury et al., 2004). Although the population included in this study was seizurefree, seropositive individuals need follow-up to ensure that anyone with symptoms, particularly for NCC, seeks medical advice. A main finding of the study was the significantly higher seroprevalence in the rural population compared with the urban population. Reasons for this could be varied, with different sociocultural background and practices, of which the higher prevalence of consuming pork may also contribute. The higher seroprevalence in the rural population may also reflect poorer sanitation and therefore greater environmental fecal contamination in rural communities, although the proportion of rural and urban populations living in pigrearing areas were comparable in this study (60—63%). This
Figure 2 Age and seroprevalence of cysticercus antibodies in Vellore district, south India. : rural population; : urban population.
Blood samples from the rural population were obtained from 296 households in 16 clusters of 22 villages. Seroprevalence in these villages ranged from 3.2 to 42.6%. In 36.1% of the households, one or more members were positive for cysticercus antibodies (Table 1). Blood samples from the urban population were obtained from 52 households in four wards, where seroprevalence for cysticercus antibodies ranged from 0 to 15.9%. In 17.3% of these households, one or more members were positive for cysticercus antibodies (Table 1). The proportions of the urban and rural populations in this study living in pig-rearing areas of the town or village were 59.6 and 63.2%, respectively. Twelve percent of the urban population and 24.2% of the rural population sampled
Table 1
Distribution of cysticercus antibodies in Vellore district, south India
Population
No. sera
Cysticercus antibody seroprevalence (%)
No. households tested
% households with positive immunoblots ≥2 people
1 person
0 people
Rural Urban
897 166
17.7 6.0
296 52
13.2 1.9
22.9 15.4
63.9 82.7
Total
1063
15.9
348
11.5
21.8
66.7
Seroprevalence of Taenia solium antibodies in Vellore district, south India has been shown in other endemic areas (Fleury et al., 2006). Seropositivity in over one-third of all rural households, with 13% of the households having two or more members positive for cysticercus antibodies, would corroborate high environmental contamination with T. solium. Studies from Peru have noted increased seropositivity among contacts of tapeworm carriers (Garc´ıa et al., 2003a). Although seroprevalence is lower in the urban population of Vellore district, seropositivity in 17.3% of households in a population of 300 000 does indicate significant exposure to T. solium. The rural and urban areas of Vellore district studied are representative of living and environmental conditions in most of India, and it is probable that seroprevalence of T. solium antibodies is equally high in other parts of the country. This is borne out in studies by Khurana et al. (2006), who analyzed 600 sera by ELISA and found a seroprevalence of 17.3% for cysticercus antibodies in Chandigarh, north India. They also noted higher prevalence in rural (20%) compared with urban (8%) populations and, importantly, that the highest prevalence was among people who lived in close contact with pigs and who had poor sanitation and water facilities. Thus their study also suggests that in Indian communities there are pockets in the population from which T. solium infections may spread. As in the present study, they also noted high cysticercus antibody seroprevalence in women and attributed it to eating unwashed, raw vegetables while cooking. A seroprevalence of 15—17% in the general population in India is comparable to, and in several instances much higher than, that in countries endemic for T. solium cysticercosis and where it is determined by levels of T. solium in the environment. In other countries of Asia, seroprevalence ranges from 1.65% in Indonesia to 3.97—16.4% in China (Chung et al., 2005; Li et al., 2006; Sutisna et al., 1999). Studies from Viet Nam found circulating cyst antigen to range from 5.3% in mountainous rural regions to 0% in urban populations (Somers et al., 2006). In West Africa, Togo and Benin report seroprevalence at a conservative 2.4 and 1.3%, respectively (Zoli et al., 2003), while the levels in Burundi, Eastern/Central Africa are 30% (Nsengiyumva et al., 2003). In South America, population seroprevalence of cysticercus antibodies has been studied extensively, and ranges from 13.7% in the highlands to 24.2% on the coast in Peru (Montano et al., 2005). Seroprevalence in central—western Brazil is 11.3% and higher for those living in areas of poor sanitation (Oliveira et al., 2006); it is 5.6 and 2.1% in urban and rural Brazil, respectively (Bragazza et al., 2002; Silveira-Lacerda Ede et al., 2002). In rural Mexico, seroprevalence is reported at 3.7% (Rodriguez-Canul et al., 1999). These seroprevalence studies provide evidence that populations in large parts of the world are exposed to T. solium. Although exposure to T. solium per se does not translate into infection, as up to 40% of people seropositive for T. solium do not develop the infection (Fleury et al., 2006; Meza-Lucas et al., 2003), a population seroprevalence of 16% for cysticercus antibodies emphasizes the pervasiveness of T. solium in Vellore district. Future studies need to determine risk of occupation (pig rearing) and importance of humanto-human egg transmission on cysticercus seropositivity, as the high index of exposure to T. solium, with its origins in poor animal husbandry and sanitation, is clearly of public health concern in India.
249
Authors’ contributions: VR, JM and AO designed the study and drafted the manuscript; VP carried out all laboratory work; MVR carried out the community studies. All authors analyzed the data and read and approved the final manuscript. AO, VR and JM are guarantors for the paper. Acknowledgements: The authors thank G. George Martin, J. Vijayakumar, N. Arulraj, N. Ethiraj and P. Babu for their expert assistance in collecting and processing blood samples. Funding: The study was supported in part by a Task Force grant from the Indian Council of Medical Research, New Delhi, India (D.O.No. SWG/Neuro/3/2001-NCD-1). Conflicts of interest: None declared. Ethical approval: Institutional Review Board of the Christian Medical College, Vellore, India (R.C. Min No 4638).
References Bragazza, L.M., Vaz, A.J., Passos, A.D., Takayanagui, O.M., Nakamura, P.M., Espindola, N.M., Pardini, A., Bueno, E.C., 2002. Frequency of serum anti-cysticercus antibodies in the population of a rural Brazilian community (Cassia dos coqueiros, SP) determined by Elisa and immunoblotting using Taenia crassiceps antigens. Rev. Inst. Med. Trop. Sao Paulo 44, 7—12. Chung, J.Y., Eom, K.S., Yang, Y., Li, X., Feng, Z., Rim, H.J., Cho, S.Y., Kong, Y., 2005. A seroepidemiological survey of Taenia solium cysticercosis in Nabo, Guangxi Zhuang Autonomous Region, China. Korean J. Parasitol. 43, 135—139. Fleury, A., Dessein, A., Preux, P.M., Dumas, M., Tapia, G., Larralde, C., Sciutto, E., 2004. Symptomatic human neurocysticercosis—– age, sex and exposure factors relating with disease heterogeneity. J. Neurol. 251, 830—837. Fleury, A., Morales, J., Bobes, R.J., Dumas, M., Y˜ anez, O., Pi˜ na, J., Carrillo-Mezo, R., Martinez, J.J., Fragoso, G., Dessein, A., Larralde, C., Sciutto, E., 2006. An epidemiological study of familial neurocysticercosis in an endemic Mexican community. Trans. R. Soc. Trop. Med. Hyg. 100, 551—558. Garc´ıa, H.H., Gilman, R.H., Gonzalez, A.E., Verastegui, M., Rodriguez, S., Gavidia, C., Tsang, V.C., Falcon, N., Lescano, A.G., Moulton, L.H., Bernal, T., Tovar, M., Cysticercosis Working Group in Peru, 2003a. Hyperendemic human and porcine Taenia solium infection in Peru. Am. J. Trop. Med. Hyg. 68, 268—275. Garc´ıa, H.H., Gonzalez, A.E., Carlton, A.W., Evans, C.A.W., Gilman, R.H., 2003b. Taenia solium cysticercosis. Lancet 362, 547—556. Khurana, S., Aggarwal, A., Malla, N., 2006. Prevalence of anticysticercus antibodies in slum, rural and urban populations in and around Union territory, Chandigarh. Indian J. Pathol. Microbiol. 49, 51—53. Li, T., Craig, P.S., Ito, A., Chen, X., Qiu, D., Qiu, J., Sato, M.O., Wandra, T., Bradshaw, H., Li, L., Yang, Y., Wang, Q., 2006. Taeniasis/cysticercosis in a Tibetan population in Sichuan Province, China. Acta Trop. 100, 223—231. Meza-Lucas, A., Carmona-Miranda, L., Garc´ıa-Jeranimo, R.C., Torrero-Miranda, A., Gonzalez-Hidalgo, G., Lapez-Castellanos, G., Correa, D., 2003. Short report: limited and short-lasting humoral response in Taenia solium: seropositive households compared with patients with neurocysticercosis. Am. J. Trop. Med. Hyg. 69, 223—227. Montano, S.M., Villaran, M.V., Ylquimiche, L., Figueroa, J.J., Rodriguez, S., Bautista, C.T., Gonzalez, A.E., Tsang, V.C., Gilman, R.H., Garcia, H.H., Cysticercosis Working Group in Peru,
250 2005. Neurocysticercosis: association between seizures, serology, and brain CT in rural Peru. Neurology 65, 229—233. Nsengiyumva, G., Druet-Cabanac, M., Ramanankandrasana, B., Bouteille, B., Nsizabira, L., Preux, P.M., 2003. Cysticercosis as a major risk factor for epilepsy in Burundi, East Africa. Epilepsia 44, 950—955. Oliveira, H.B., Rodrigues, R.M., Barcelos, I.S., Silva, L.P., CostaCruz, J.M., 2006. Anti-Taenia solium metacestode IgG antibodies in serum samples from inhabitants of a central-western region of Brazil. Rev. Inst. Med. Trop. Sao Paulo 48, 49—52. Prabhakaran, V., Rajshekhar, V., Murrell, K.D., Oommen, A., 2004. Taenia solium metacestode glycoproteins as diagnostic antigens for solitary cysticercus granuloma in Indian patients. Trans. R. Soc. Trop. Med. Hyg. 98, 478—484. Prasad, K.N., Chawla, S., Jain, D., Pandey, C.M., Pal, L., Pradhan, S., Gupta, R.K., 2002. Human and porcine Taenia solium infection in rural north India. Trans. R. Soc. Trop. Med. Hyg. 96, 515—516. Prasad, K.N., Prasad, A., Gupta, R.K., Pandey, C.M., Singh, U., 2007. Prevalence and associated risk factors of Taenia solium taeniasis in a rural pig farming community of north India. Trans. R. Soc. Trop. Med. Hyg., 101. Rajshekhar, V., Raghava, M.V., Prabhakaran, V., Oommen, A., Muliyil, J., 2006. Active epilepsy as an index of burden of neurocysticercosis in Vellore district, India. Neurology 67, 2135—2139.
V. Prabhakaran et al. Rodriguez-Canul, R., Fraser, A., Allan, J.C., Dominguez-Alpizar, J.L., Argaez-Rodriguez, F., Craig, P.S., 1999. Epidemiological study of Taenia solium taeniasis/cysticercosis in a rural village in Yucatan state, Mexico. Ann. Trop. Med. Parasitol. 93, 57—67. Silveira-Lacerda Ede, P., Machado, E.R., Arantes, S.C., Costa-Cruz, J.M., 2002. Anti-Taenia solium metacestodes antibodies in serum from blood donors from four cities of Tri˜ angulo Mineiro area, Minas Gerais, Brazil, 1995. Rev. Inst. Med. Trop. Sao Paulo 44, 229—231. Somers, R., Dorny, P., Nguyen, V.K., Dang, T.C., Goddeeris, B., Craig, P.S., Vercruysse, J., 2006. Taenia solium taeniasis and cysticercosis in three communities in north Vietnam. Trop. Med. Int. Health 11, 65—72. Sutisna, I.P., Fraser, A., Kapti, I.N., Rodriguez-Canul, R., Puta Widjana, D., Craig, P.S., Allan, J.C., 1999. Community prevalence study of taeniasis and cysticerosis in Bail, Indonesia. Trop. Med. Int. Health 4, 288—294. Tsang, V.C., Brand, J.A., Boyer, A.E., 1989. An enzyme-linked immunoelectrotransfer blot assay and glycoprotein antigens for diagnosing human cysticercosis Taenia solium. J. Infect. Dis. 159, 50—59. Zoli, A., Shey-Njila, O., Assana, E., Nguekam, J.P., Dorny, P., Brandt, J., Geerts, S., 2003. Regional status, epidemiology and impact of Taenia solium cysticercosis in Western and Central Africa. Acta Trop. 87, 35—42.
available at www.sciencedirect.com
journal homepage: www.elsevierhealth.com/journals/trst
Seroprevalence of Taenia solium antibodies in Vellore district, south India V. Prabhakaran a, M. Venkata Raghava b, V. Rajshekhar a, J. Muliyil b, A. Oommen a,∗ a b
Department of Neurological Sciences, Christian Medical College, Vellore 632 004, India Department of Community Health, Christian Medical College, Vellore, India
Received 24 July 2007; received in revised form 19 October 2007; accepted 19 October 2007 Available online 3 December 2007
KEYWORDS Neurocysticercosis; Cysticercus; Antibodies; Seroprevalence; India
Summary Although Taenia solium neurocysticercosis is the cause of almost one-third of epilepsy in Vellore district, south India, the level of exposure to T. solium in the district is not known. This study determined the seroprevalence of cysticercus antibodies in seizure-free, study subjects aged 2—60 years from urban and rural areas of Vellore district. Cysticercus antibodies, as determined by immunoblots, were noted in 15.9% of 1063 people and were significantly higher in the rural population (17.7%) compared with the urban population (6.0%). Twenty-four percent of the rural population and 12% of the urban population ate pork. Onethird of all households in the district had one or more members seropositive for cysticercus antibodies. The high index of exposure to T. solium in south India calls for improved animal husbandry and sanitation. © 2007 Royal Society of Tropical Medicine and Hygiene. Published by Elsevier Ltd. All rights reserved.
1. Introduction Taenia solium, the pork tapeworm, causes two diseases in humans: taeniasis and cysticercosis. Taeniasis is an intestinal disease acquired by ingestion of viable T. solium larvae from pork, while cysticercosis is acquired by the ingestion of T. solium eggs. The serious T. solium infections are those of the central nervous system (CNS) and of the eye. Neurocysticercosis (NCC) is the most common parasitic infection of
∗
Corresponding author. Tel.: +91 416 2282701; fax: +91 416 2232035. E-mail address: [email protected] (A. Oommen).
the CNS and a common cause of recently acquired seizures in Latin America, sub-Saharan Africa and Asia, where it is endemic (Garc´ıa et al., 2003b). In India, NCC accounts for almost one-third of all epilepsy cases (Rajshekhar et al., 2006). Poor sanitation and animal husbandry practices are risk factors for NCC (Rodriguez-Canul et al., 1999). There may also be country-specific conditions that contribute to the transmission of NCC. In India these may include societal factors. For example, pig rearing is a caste-based occupation, and pig rearers live in specified areas of a village or town. A few pig-rearing communities are migratory in nature. These social constraints may influence the demographics of cysticercosis in the community, forming nodes
0035-9203/$ — see front matter © 2007 Royal Society of Tropical Medicine and Hygiene. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.trstmh.2007.10.010
Seroprevalence of Taenia solium antibodies in Vellore district, south India for disease transmission. Prasad et al. (2002) found that in Uttar Pradesh the prevalence of intestinal taeniasis among 72 members of a pig-farming community was as high 38% and that of porcine cysticercosis was also high, at 26%, in 50 of their pigs slaughtered for consumption. In a larger study covering 30 villages, Prasad et al. (2007) noted the prevalence of taeniasis to be 18.6% in pig-farming communities in north India. Interventions in the community aimed at substantially reducing the rates of NCC infection can take several forms. It is essential to know the extent to which the population is exposed to the infecting organism when determining goals to control disease and prevent transmission. The exposure to NCC is not known in south India but can be determined from the seroprevalence of cysticercus antibodies in the community. To establish the level of exposure of the population in south India to T. solium, a serological study measuring cysticercus antibodies to infection-specific antigens was carried out in a district of the south Indian state of Tamil Nadu.
247
around 2500 randomly chosen from Kaniyambadi Block, with a population over 100 000 (82 village panchayats) experiencing similar social and cultural characteristics. In the urban areas, similar geographically demarcated areas are called wards (which come under the district municipality), and four wards were randomly selected out of >45 wards. In each of the 20 clusters, 20 families, assumed to be of four members each, were selected using a systematic sampling technique and a random start. The selected population of 1600 was 75% rural and 25% urban, to represent the distribution in the country. Information on pork consumption and living in a pig-rearing or non-pig-rearing region of a village or ward was obtained from all the population sampled. Between March 2004 and February 2005 blood (2—5 ml) was drawn from all consenting individuals and transported cold to the laboratory at the Christian Medical College, Vellore, within 4 h of collection. Serum was stored at −20 ◦ C until assay.
2.4. Cysticercus serology
2. Materials and methods 2.1. Study region The seroprevalence of cysticercus antibodies was determined in a rural and urban population of Vellore district, which is one of 30 districts in the state of Tamil Nadu, south India. The male:female ratio is nearly equal in Vellore district. The population of Tamil Nadu is 62 million and that of Vellore district 3.5 million. The rural population was from Kaniyambadi Block, an area of 182 km2 , 85 villages and 105 000 people. The urban population was 300 000 people from Vellore town. Kaniyambadi Block is a rural development block south of Vellore and has served as the field practice area of the Community Health Department for nearly 50 years. The Department provides comprehensive health and development services to the entire block, enabling good rapport with the community. Kaniyambadi Block and Vellore town border each other; they are connected by road and their populations intermingle. Agriculture and animal husbandry are the major occupations of the rural population, while pig rearing and pork consumption occur in both populations. The average literacy rate of Vellore town is 74% (male 80% and female 68%). The population under study is representative of the state of Tamil Nadu.
2.2. Study population The study population covered 50 617 people who had been screened for active epilepsy, of whom 38 105 were rural and 12 512 were urban (Rajshekhar et al., 2006).
2.3. Study design The seroprevalence of cysticercus antibodies was studied in people aged 2—60 years from 20 clusters. Rural clusters in the study are village panchayats (settlements of people with local self-governance), each with a population of
Cysticercus antibodies were determined in sera on immunoblots against lentil lectin-specific T. solium glycoproteins, as described by Prabhakaran et al. (2004). Sera were considered positive for cysticercus antibodies by the criteria of Tsang et al. (1989), i.e. reaction to one or more T. solium glycoproteins of molecular weights 50, 38—42, 24, 21, 18, 14 and 13 kDa. Blots were read independently by two laboratory personnel. The immunoblot detects antibodies to T. solium glycoproteins that are specific and diagnostic for cysticercosis. In this study, in a community that had been screened for active epilepsy/recent onset seizures and were asymptomatic, a positive immunoblot suggests silent NCC, systemic cysticercosis or a past infection and was taken as an index of exposure to T. solium.
2.5. Statistical analysis Data were analyzed for significant differences by the 2 test and were considered significant at P < 0.05.
3. Results Serology was determined in 1063 people who consented to provide blood, sampled from a population of 50 423 who were seizure-free (Rajshekhar et al., 2006): 84.4% of the samples were from the rural population and 15.6% from the urban population. The population seroprevalence of cysticercus antibodies was significantly higher in the rural population compared with the urban population among both men and women (Figure 1). People living in rural areas were three times more likely to be seropositive for cysticercus antibodies than their urban counterparts (P < 0.001). The prevalence of cysticercus antibodies was significantly higher in rural women than in rural men but did not differ between urban men and women (Figure 1). Stratified for age, seroprevalence was highest in young adults (16—45 years) and in young adult rural women (Figure 2).
248
V. Prabhakaran et al.
Figure 1
Seroprevalence of cysticercus antibodies to Taenia solium in Vellore district, south India.
in this study ate pork that had not been subjected to meat inspection.
4. Discussion A seroprevalence of nearly 16% for cysticercus antibodies in Vellore district, where one-third of all households have one or more members seropositive for the antibodies, is high and categorizes the district as hyperendemic for exposure to T. solium. The immunoblot used in this study under-reports infections with a single cyst (60% sensitive) (Prabhakaran et al., 2004), suggesting that the prevalence in Vellore district may be higher than stated. This is important, as almost one-third of all epilepsy in Vellore district is due to NCC (Rajshekhar et al., 2006). The high seroprevalence among adults of the district may reflect the known increased susceptibility to infection with age (Fleury et al., 2004). Although the population included in this study was seizurefree, seropositive individuals need follow-up to ensure that anyone with symptoms, particularly for NCC, seeks medical advice. A main finding of the study was the significantly higher seroprevalence in the rural population compared with the urban population. Reasons for this could be varied, with different sociocultural background and practices, of which the higher prevalence of consuming pork may also contribute. The higher seroprevalence in the rural population may also reflect poorer sanitation and therefore greater environmental fecal contamination in rural communities, although the proportion of rural and urban populations living in pigrearing areas were comparable in this study (60—63%). This
Figure 2 Age and seroprevalence of cysticercus antibodies in Vellore district, south India. : rural population; : urban population.
Blood samples from the rural population were obtained from 296 households in 16 clusters of 22 villages. Seroprevalence in these villages ranged from 3.2 to 42.6%. In 36.1% of the households, one or more members were positive for cysticercus antibodies (Table 1). Blood samples from the urban population were obtained from 52 households in four wards, where seroprevalence for cysticercus antibodies ranged from 0 to 15.9%. In 17.3% of these households, one or more members were positive for cysticercus antibodies (Table 1). The proportions of the urban and rural populations in this study living in pig-rearing areas of the town or village were 59.6 and 63.2%, respectively. Twelve percent of the urban population and 24.2% of the rural population sampled
Table 1
Distribution of cysticercus antibodies in Vellore district, south India
Population
No. sera
Cysticercus antibody seroprevalence (%)
No. households tested
% households with positive immunoblots ≥2 people
1 person
0 people
Rural Urban
897 166
17.7 6.0
296 52
13.2 1.9
22.9 15.4
63.9 82.7
Total
1063
15.9
348
11.5
21.8
66.7
Seroprevalence of Taenia solium antibodies in Vellore district, south India has been shown in other endemic areas (Fleury et al., 2006). Seropositivity in over one-third of all rural households, with 13% of the households having two or more members positive for cysticercus antibodies, would corroborate high environmental contamination with T. solium. Studies from Peru have noted increased seropositivity among contacts of tapeworm carriers (Garc´ıa et al., 2003a). Although seroprevalence is lower in the urban population of Vellore district, seropositivity in 17.3% of households in a population of 300 000 does indicate significant exposure to T. solium. The rural and urban areas of Vellore district studied are representative of living and environmental conditions in most of India, and it is probable that seroprevalence of T. solium antibodies is equally high in other parts of the country. This is borne out in studies by Khurana et al. (2006), who analyzed 600 sera by ELISA and found a seroprevalence of 17.3% for cysticercus antibodies in Chandigarh, north India. They also noted higher prevalence in rural (20%) compared with urban (8%) populations and, importantly, that the highest prevalence was among people who lived in close contact with pigs and who had poor sanitation and water facilities. Thus their study also suggests that in Indian communities there are pockets in the population from which T. solium infections may spread. As in the present study, they also noted high cysticercus antibody seroprevalence in women and attributed it to eating unwashed, raw vegetables while cooking. A seroprevalence of 15—17% in the general population in India is comparable to, and in several instances much higher than, that in countries endemic for T. solium cysticercosis and where it is determined by levels of T. solium in the environment. In other countries of Asia, seroprevalence ranges from 1.65% in Indonesia to 3.97—16.4% in China (Chung et al., 2005; Li et al., 2006; Sutisna et al., 1999). Studies from Viet Nam found circulating cyst antigen to range from 5.3% in mountainous rural regions to 0% in urban populations (Somers et al., 2006). In West Africa, Togo and Benin report seroprevalence at a conservative 2.4 and 1.3%, respectively (Zoli et al., 2003), while the levels in Burundi, Eastern/Central Africa are 30% (Nsengiyumva et al., 2003). In South America, population seroprevalence of cysticercus antibodies has been studied extensively, and ranges from 13.7% in the highlands to 24.2% on the coast in Peru (Montano et al., 2005). Seroprevalence in central—western Brazil is 11.3% and higher for those living in areas of poor sanitation (Oliveira et al., 2006); it is 5.6 and 2.1% in urban and rural Brazil, respectively (Bragazza et al., 2002; Silveira-Lacerda Ede et al., 2002). In rural Mexico, seroprevalence is reported at 3.7% (Rodriguez-Canul et al., 1999). These seroprevalence studies provide evidence that populations in large parts of the world are exposed to T. solium. Although exposure to T. solium per se does not translate into infection, as up to 40% of people seropositive for T. solium do not develop the infection (Fleury et al., 2006; Meza-Lucas et al., 2003), a population seroprevalence of 16% for cysticercus antibodies emphasizes the pervasiveness of T. solium in Vellore district. Future studies need to determine risk of occupation (pig rearing) and importance of humanto-human egg transmission on cysticercus seropositivity, as the high index of exposure to T. solium, with its origins in poor animal husbandry and sanitation, is clearly of public health concern in India.
249
Authors’ contributions: VR, JM and AO designed the study and drafted the manuscript; VP carried out all laboratory work; MVR carried out the community studies. All authors analyzed the data and read and approved the final manuscript. AO, VR and JM are guarantors for the paper. Acknowledgements: The authors thank G. George Martin, J. Vijayakumar, N. Arulraj, N. Ethiraj and P. Babu for their expert assistance in collecting and processing blood samples. Funding: The study was supported in part by a Task Force grant from the Indian Council of Medical Research, New Delhi, India (D.O.No. SWG/Neuro/3/2001-NCD-1). Conflicts of interest: None declared. Ethical approval: Institutional Review Board of the Christian Medical College, Vellore, India (R.C. Min No 4638).
References Bragazza, L.M., Vaz, A.J., Passos, A.D., Takayanagui, O.M., Nakamura, P.M., Espindola, N.M., Pardini, A., Bueno, E.C., 2002. Frequency of serum anti-cysticercus antibodies in the population of a rural Brazilian community (Cassia dos coqueiros, SP) determined by Elisa and immunoblotting using Taenia crassiceps antigens. Rev. Inst. Med. Trop. Sao Paulo 44, 7—12. Chung, J.Y., Eom, K.S., Yang, Y., Li, X., Feng, Z., Rim, H.J., Cho, S.Y., Kong, Y., 2005. A seroepidemiological survey of Taenia solium cysticercosis in Nabo, Guangxi Zhuang Autonomous Region, China. Korean J. Parasitol. 43, 135—139. Fleury, A., Dessein, A., Preux, P.M., Dumas, M., Tapia, G., Larralde, C., Sciutto, E., 2004. Symptomatic human neurocysticercosis—– age, sex and exposure factors relating with disease heterogeneity. J. Neurol. 251, 830—837. Fleury, A., Morales, J., Bobes, R.J., Dumas, M., Y˜ anez, O., Pi˜ na, J., Carrillo-Mezo, R., Martinez, J.J., Fragoso, G., Dessein, A., Larralde, C., Sciutto, E., 2006. An epidemiological study of familial neurocysticercosis in an endemic Mexican community. Trans. R. Soc. Trop. Med. Hyg. 100, 551—558. Garc´ıa, H.H., Gilman, R.H., Gonzalez, A.E., Verastegui, M., Rodriguez, S., Gavidia, C., Tsang, V.C., Falcon, N., Lescano, A.G., Moulton, L.H., Bernal, T., Tovar, M., Cysticercosis Working Group in Peru, 2003a. Hyperendemic human and porcine Taenia solium infection in Peru. Am. J. Trop. Med. Hyg. 68, 268—275. Garc´ıa, H.H., Gonzalez, A.E., Carlton, A.W., Evans, C.A.W., Gilman, R.H., 2003b. Taenia solium cysticercosis. Lancet 362, 547—556. Khurana, S., Aggarwal, A., Malla, N., 2006. Prevalence of anticysticercus antibodies in slum, rural and urban populations in and around Union territory, Chandigarh. Indian J. Pathol. Microbiol. 49, 51—53. Li, T., Craig, P.S., Ito, A., Chen, X., Qiu, D., Qiu, J., Sato, M.O., Wandra, T., Bradshaw, H., Li, L., Yang, Y., Wang, Q., 2006. Taeniasis/cysticercosis in a Tibetan population in Sichuan Province, China. Acta Trop. 100, 223—231. Meza-Lucas, A., Carmona-Miranda, L., Garc´ıa-Jeranimo, R.C., Torrero-Miranda, A., Gonzalez-Hidalgo, G., Lapez-Castellanos, G., Correa, D., 2003. Short report: limited and short-lasting humoral response in Taenia solium: seropositive households compared with patients with neurocysticercosis. Am. J. Trop. Med. Hyg. 69, 223—227. Montano, S.M., Villaran, M.V., Ylquimiche, L., Figueroa, J.J., Rodriguez, S., Bautista, C.T., Gonzalez, A.E., Tsang, V.C., Gilman, R.H., Garcia, H.H., Cysticercosis Working Group in Peru,
250 2005. Neurocysticercosis: association between seizures, serology, and brain CT in rural Peru. Neurology 65, 229—233. Nsengiyumva, G., Druet-Cabanac, M., Ramanankandrasana, B., Bouteille, B., Nsizabira, L., Preux, P.M., 2003. Cysticercosis as a major risk factor for epilepsy in Burundi, East Africa. Epilepsia 44, 950—955. Oliveira, H.B., Rodrigues, R.M., Barcelos, I.S., Silva, L.P., CostaCruz, J.M., 2006. Anti-Taenia solium metacestode IgG antibodies in serum samples from inhabitants of a central-western region of Brazil. Rev. Inst. Med. Trop. Sao Paulo 48, 49—52. Prabhakaran, V., Rajshekhar, V., Murrell, K.D., Oommen, A., 2004. Taenia solium metacestode glycoproteins as diagnostic antigens for solitary cysticercus granuloma in Indian patients. Trans. R. Soc. Trop. Med. Hyg. 98, 478—484. Prasad, K.N., Chawla, S., Jain, D., Pandey, C.M., Pal, L., Pradhan, S., Gupta, R.K., 2002. Human and porcine Taenia solium infection in rural north India. Trans. R. Soc. Trop. Med. Hyg. 96, 515—516. Prasad, K.N., Prasad, A., Gupta, R.K., Pandey, C.M., Singh, U., 2007. Prevalence and associated risk factors of Taenia solium taeniasis in a rural pig farming community of north India. Trans. R. Soc. Trop. Med. Hyg., 101. Rajshekhar, V., Raghava, M.V., Prabhakaran, V., Oommen, A., Muliyil, J., 2006. Active epilepsy as an index of burden of neurocysticercosis in Vellore district, India. Neurology 67, 2135—2139.
V. Prabhakaran et al. Rodriguez-Canul, R., Fraser, A., Allan, J.C., Dominguez-Alpizar, J.L., Argaez-Rodriguez, F., Craig, P.S., 1999. Epidemiological study of Taenia solium taeniasis/cysticercosis in a rural village in Yucatan state, Mexico. Ann. Trop. Med. Parasitol. 93, 57—67. Silveira-Lacerda Ede, P., Machado, E.R., Arantes, S.C., Costa-Cruz, J.M., 2002. Anti-Taenia solium metacestodes antibodies in serum from blood donors from four cities of Tri˜ angulo Mineiro area, Minas Gerais, Brazil, 1995. Rev. Inst. Med. Trop. Sao Paulo 44, 229—231. Somers, R., Dorny, P., Nguyen, V.K., Dang, T.C., Goddeeris, B., Craig, P.S., Vercruysse, J., 2006. Taenia solium taeniasis and cysticercosis in three communities in north Vietnam. Trop. Med. Int. Health 11, 65—72. Sutisna, I.P., Fraser, A., Kapti, I.N., Rodriguez-Canul, R., Puta Widjana, D., Craig, P.S., Allan, J.C., 1999. Community prevalence study of taeniasis and cysticerosis in Bail, Indonesia. Trop. Med. Int. Health 4, 288—294. Tsang, V.C., Brand, J.A., Boyer, A.E., 1989. An enzyme-linked immunoelectrotransfer blot assay and glycoprotein antigens for diagnosing human cysticercosis Taenia solium. J. Infect. Dis. 159, 50—59. Zoli, A., Shey-Njila, O., Assana, E., Nguekam, J.P., Dorny, P., Brandt, J., Geerts, S., 2003. Regional status, epidemiology and impact of Taenia solium cysticercosis in Western and Central Africa. Acta Trop. 87, 35—42.