- Email: [email protected]
Epizootiological importance of Glossina morsitans submorsitans (Diptera: Glossinidae) (Newstead) in the Ghibe River Valley, Southwest Ethiopia
Acta Tropica 102 (2007) 100–105
Epizootiological importance of Glossina morsitans submorsitans (Diptera: Glossinidae) (Newstead) in the Ghibe River Valley, Southwest Ethiopia Merid Negash a,∗ , Melaku Girma b , Emiru Seyoum a b
a Addis Ababa University, Department of Biology, P.O. Box 1176, Addis Ababa, Ethiopia International Center of Insect Physiology and Ecology (Ethiopia), P.O. Box 17319, Addis Ababa, Ethiopia
Received 28 August 2006; received in revised form 19 March 2007; accepted 9 April 2007 Available online 13 April 2007
Abstract The epizootiological importance of Glossina morsitans submorsitans in Ghibe River Valley was undertaken from October 2000 to September 2001. The flies were collected using baited monoconical traps. G. m. submorsitans occurred with a mean apparent density of 4.26 ± 0.49 flies/trap/day and the apparent density was characterized by an increase during the wet season and a decrease during the dry season. Among 450 G. m. submorsitans, approximately 5% were found to be infected with trypanosome. Of these infected flies, 76% were female. Nanomonas, Duttonella and Trypanozoon were the three trypanosome subgenera detected and occurred in the proportions of 57.1%, 38.1% and 4.8%, respectively. Among 139 blood meals of G. m. submorsitans collected, 54.68% were identified to group or species levels. Accordingly, 36.84%, 25%, 11.84% and 10.53% accounted for cattle, kudu, suidae (warthog and/or wild pig) and human, respectively and others such as goats (6.58%), bovidae (5.26%), baboon (2.63%) and water buck (1.32%). While 21.05% of the blood meals were found to be out of detection range. © 2007 Elsevier B.V. All rights reserved. Keywords: G. m. submorsitans; Epizootiological importance; Ethiopia; Ghibe Valley
1. Introduction Agriculture is the mainstay of Ethiopian economy. The agricultural system is not mechanized; therefore, livestock play a crucial role in agricultural production both directly as food sources and as a source of traction power. Trypanosomosis is a major constraint in the health and productivity of livestock and hence agricultural production in Ethiopia in general. Annual estimated losses for Ethiopia as a result of trypanosomosis is roughly
∗ Corresponding author. Tel.: +251 911178908; fax: +251 111239471. E-mail address: [email protected] ( Merid Negash).
0001-706X/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.actatropica.2007.04.004
US$ 200 million, in terms of mortality and morbidity losses in livestock (denying utilization of fertile land for crop and livestock production) and the costs included in controlling the disease (IAEA, 1996). Between 150,000 and 200,000 km2 of otherwise agriculturally productive land mass is estimated to be infested by five different species of tsetse flies including, Glossina morsitans submorsitans (Newstead), Glossina pallidipes (Austen), Glossina tachinoides (Westood), Glossina fuscipes fuscipes (Newstead) and Glossina longipennis (Corti) (ISCTR, 1999). G. m. submorsitans is the most widely spread species in the country (Hutchinson, 1971) and it is likely that this species is the most important vector. In southwest Ethiopia, historical evidence suggests that an advance of G. m. submorsitans
Merid Negash et al. / Acta Tropica 102 (2007) 100–105
was responsible for a decrease in the area cultivated and an associated decrease in the area occupied by settlers (Reid et al., 1997). Three species of tsetse flies are found in Ghibe Valley where the present study was carried out, i.e. G. f. fuscipes, G. pallidipes and G. m. submorsitans (Fuller, 1978; Leak and Woudyalew, 1993). In Ghibe Valley, farmers claimed that a recent increase in trypanosomosis severity caused significant reduction in livestock population, farm land and milk production. From the previous studies by Leak et al. (1993) G. pallidipes and G. f. fuscipes feed mainly on livestock and G. pallidipes was the main vector of animal trypanosomosis, however, there are no data available for G. m. submorsitans as this species is a recent occurrence in the area (Leak et al., 1993). According to Ovazza (1956) only G. f. fuscipes was detected in the Ghibe Valley, similarly Ford et al. (1976) detected only G. f. fuscipes. However, a recent survey before Leak et al. (1993) done by Fuller (1978) detected both G. f. fuscipes and G. pallidipes, but not G. m. submorsitans. Understanding the target insect apparent density, host preference and infection rate could contribute towards management strategies. The main objectives of this study were to estimate the apparent density, infection rate and host preference of G. m. submorsitans in Ghibe River Valley. 2. Materials and methods 2.1. Description of the study area The study was undertaken in the Ghibe Valley in Southwest Ethiopia (Fig. 1). The area, in which the present study took place, is locally known as “Medale”. The climate is tropical with two rainfall periods per year. The main rainy season occurs from May to September, while the shorter season occurs from March to April. The area received 631.2 mm of rainfall during the study period. The average annual maximum temperature was 30.7 ◦ C while the minimum was 12.4 ◦ C for the study period (Merid et al., 2004). Most parts of the land are covered with open savanna grassland. The dominant tree species are Acacia seyal, Acacia sieberiana, and Acacia tortilis. The grasses most encountered in the area are Hyperanium spp. and Sorghum spp. There are 876 zebu cattle, 606 sheep and 337 goats. The human population in the area is 641 (283 male and 358 female). The main activity of the local people is farming. Three species of tsetse were encountered in the study area G. m. submorsitans, G. pallidipes and G. f. fuscipes.
101
Fig. 1. Location map (modified Leak et al., 1993) of the study site in the Ghibe River Valley, Ethiopia.
Sampling of the target tsetse flies was made from October 2000 up to September 2001. Sampling was taken for five consecutive days in each month. Six odour baited monoconical traps (Laveissiere and Grebaut, 1990) were used to sample flies. The distance between each trap was 200 m. The bait was acetone plus cow urine, with the release rate of 500–600 mg/h for acetone and 1–1.2 g/h for cow urine (Vale et al., 1988). Sampling was made from all possible tsetse habitats including habitats along the Ghibe River and in open savanna 10 kms apart from the river. Each sampling point was marked with dyed wooden poles for consecutive sampling. The apparent density, which often expressed as the number of tsetse caught per trap per day (flies/(trap day)) of G. m. submorsitans was estimated using a method described by Rogers (1983). Tsetse population density is less variable than those of many other insects. Thus field estimates of apparent density can be used for estimating disease risk. Infection rate in tsetse flies was determined through dissection (Lloyd and Johnson, 1924). This method involves the examination of salivary glands, proboscis and mid gut for infection by trypanosomes. Accordingly, when trypanosome infection was found only in the proboscis, it was considered to be Duttonella, whereas when found both in the proboscis and mid gut, it was
102
Merid Negash et al. / Acta Tropica 102 (2007) 100–105
considered to be Nanomonas and similarly when found in salivary gland it was considered to be Trypanozoon (Lloyd and Johnson, 1924). From trapped flies, those fed once were selected for blood meal identification. The abdomen was cut off using a clean scalpel and clean forceps. The blood filled gut was pulled out of the abdomen on to the Whatman No. 1 filter paper which was labeled into eight sections using pencil. The blood was then smeared on to the filter paper; air dried and kept in a desiccator. The blood specimens were sent to ICIPE Nairobi, Kenya for analysis using enzyme linked immunosorbent assay (ELISA) (Service et al., 1986). The range of conjugates tested included: baboon, bovidae, bush buck, bush pig, cattle, camel, chicken, crocodile, dog, goat, grants gazelle, hippopotamus, human, kudu, lion, ostrich, rhino, sheep, Thomson’s gazelle, warthog, water buck. 3. Statistical analysis The monthly variation in tsetse density was analyzed using Kruskal–Wallis H analysis of variance, followed by Mann–Whitney U test. Infection rate between male and female as well as between the different parasites were subjected to Chi-square test. The statistical package used was SPSS Version 10.00 for windows (SPSS Inc., 1999). 4. Results G. m. submorsitans occurred with a mean apparent density of 4.26 ± 0.49 flies/trap/day. The apparent density result elucidates a significant variation between months (P < 0.0001) (Fig. 2). Apparent density decreased during the dry months except on January and increased from May (start of rain) until it attained its peak in October (beginning of the dry months) after which it again decreased sharply in November. From 450 G. m. submorsitans examined for infection rate determination, 4.7% of the flies harbored trypanosome (Table 1). Of the infected flies, 76% were
Fig. 2. Monthly mean trap catch of Glossina morsitans submorsitans in Ghibe River Valley, Southwest Ethiopia (2000–2001). The same letters within each series indicate values that are not different according to nonparametric Kruskal–Wallis analyses of variance followed by a paired Mann–Whitney U test.
female while 24% were male. The difference was found to be significant (χ2 , 5.762 P = 0.016). The trypanosomes encountered belong to Nanomonas, Duttonella and Trypanozoon subgenus and occurred in the proportions of 54.14%, 38.1% and 4.76%, respectively. More flies were infected with Nanomonas than Trypanozoon. Similarly more flies were infected by Duttonella than Trypanozoon. The variation was statistically significant χ2 , 9.308, d.f. = 1, P = 0.002 and χ2 , 5.444, d.f. = 1, P = 0.02, respectively. However, no significant difference was observed between Nanomonas and Duttonella (χ2 , 0.8, d.f = 1, P = 0.371). From a total of 139 blood samples collected, 76 (54.68%) samples were confirmed to be host blood. Among these hosts, 36.84% of meals were obtained from cattle, 25% from Kudu. Suidae (warthog and/or wild pig) made about 11.84% of the meals, human beings made about 10.53%, goat about 6.58%, bovidae about 5.26% (which refers to any wild ruminant in the bovidae family excluding those listed among the conjugates), 2.63% of the meals was taken from baboon and 1.32% was taken
Table 1 Infection rate in male and female G. m. submorsitans and percentage composition of trypanosome subgenus identified in Ghibe River Valley, Southwest Ethiopia (2000–2001) Trypanosome subgenus
Male (194)
Female (256)
Total
Percentage of trypanosome subgenus
Nanomonas Duttonella Trypanozoon Total trypanosomes infected Trypanosome infection rate (%)
3 2 0 5 2.6
9 6 1 16 6.25
12 8 1 21 4.7
57.1 38.1 4.8
Number in parenthesis is total tsetse flies checked for infection.
Merid Negash et al. / Acta Tropica 102 (2007) 100–105
Fig. 3. Host preference of G. m. submorsitans in Ghibe River Valley, Southwest Ethiopia (2000–2001).
from water buck/Reedbuck (Fig. 3). Sixteen (21.05%) of the blood meal samples collected were unidentified, i.e. were not within the host range available. 5. Discussion The observed pattern of fluctuation in apparent density (Fig. 2) showed that G. m. submorsitans was most abundant during the rainy months. This result is in agreement with previous works on seasonality of G. m. submorsitans in other parts of Africa (Snow, 1981; Getachew, 1983). However, environmental, as well as biological factors, may attribute for high number flies caught in January. There was a shower of rain in January, which might have reduced adult mortality in that month (Merid et al., 2004). The infection rate of G. m. submorsitans was found to be low for morsitans when compared to 15–20% infection rate obtained by other researchers (Glasgow, 1963; Ford, 1971; FAO, 1982). Since the dissection methods lacks sensitivity and unable to detect mixed infection as opposed to more sensitive methods such as PCR and dotELISA (Morlais et al., 1998; Ouma et al., 2000; Solano et al., 2001) that could be main reason for low infection rate. The present results are different from previous findings by Getachew (1983) and Habtamu (1993), who had done similar work on the same species at Fincha and Didessa valleys (western Ethiopia) and who obtained 0.5% and 2.65% infection rate, respectively. This may be due to the difference in feeding habit of G. m. submorsitans in the two areas, because, according to Jordan (1965), tsetse flies feeding on domestic or wild bovidae are more likely to be infected than those feeding on suids.
103
From the present study, a greater number of G. m. submorsitans was infected with Nanomonas. According to Ford (1971) in East Africa, it is generally found that when morsitans are vectors of Trypanosoma vivax and Trypanosoma congolense, the later is usually the dominant trypanosome. Since G. m. submorsitans and G. pallidipes are found in the area this may be one of the reasons for the Nanomonas predominance. T. congolense is the predominant trypanosome in cattle populations within or close to the infestation of Glossina (Jordan, 1986). As the distance from known tsetse infestation increase Trypanosoma vivax becomes more frequent and eventually predominant in cattle. Since this study was done in the main infestation area this may be one of the reasons for the higher percentage of Nanomonas. Similarly, according to Moloo et al. (2000) who demonstrated that tsetse flies feed more successfully on cattle infected with T. congolense than on cattle infected with T. vivax this could also contribute for Nanomonas dominance. Farmers in the study area extensively use trypanocidal drugs to treat their cattle. T. congolense was found to be more resistant to the available drugs, diminazene aceturate, isometamidium chloride and homidium chloride in the area (Codjia et al., 1993). The drugs used may have greatly reduced the incidence of susceptible Duttonella, enabling resistant Nanomonas to become predominant. Female G. m. submorsitans were found to be more infected than males (Table 1), which agrees with previous works (Glasgow, 1963). Although it is difficult to generalize, this may be because females live longer and feed more frequently than males, thus having greater chances to feed on infected hosts. The three detected parasites in G. m. submorsitans make it epizootiologically very important, since Nanomonas and Duttonella cause very serious disease in cattle. Trypanozoon causes very serious disease in horses and donkeys, which may be the main reason for the exclusion of donkeys and horses in the area (even though it needs further investigation), which seriously affects the livelihood and activity of the people living in the area, since these animals are very important for transportation and traction. In the area, there is movement of cattle to reach new grazing ground (especially during the dry season) and markets. This movement can aggravate the spread of trypanosomosis both within the infected area and into areas known to be outside the tsetse belt. In the latter case, it is mainly due to mechanical transmission. The distribution and abundance, of Glossina spp. is closely associated with the presence and distribution of their hosts. It was difficult to collect enough engorged flies as stationary traps catch hungry flies, which seek
104
Merid Negash et al. / Acta Tropica 102 (2007) 100–105
host to feed. But it was possible to collect 139 blood meal samples. From the present investigation, cattle were found to be the most preferred host followed by kudu (Fig. 3). In areas where cattle are restricted, like in dense forests, G. m. submorsitans feed more on warthog. According to Snow and Borham (1979); who carried out their study in the West Kiang of Gambia where cattle are very restricted in their contact with woodland areas (a preferred habitat of G. m. submorsitans) 90% blood source of G. m. submorsitans was obtained from warthog. According to Clausen et al. (1998) 57.1% of meal of G. m. submorsitans was derived from Suidae in which warthog accounts 37%. Warthog is one of the reliable hosts of tsetse (Nash, 1969) having a relatively restricted home range in favoured tsetse habitats and being most active in the early morning and late afternoon when tsetse are active too (Torr, 1994). Similarly, Habtamu (1993) reported that 52.9% of G. m. submorsitans meal was from warthog. Moloo (1993) has summarized the hosts of the different tsetse species and the order of host preference for G. m. submorsitans goes as warthog, human, and cattle, respectively. In East Africa, where bovids are abundant, G. m. submorsitans feed less on warthog than in areas where wild bovidae are relatively scarce (Jordan et al., 1962). Moreover, the epidemiology of vector borne diseases is complex and related to the ecology of host, vectors and parasites (de La Rocque et al., 2005). The present result agrees with this explanation where cattle followed by kudu were the preferred host of G. m. submorsitans. Therefore, kudu might be the main wild animal host that supports the tsetse population in the area and the reservoir of the three pathogens detected in G. m. submorsitans. However, the role of other wild hosts should not be undermined especially the suids as they are highly infected by trypanosomes (Hoare, 1972). Human beings were also found to be host of G. m. submorsitans in the area. The activities of the people are predominantly production of charcoal as fuel source, and collecting honey as a means of complimentary income. There is also a footpath through which people from other areas cross this tsetse belt to reach the market place. These activities might have created a close contact between tsetse and human beings. Therefore, G. m. submorsitans could also be epidemiologically important by transmitting the zoonotic (Rhodesian) human trypanosomosis if infected animal, human or reservoir game animals are introduced in to the region accidentally. The blood meals (21.05%) which were out of detection range may be taken from hosts that were not included in the conjugate for the blood meal analysis.
Acknowledgements The work was sponsored by the African Regional Postgraduate Program in Insect Sciences (ARPPIS), we also thank Addis Ababa University Department of Biology and ICIPE, Ethiopia (especially Dr. Getachew Tikubet), for logistic and technical support. Vestergaard Frandsen Group is acknowledged for providing experimental traps. ILRI’s Ghibe research station is equally appreciated allowing us to use their laboratory facilities. Comments given by the three anonymous reviewers were both useful and encouraging for which we are grateful.
References Clausen, P.H., Adeyemi, I., Bauer, B., Breloeer, M., Salchow, F., Staak, C., 1998. Host preferences of tsetse based on blood meal identifications. Med. Vet. Entomol. 12, 169–180. Codjia, V., Woudyalew, M., Majiwa, P.A.O., Leak, S.G.A., Rowlands, G.J., Authie, E., d’Iteren, G.D.M., Peregrine, A.S., 1993. Occurrence of populations of Trypanosoma congolense resistant to diminazene, isometamidium and homidium in the Ghibe Valley, Southwest Ethiopia. Acta Trop. 53, 151–163. de La Rocque, S., Michel, J.F., Bouyer, J., De Wispelaere, G., Cuisance, D., 2005. Geographical information systems in parasitology: a review of potential applications using the example of animal trypanosomosis in West Africa. Parasitology 47, 97–104. FAO, 1982. In: Pollock, J.N. (Ed.), Tsetse Control Training Manual, vol. 1. Tsetse Biology, Systematic and Distribution, Techniques. Food and Agriculture Organization of the United Nations, Rome, p. 280. Ford, J., 1971. The Role of Trypanosomiasis in African Ecology. A Study of Tsetse Fly Problem. Clarendon press, Oxford, p. 568. Ford, J., Makin, M.J., Grimble, R.J., 1976. Trypanosomiasis Control Programme for Ethiopia. Report to the Ethiopian Government of the British Technical Assistance Team appointed to determine a programme for tsetse fly and trypanosomiasis control and subsequent land use in south-western Ethiopia. Ministry of Overseas Development of Great Britain, p. 127. Fuller, G.K., 1978. Distribution of Glossina in South Western Ethiopia. Bull. Ent. Res. 68, 299–302. Getachew, T., 1983. Studies on tsetse flies of Finchaa River Valley. MSc Thesis. A.A. University School of Graduate Studies, 83 pp. Glasgow, J.P., 1963. The Distribution and Abundance of Tsetse. Pergmon Press, Oxford, p. 241. Habtamu, B., 1993. Host, trap and odour bait preference determination of tsetse flies (G. m. submorsitans) in the upper Didessa Valley Southwest Ethiopia. MSc Thesis. A.A. University School of graduate Studies, 65 pp. Hoare, C.A., 1972. The Trypanosomes of Mammals. Blackwell Scientific Publications, Oxford, p. 749. Hutchinson, M.P., 1971. Human trypanosomiasis in Southwest Ethiopia. Ethiopia Med. J. 9, 3–69. IAEA, 1996. Government of Federal Democratic Republic of Ethiopia Draft Projects Document Integrating the Sterile Insect Technique to Eradicate tsetse from the Southern rift Valley of Ethiopia. December.
Merid Negash et al. / Acta Tropica 102 (2007) 100–105 International Scientific Council for Trypanosomosis Research and control (ISCTRC), 1999. Proceedings of the ISCTRC 24th Meeting. pp. 77–81. OAU/STRC Publication, Maputo, no. 119. Jordan, A.M., 1965. Long-term fluctuations in numbers of a population of Glossina sixteen years observations. In: Proceedings of the 10th Meeting. International Scientific Committee for Trypanosomiasis Research. Kampala, 24–28 October, 1964, pp 85–90. Commission for Technical Co-operation in Africa, Lagos (Publication no.97). Jordan, A.M., 1986. Trypanosomiasis Control and African Rural Development. Longman, London, p. 357. Jordan, A.M., Jones, F.L., Weitz, B., 1962. The natural hosts of tsetse flies in northern Nigeria. Ann. Trop. Med. Parasitol. 56, 430–442. Laveissiere, C., Grebaut, P., 1990. recherches sur les pieges a Glossines (Diptera: Glossinidae) mise au point d’un mode’le economique le piege ‘Vavoua’. Trop. Med. Parasitol. 41, 185–192. Leak, S.G.A., Woudyalew, M., 1993. Advance of Glossina morsitans submorsitans and Glossina pallidipes along the Ghibe river system in southwest Ethiopia. Acta Trop. 55, 91–95. Leak, S.G.A., Woudyalew, M., Authie, E.d’Ieteren, Peregrine, A.S., Rowlands, G.J., Trail, J.C.M., 1993. Epidemiology of bovine trypanosomiasis in the Ghibe Valley, southwest Ethiopia. Tsetse challenge and its relationship to trypanosome prevalence in cattle. Acta Trop. 53, 121–134. Lloyd, L., Johnson, W.B., 1924. The trypanosome infections of tsetse flies in northern Nigeria and a new method of estimation. Bull. Ent. Res. 14, 265–288. Merid, N., Melaku, G., Emiru, S., 2004. Seasonality and diel activity pattern of Glossina morsitans submorsitans in Ghibe River Valley. SINET: Ethiop. J. Sci. 27 (2), 135–142. Moloo, S.K., 1993. The distribution of Glossina species in Africa and their natural hosts. Insect Sci. Appl. 4, 511–527. Moloo, S.K., Sabwa, C.L., Baylis, M., 2000. Feeding behaviour of Glossina pallidipes and G. morsitans centralis on Boran cattle infected with Trypanosoma congolense or T.vivax under laboratory conditions. Med. Vet. Entomol. 14, 290–299. Morlais, I., Grebaut, P., Bodo, J.M., Djoha, S., Cuny, G., Herder, S., 1998. Detection and identification of trypanosomes by polymerase chain reaction in wild tsetse flies in Cameroon. Acta Trop. 70, 109–117. Nash, T.A.M., 1969. The tsetse fly. In: African Bane. Collins Clear Tepe Press, London, p. 215.
105
Ouma, J.O., Masake, R.A., Masiga, D.K., 2000. Comparative sensitivity of dot-ELISA. PCR and dissection method for the detection of trypanosome infections in tsetse flies (Diptera: Glossinidae). Acta Trop. 75, 315–321. Ovazza, M., 1956. Contribution a 1’eiude des dipteres vulnerants de 1’empire d’Ethiopie IV. Glossina. Bull. Soc. Path. Exot. 49, 204–209. Reid, R.S., Kruska, R.L., Muthui, N., Wotton, S., Wilson, C.J., Andualem, T., Woudyalew, M., 1997. Distinguishing the impacts of change in trypanosomiasis severity from other factors that cause land use change over time in southwestern Ethiopia. In: Proceedings of the 24th Meeting of the International Scientific Council for Trypanosomosis Research and Control, Maputo, Mozambique. Rogers, D.J., 1983. Trypanosomiasis ‘Risk or challenge’: a review with recommendations livestock productivity and trypanotolerance. In: Network Training Manual. ILCA Addis Ababa, Ethiopia, pp. 101–127. Service, M.W., Voller, A., Bidwell, D.E., 1986. The enzyme-linked immunosorbent assay (ELISA) test for the identification of bloodmeals of haematophagous insects. Bull. Ent. Res. 76, 321– 330. Snow, W.F., 1981. Tsetse ecology and epidemiology of trypanosomiasis in the Gambia and on the south Kenya coast: a comparison. In: Proceedings of the 16th Meeting International Scientific Council for Trypanosomiasis Research. Yaound´e, 1979, pp. 369–381. Organization of African Unity, Scientific and Technical Research Commission (Publication no. 111). Snow, R.K., Borham, P.F.L., 1979. The feeding and ecology of tsetse fly Glossina m. submorsitans in relation to nagana transmission in Gambia. Acta Trop. 36, 47–51. Solano, P., Guegan, J.F., Reifenberg, J.M., Thomas, F., 2001. Trying to predict and explain the presence of African trypanosomes in tsetse flies. J. Parasitol. 87, 1058–1063. SPSS Inc., 1999. SPSS for Windows Version 10.00. SPSS Inc., Chicago. Torr, S.J., 1994. Responses of tsetse flies (Diptera: Glossinidae) to warthog (Phacochoerus aethiopicus Pallas). Bull. Ent. Res. 66, 713–729. Vale, G.A., Hall, D.R., Gough, T.A.E., 1988. The olfactory response of tsetse flies. Glossina spp. (Diptera: Glossinidae) to phenols and urine in the field. Bull. Ent. Res. 78, 293–300.
Epizootiological importance of Glossina morsitans submorsitans (Diptera: Glossinidae) (Newstead) in the Ghibe River Valley, Southwest Ethiopia Merid Negash a,∗ , Melaku Girma b , Emiru Seyoum a b
a Addis Ababa University, Department of Biology, P.O. Box 1176, Addis Ababa, Ethiopia International Center of Insect Physiology and Ecology (Ethiopia), P.O. Box 17319, Addis Ababa, Ethiopia
Received 28 August 2006; received in revised form 19 March 2007; accepted 9 April 2007 Available online 13 April 2007
Abstract The epizootiological importance of Glossina morsitans submorsitans in Ghibe River Valley was undertaken from October 2000 to September 2001. The flies were collected using baited monoconical traps. G. m. submorsitans occurred with a mean apparent density of 4.26 ± 0.49 flies/trap/day and the apparent density was characterized by an increase during the wet season and a decrease during the dry season. Among 450 G. m. submorsitans, approximately 5% were found to be infected with trypanosome. Of these infected flies, 76% were female. Nanomonas, Duttonella and Trypanozoon were the three trypanosome subgenera detected and occurred in the proportions of 57.1%, 38.1% and 4.8%, respectively. Among 139 blood meals of G. m. submorsitans collected, 54.68% were identified to group or species levels. Accordingly, 36.84%, 25%, 11.84% and 10.53% accounted for cattle, kudu, suidae (warthog and/or wild pig) and human, respectively and others such as goats (6.58%), bovidae (5.26%), baboon (2.63%) and water buck (1.32%). While 21.05% of the blood meals were found to be out of detection range. © 2007 Elsevier B.V. All rights reserved. Keywords: G. m. submorsitans; Epizootiological importance; Ethiopia; Ghibe Valley
1. Introduction Agriculture is the mainstay of Ethiopian economy. The agricultural system is not mechanized; therefore, livestock play a crucial role in agricultural production both directly as food sources and as a source of traction power. Trypanosomosis is a major constraint in the health and productivity of livestock and hence agricultural production in Ethiopia in general. Annual estimated losses for Ethiopia as a result of trypanosomosis is roughly
∗ Corresponding author. Tel.: +251 911178908; fax: +251 111239471. E-mail address: [email protected] ( Merid Negash).
0001-706X/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.actatropica.2007.04.004
US$ 200 million, in terms of mortality and morbidity losses in livestock (denying utilization of fertile land for crop and livestock production) and the costs included in controlling the disease (IAEA, 1996). Between 150,000 and 200,000 km2 of otherwise agriculturally productive land mass is estimated to be infested by five different species of tsetse flies including, Glossina morsitans submorsitans (Newstead), Glossina pallidipes (Austen), Glossina tachinoides (Westood), Glossina fuscipes fuscipes (Newstead) and Glossina longipennis (Corti) (ISCTR, 1999). G. m. submorsitans is the most widely spread species in the country (Hutchinson, 1971) and it is likely that this species is the most important vector. In southwest Ethiopia, historical evidence suggests that an advance of G. m. submorsitans
Merid Negash et al. / Acta Tropica 102 (2007) 100–105
was responsible for a decrease in the area cultivated and an associated decrease in the area occupied by settlers (Reid et al., 1997). Three species of tsetse flies are found in Ghibe Valley where the present study was carried out, i.e. G. f. fuscipes, G. pallidipes and G. m. submorsitans (Fuller, 1978; Leak and Woudyalew, 1993). In Ghibe Valley, farmers claimed that a recent increase in trypanosomosis severity caused significant reduction in livestock population, farm land and milk production. From the previous studies by Leak et al. (1993) G. pallidipes and G. f. fuscipes feed mainly on livestock and G. pallidipes was the main vector of animal trypanosomosis, however, there are no data available for G. m. submorsitans as this species is a recent occurrence in the area (Leak et al., 1993). According to Ovazza (1956) only G. f. fuscipes was detected in the Ghibe Valley, similarly Ford et al. (1976) detected only G. f. fuscipes. However, a recent survey before Leak et al. (1993) done by Fuller (1978) detected both G. f. fuscipes and G. pallidipes, but not G. m. submorsitans. Understanding the target insect apparent density, host preference and infection rate could contribute towards management strategies. The main objectives of this study were to estimate the apparent density, infection rate and host preference of G. m. submorsitans in Ghibe River Valley. 2. Materials and methods 2.1. Description of the study area The study was undertaken in the Ghibe Valley in Southwest Ethiopia (Fig. 1). The area, in which the present study took place, is locally known as “Medale”. The climate is tropical with two rainfall periods per year. The main rainy season occurs from May to September, while the shorter season occurs from March to April. The area received 631.2 mm of rainfall during the study period. The average annual maximum temperature was 30.7 ◦ C while the minimum was 12.4 ◦ C for the study period (Merid et al., 2004). Most parts of the land are covered with open savanna grassland. The dominant tree species are Acacia seyal, Acacia sieberiana, and Acacia tortilis. The grasses most encountered in the area are Hyperanium spp. and Sorghum spp. There are 876 zebu cattle, 606 sheep and 337 goats. The human population in the area is 641 (283 male and 358 female). The main activity of the local people is farming. Three species of tsetse were encountered in the study area G. m. submorsitans, G. pallidipes and G. f. fuscipes.
101
Fig. 1. Location map (modified Leak et al., 1993) of the study site in the Ghibe River Valley, Ethiopia.
Sampling of the target tsetse flies was made from October 2000 up to September 2001. Sampling was taken for five consecutive days in each month. Six odour baited monoconical traps (Laveissiere and Grebaut, 1990) were used to sample flies. The distance between each trap was 200 m. The bait was acetone plus cow urine, with the release rate of 500–600 mg/h for acetone and 1–1.2 g/h for cow urine (Vale et al., 1988). Sampling was made from all possible tsetse habitats including habitats along the Ghibe River and in open savanna 10 kms apart from the river. Each sampling point was marked with dyed wooden poles for consecutive sampling. The apparent density, which often expressed as the number of tsetse caught per trap per day (flies/(trap day)) of G. m. submorsitans was estimated using a method described by Rogers (1983). Tsetse population density is less variable than those of many other insects. Thus field estimates of apparent density can be used for estimating disease risk. Infection rate in tsetse flies was determined through dissection (Lloyd and Johnson, 1924). This method involves the examination of salivary glands, proboscis and mid gut for infection by trypanosomes. Accordingly, when trypanosome infection was found only in the proboscis, it was considered to be Duttonella, whereas when found both in the proboscis and mid gut, it was
102
Merid Negash et al. / Acta Tropica 102 (2007) 100–105
considered to be Nanomonas and similarly when found in salivary gland it was considered to be Trypanozoon (Lloyd and Johnson, 1924). From trapped flies, those fed once were selected for blood meal identification. The abdomen was cut off using a clean scalpel and clean forceps. The blood filled gut was pulled out of the abdomen on to the Whatman No. 1 filter paper which was labeled into eight sections using pencil. The blood was then smeared on to the filter paper; air dried and kept in a desiccator. The blood specimens were sent to ICIPE Nairobi, Kenya for analysis using enzyme linked immunosorbent assay (ELISA) (Service et al., 1986). The range of conjugates tested included: baboon, bovidae, bush buck, bush pig, cattle, camel, chicken, crocodile, dog, goat, grants gazelle, hippopotamus, human, kudu, lion, ostrich, rhino, sheep, Thomson’s gazelle, warthog, water buck. 3. Statistical analysis The monthly variation in tsetse density was analyzed using Kruskal–Wallis H analysis of variance, followed by Mann–Whitney U test. Infection rate between male and female as well as between the different parasites were subjected to Chi-square test. The statistical package used was SPSS Version 10.00 for windows (SPSS Inc., 1999). 4. Results G. m. submorsitans occurred with a mean apparent density of 4.26 ± 0.49 flies/trap/day. The apparent density result elucidates a significant variation between months (P < 0.0001) (Fig. 2). Apparent density decreased during the dry months except on January and increased from May (start of rain) until it attained its peak in October (beginning of the dry months) after which it again decreased sharply in November. From 450 G. m. submorsitans examined for infection rate determination, 4.7% of the flies harbored trypanosome (Table 1). Of the infected flies, 76% were
Fig. 2. Monthly mean trap catch of Glossina morsitans submorsitans in Ghibe River Valley, Southwest Ethiopia (2000–2001). The same letters within each series indicate values that are not different according to nonparametric Kruskal–Wallis analyses of variance followed by a paired Mann–Whitney U test.
female while 24% were male. The difference was found to be significant (χ2 , 5.762 P = 0.016). The trypanosomes encountered belong to Nanomonas, Duttonella and Trypanozoon subgenus and occurred in the proportions of 54.14%, 38.1% and 4.76%, respectively. More flies were infected with Nanomonas than Trypanozoon. Similarly more flies were infected by Duttonella than Trypanozoon. The variation was statistically significant χ2 , 9.308, d.f. = 1, P = 0.002 and χ2 , 5.444, d.f. = 1, P = 0.02, respectively. However, no significant difference was observed between Nanomonas and Duttonella (χ2 , 0.8, d.f = 1, P = 0.371). From a total of 139 blood samples collected, 76 (54.68%) samples were confirmed to be host blood. Among these hosts, 36.84% of meals were obtained from cattle, 25% from Kudu. Suidae (warthog and/or wild pig) made about 11.84% of the meals, human beings made about 10.53%, goat about 6.58%, bovidae about 5.26% (which refers to any wild ruminant in the bovidae family excluding those listed among the conjugates), 2.63% of the meals was taken from baboon and 1.32% was taken
Table 1 Infection rate in male and female G. m. submorsitans and percentage composition of trypanosome subgenus identified in Ghibe River Valley, Southwest Ethiopia (2000–2001) Trypanosome subgenus
Male (194)
Female (256)
Total
Percentage of trypanosome subgenus
Nanomonas Duttonella Trypanozoon Total trypanosomes infected Trypanosome infection rate (%)
3 2 0 5 2.6
9 6 1 16 6.25
12 8 1 21 4.7
57.1 38.1 4.8
Number in parenthesis is total tsetse flies checked for infection.
Merid Negash et al. / Acta Tropica 102 (2007) 100–105
Fig. 3. Host preference of G. m. submorsitans in Ghibe River Valley, Southwest Ethiopia (2000–2001).
from water buck/Reedbuck (Fig. 3). Sixteen (21.05%) of the blood meal samples collected were unidentified, i.e. were not within the host range available. 5. Discussion The observed pattern of fluctuation in apparent density (Fig. 2) showed that G. m. submorsitans was most abundant during the rainy months. This result is in agreement with previous works on seasonality of G. m. submorsitans in other parts of Africa (Snow, 1981; Getachew, 1983). However, environmental, as well as biological factors, may attribute for high number flies caught in January. There was a shower of rain in January, which might have reduced adult mortality in that month (Merid et al., 2004). The infection rate of G. m. submorsitans was found to be low for morsitans when compared to 15–20% infection rate obtained by other researchers (Glasgow, 1963; Ford, 1971; FAO, 1982). Since the dissection methods lacks sensitivity and unable to detect mixed infection as opposed to more sensitive methods such as PCR and dotELISA (Morlais et al., 1998; Ouma et al., 2000; Solano et al., 2001) that could be main reason for low infection rate. The present results are different from previous findings by Getachew (1983) and Habtamu (1993), who had done similar work on the same species at Fincha and Didessa valleys (western Ethiopia) and who obtained 0.5% and 2.65% infection rate, respectively. This may be due to the difference in feeding habit of G. m. submorsitans in the two areas, because, according to Jordan (1965), tsetse flies feeding on domestic or wild bovidae are more likely to be infected than those feeding on suids.
103
From the present study, a greater number of G. m. submorsitans was infected with Nanomonas. According to Ford (1971) in East Africa, it is generally found that when morsitans are vectors of Trypanosoma vivax and Trypanosoma congolense, the later is usually the dominant trypanosome. Since G. m. submorsitans and G. pallidipes are found in the area this may be one of the reasons for the Nanomonas predominance. T. congolense is the predominant trypanosome in cattle populations within or close to the infestation of Glossina (Jordan, 1986). As the distance from known tsetse infestation increase Trypanosoma vivax becomes more frequent and eventually predominant in cattle. Since this study was done in the main infestation area this may be one of the reasons for the higher percentage of Nanomonas. Similarly, according to Moloo et al. (2000) who demonstrated that tsetse flies feed more successfully on cattle infected with T. congolense than on cattle infected with T. vivax this could also contribute for Nanomonas dominance. Farmers in the study area extensively use trypanocidal drugs to treat their cattle. T. congolense was found to be more resistant to the available drugs, diminazene aceturate, isometamidium chloride and homidium chloride in the area (Codjia et al., 1993). The drugs used may have greatly reduced the incidence of susceptible Duttonella, enabling resistant Nanomonas to become predominant. Female G. m. submorsitans were found to be more infected than males (Table 1), which agrees with previous works (Glasgow, 1963). Although it is difficult to generalize, this may be because females live longer and feed more frequently than males, thus having greater chances to feed on infected hosts. The three detected parasites in G. m. submorsitans make it epizootiologically very important, since Nanomonas and Duttonella cause very serious disease in cattle. Trypanozoon causes very serious disease in horses and donkeys, which may be the main reason for the exclusion of donkeys and horses in the area (even though it needs further investigation), which seriously affects the livelihood and activity of the people living in the area, since these animals are very important for transportation and traction. In the area, there is movement of cattle to reach new grazing ground (especially during the dry season) and markets. This movement can aggravate the spread of trypanosomosis both within the infected area and into areas known to be outside the tsetse belt. In the latter case, it is mainly due to mechanical transmission. The distribution and abundance, of Glossina spp. is closely associated with the presence and distribution of their hosts. It was difficult to collect enough engorged flies as stationary traps catch hungry flies, which seek
104
Merid Negash et al. / Acta Tropica 102 (2007) 100–105
host to feed. But it was possible to collect 139 blood meal samples. From the present investigation, cattle were found to be the most preferred host followed by kudu (Fig. 3). In areas where cattle are restricted, like in dense forests, G. m. submorsitans feed more on warthog. According to Snow and Borham (1979); who carried out their study in the West Kiang of Gambia where cattle are very restricted in their contact with woodland areas (a preferred habitat of G. m. submorsitans) 90% blood source of G. m. submorsitans was obtained from warthog. According to Clausen et al. (1998) 57.1% of meal of G. m. submorsitans was derived from Suidae in which warthog accounts 37%. Warthog is one of the reliable hosts of tsetse (Nash, 1969) having a relatively restricted home range in favoured tsetse habitats and being most active in the early morning and late afternoon when tsetse are active too (Torr, 1994). Similarly, Habtamu (1993) reported that 52.9% of G. m. submorsitans meal was from warthog. Moloo (1993) has summarized the hosts of the different tsetse species and the order of host preference for G. m. submorsitans goes as warthog, human, and cattle, respectively. In East Africa, where bovids are abundant, G. m. submorsitans feed less on warthog than in areas where wild bovidae are relatively scarce (Jordan et al., 1962). Moreover, the epidemiology of vector borne diseases is complex and related to the ecology of host, vectors and parasites (de La Rocque et al., 2005). The present result agrees with this explanation where cattle followed by kudu were the preferred host of G. m. submorsitans. Therefore, kudu might be the main wild animal host that supports the tsetse population in the area and the reservoir of the three pathogens detected in G. m. submorsitans. However, the role of other wild hosts should not be undermined especially the suids as they are highly infected by trypanosomes (Hoare, 1972). Human beings were also found to be host of G. m. submorsitans in the area. The activities of the people are predominantly production of charcoal as fuel source, and collecting honey as a means of complimentary income. There is also a footpath through which people from other areas cross this tsetse belt to reach the market place. These activities might have created a close contact between tsetse and human beings. Therefore, G. m. submorsitans could also be epidemiologically important by transmitting the zoonotic (Rhodesian) human trypanosomosis if infected animal, human or reservoir game animals are introduced in to the region accidentally. The blood meals (21.05%) which were out of detection range may be taken from hosts that were not included in the conjugate for the blood meal analysis.
Acknowledgements The work was sponsored by the African Regional Postgraduate Program in Insect Sciences (ARPPIS), we also thank Addis Ababa University Department of Biology and ICIPE, Ethiopia (especially Dr. Getachew Tikubet), for logistic and technical support. Vestergaard Frandsen Group is acknowledged for providing experimental traps. ILRI’s Ghibe research station is equally appreciated allowing us to use their laboratory facilities. Comments given by the three anonymous reviewers were both useful and encouraging for which we are grateful.
References Clausen, P.H., Adeyemi, I., Bauer, B., Breloeer, M., Salchow, F., Staak, C., 1998. Host preferences of tsetse based on blood meal identifications. Med. Vet. Entomol. 12, 169–180. Codjia, V., Woudyalew, M., Majiwa, P.A.O., Leak, S.G.A., Rowlands, G.J., Authie, E., d’Iteren, G.D.M., Peregrine, A.S., 1993. Occurrence of populations of Trypanosoma congolense resistant to diminazene, isometamidium and homidium in the Ghibe Valley, Southwest Ethiopia. Acta Trop. 53, 151–163. de La Rocque, S., Michel, J.F., Bouyer, J., De Wispelaere, G., Cuisance, D., 2005. Geographical information systems in parasitology: a review of potential applications using the example of animal trypanosomosis in West Africa. Parasitology 47, 97–104. FAO, 1982. In: Pollock, J.N. (Ed.), Tsetse Control Training Manual, vol. 1. Tsetse Biology, Systematic and Distribution, Techniques. Food and Agriculture Organization of the United Nations, Rome, p. 280. Ford, J., 1971. The Role of Trypanosomiasis in African Ecology. A Study of Tsetse Fly Problem. Clarendon press, Oxford, p. 568. Ford, J., Makin, M.J., Grimble, R.J., 1976. Trypanosomiasis Control Programme for Ethiopia. Report to the Ethiopian Government of the British Technical Assistance Team appointed to determine a programme for tsetse fly and trypanosomiasis control and subsequent land use in south-western Ethiopia. Ministry of Overseas Development of Great Britain, p. 127. Fuller, G.K., 1978. Distribution of Glossina in South Western Ethiopia. Bull. Ent. Res. 68, 299–302. Getachew, T., 1983. Studies on tsetse flies of Finchaa River Valley. MSc Thesis. A.A. University School of Graduate Studies, 83 pp. Glasgow, J.P., 1963. The Distribution and Abundance of Tsetse. Pergmon Press, Oxford, p. 241. Habtamu, B., 1993. Host, trap and odour bait preference determination of tsetse flies (G. m. submorsitans) in the upper Didessa Valley Southwest Ethiopia. MSc Thesis. A.A. University School of graduate Studies, 65 pp. Hoare, C.A., 1972. The Trypanosomes of Mammals. Blackwell Scientific Publications, Oxford, p. 749. Hutchinson, M.P., 1971. Human trypanosomiasis in Southwest Ethiopia. Ethiopia Med. J. 9, 3–69. IAEA, 1996. Government of Federal Democratic Republic of Ethiopia Draft Projects Document Integrating the Sterile Insect Technique to Eradicate tsetse from the Southern rift Valley of Ethiopia. December.
Merid Negash et al. / Acta Tropica 102 (2007) 100–105 International Scientific Council for Trypanosomosis Research and control (ISCTRC), 1999. Proceedings of the ISCTRC 24th Meeting. pp. 77–81. OAU/STRC Publication, Maputo, no. 119. Jordan, A.M., 1965. Long-term fluctuations in numbers of a population of Glossina sixteen years observations. In: Proceedings of the 10th Meeting. International Scientific Committee for Trypanosomiasis Research. Kampala, 24–28 October, 1964, pp 85–90. Commission for Technical Co-operation in Africa, Lagos (Publication no.97). Jordan, A.M., 1986. Trypanosomiasis Control and African Rural Development. Longman, London, p. 357. Jordan, A.M., Jones, F.L., Weitz, B., 1962. The natural hosts of tsetse flies in northern Nigeria. Ann. Trop. Med. Parasitol. 56, 430–442. Laveissiere, C., Grebaut, P., 1990. recherches sur les pieges a Glossines (Diptera: Glossinidae) mise au point d’un mode’le economique le piege ‘Vavoua’. Trop. Med. Parasitol. 41, 185–192. Leak, S.G.A., Woudyalew, M., 1993. Advance of Glossina morsitans submorsitans and Glossina pallidipes along the Ghibe river system in southwest Ethiopia. Acta Trop. 55, 91–95. Leak, S.G.A., Woudyalew, M., Authie, E.d’Ieteren, Peregrine, A.S., Rowlands, G.J., Trail, J.C.M., 1993. Epidemiology of bovine trypanosomiasis in the Ghibe Valley, southwest Ethiopia. Tsetse challenge and its relationship to trypanosome prevalence in cattle. Acta Trop. 53, 121–134. Lloyd, L., Johnson, W.B., 1924. The trypanosome infections of tsetse flies in northern Nigeria and a new method of estimation. Bull. Ent. Res. 14, 265–288. Merid, N., Melaku, G., Emiru, S., 2004. Seasonality and diel activity pattern of Glossina morsitans submorsitans in Ghibe River Valley. SINET: Ethiop. J. Sci. 27 (2), 135–142. Moloo, S.K., 1993. The distribution of Glossina species in Africa and their natural hosts. Insect Sci. Appl. 4, 511–527. Moloo, S.K., Sabwa, C.L., Baylis, M., 2000. Feeding behaviour of Glossina pallidipes and G. morsitans centralis on Boran cattle infected with Trypanosoma congolense or T.vivax under laboratory conditions. Med. Vet. Entomol. 14, 290–299. Morlais, I., Grebaut, P., Bodo, J.M., Djoha, S., Cuny, G., Herder, S., 1998. Detection and identification of trypanosomes by polymerase chain reaction in wild tsetse flies in Cameroon. Acta Trop. 70, 109–117. Nash, T.A.M., 1969. The tsetse fly. In: African Bane. Collins Clear Tepe Press, London, p. 215.
105
Ouma, J.O., Masake, R.A., Masiga, D.K., 2000. Comparative sensitivity of dot-ELISA. PCR and dissection method for the detection of trypanosome infections in tsetse flies (Diptera: Glossinidae). Acta Trop. 75, 315–321. Ovazza, M., 1956. Contribution a 1’eiude des dipteres vulnerants de 1’empire d’Ethiopie IV. Glossina. Bull. Soc. Path. Exot. 49, 204–209. Reid, R.S., Kruska, R.L., Muthui, N., Wotton, S., Wilson, C.J., Andualem, T., Woudyalew, M., 1997. Distinguishing the impacts of change in trypanosomiasis severity from other factors that cause land use change over time in southwestern Ethiopia. In: Proceedings of the 24th Meeting of the International Scientific Council for Trypanosomosis Research and Control, Maputo, Mozambique. Rogers, D.J., 1983. Trypanosomiasis ‘Risk or challenge’: a review with recommendations livestock productivity and trypanotolerance. In: Network Training Manual. ILCA Addis Ababa, Ethiopia, pp. 101–127. Service, M.W., Voller, A., Bidwell, D.E., 1986. The enzyme-linked immunosorbent assay (ELISA) test for the identification of bloodmeals of haematophagous insects. Bull. Ent. Res. 76, 321– 330. Snow, W.F., 1981. Tsetse ecology and epidemiology of trypanosomiasis in the Gambia and on the south Kenya coast: a comparison. In: Proceedings of the 16th Meeting International Scientific Council for Trypanosomiasis Research. Yaound´e, 1979, pp. 369–381. Organization of African Unity, Scientific and Technical Research Commission (Publication no. 111). Snow, R.K., Borham, P.F.L., 1979. The feeding and ecology of tsetse fly Glossina m. submorsitans in relation to nagana transmission in Gambia. Acta Trop. 36, 47–51. Solano, P., Guegan, J.F., Reifenberg, J.M., Thomas, F., 2001. Trying to predict and explain the presence of African trypanosomes in tsetse flies. J. Parasitol. 87, 1058–1063. SPSS Inc., 1999. SPSS for Windows Version 10.00. SPSS Inc., Chicago. Torr, S.J., 1994. Responses of tsetse flies (Diptera: Glossinidae) to warthog (Phacochoerus aethiopicus Pallas). Bull. Ent. Res. 66, 713–729. Vale, G.A., Hall, D.R., Gough, T.A.E., 1988. The olfactory response of tsetse flies. Glossina spp. (Diptera: Glossinidae) to phenols and urine in the field. Bull. Ent. Res. 78, 293–300.