Epidemiological Investigation of Mechanically Transmitted Trypanosomosis (Trypanosoma Vivax) Of Domestic Animals in Three Districts Bordering Lake Tana, Ethiopia
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2004-06
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Abstract
An epidemiological investigation of mechanically transmitted trypanosomosis was undertaken at the three districts (Bahir Dar Zuria, Dembia and Fogera) bordering lake Tana that are located in Amhara National Regional State, Ethiopia. The study was conducted with the objectives of determining the prevalence of trypanosomosis in cattle, small ruminants and equines, identifying biting flies and investigating the presence of drug resistance to Isomethamidium chloride and Diminazine aceturate in the study areas.
The methodology followed was that a total of 1509 cattle, 798 small ruminants and 749 equines were considered for the prevalence study using parasitological methods (buffy-coat method) and the PCV of each animal was measured using hematocrit techniques. A total of 86 traps (66 NGU and 20 Monoconical) were deployed for the purpose of fly survey. At the Fogera district 48 cattle (in the late rainy season) and 19 cattle (in the early dry season) positive for Trypanosoma vivax after treatment with Isomethamidium chloride and Diminazine aceturate respectively were followed for 3 months and 24 days, respectively.
The results indicated that the overall prevalence of trypanosomosis in cattle was 6.1% (92/1509). Prevalence was significantly (t =-3.5, P<0.001.) higher during the late rainy season 9.6% (57/592) than the early dry season 3.6%(22/609) at Fogera district where the two seasons were compared. Prevalence at the district level has significantly varied (p<0.01) from 9.6% (57/592) at Fogera district to 4.5%(6/133) at Bahir Dar and 4% (7/175) at Dembia. Prevalence at a peasant association level has significantly (p<0.01) varied from 0% (0/54) (Sebatamit, Bahir Dar) to 15.5% (37/239) (Shina, Fogera). Among small ruminants only one sheep 0.8% (1/122) and one goat 0.15% (1/676) were found positive for Trypanosoma species and none of the equines were positive. All the trypanosomes encountered in cattle belong to a single species of T. vivax. However the Trypanosoma species in sheep and goats though it seemed T. vivax from the movements of buffy-coat smear, it was not possible to get with in the thin smear preparation made from the buffy-coat which may be due to the very low number of parasites in the blood (single parasites per preparation for each species at the buffy coat). The PCV for each species of animal was with in the normal range available in literature. The PCV of T. vivax infected cattle (PCV=21.6, 95%CI=20.9-22.3) was significantly (p<0.001) lower than the negatives (PCV=25.4, 95%CI=25.2-25.5) and PCV values were also significantly and positively associated with body condition score (p<0.001), and pregnancy (p<0.01), and negatively associated with lactation (p<0.05) and parity (p<0.01) in cattle. There was also a significant variation in PCV among the three districts (p<0.01) and between the two seasons (p<0.01) in cattle.
A total of 71,273 flies were caught of which 49,353(69.2%) belong to Stomoxys, 15,875(22.3%) to non-biting Muscidae, 4,715(6.6%) to horse flies and 1,330(1.9%) to Chrysops and there was no tsetse fly. The overall apparent density was 276.3 flies/trap/day. The NGU trap had a significantly (P<0.05) high catch of horse flies than the Monoconical where as the Monoconical trap had a significantly high catch of Stomoxys (p<0.0001) over the NGU trap. However, there was no significant difference in catchments between the two traps for non-biting Muscidae (NBM) and Chrysops species. Seasonal comparison at Fogera district has revealed that there was a statistically significant variation (p<0.001)) of high fly catchments in the late rainy season than the early dry season for each type of traps alone and together for Stomoxys, horse flies and Chrysops species. However, there was no significant seasonal variation for the non-biting Muscidae. Fly species identified include Atylotus agrestis, Chrysops streptobalia, Stomoxys calcitrans, Stomoxys nigra, S. pulla, S. pallida, S. sataiens, S. taieniata and Hippobosca variegata. A single specimen of the genus Tabanus and Hematopota were also encountered.
Of cattle subjected to both Isomethamidium chloride and Diminazine aceturate drug sensitivity trial, none of the animals were positive for trypanosoma during the follow up period and at the end of the trail mean PCV has significantly improved by 3.6% for Isomethamidium chloride (t= -8.48, P<0.0001) treated group (22.7, 95% CI=21.8-23.61 at day zero and 26.3, 95% CI=25.4-27.3 at day 90 post treatment) and 2.6% for Diminazine aceturate (t = -4.9, P < 0.001) treated group (20.1, 95% CI=19.0-21.2, at day zero and 22.7, 95% CI=21.6-23.7 at day 24 post treatment) respectively.
In general, the present study has indicated that trypanosomosis due to T. vivax is relatively important in cattle, and small ruminants would get the infection. Infection with T .vivax has negatively affected the PCV of cattle. Various biting flies of veterinary-medical importance are present and tsetse flies were not encountered during the study period. This indicates that T .vivax infection in the study area is transmitted mechanically mediated by biting flies. T. vivax infection in cattle of the study districts is sensitive to both Isomethamidium chloride (at 1 mg/kg BW dose rate) and Diminazine aceturate (3.5 mg/kg BW) as a prophylactic and normal curative doses respectively. Therefore, a particular attention towards T. vivax infection in cattle is essential to control the impact of the disease on productivity. Development of control options that could minimize biting flies especially in seasons of high vector population is another task. Treatment of T. vivax positive cattle with Diminazine aceturate would be effective and economical till problems of drug resistance might arise due to Diminazine aceturate. Finally, further studies on biting flies (species behaviors, breeding habitat, host preference, control alternatives, relative importance with regard to T. vivax transmission and other relevant aspects) are recommended.
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Trypanosoma vivax, diminazine, cattle, , small ruminants