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Epidemiological studies on camel trypanosomosis (surra) and its control and economic impact in Somaliland

Salah, A.A. (2016) Epidemiological studies on camel trypanosomosis (surra) and its control and economic impact in Somaliland. PhD thesis, Murdoch University.

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Abstract

Surra is a disease caused by the pathogenic trypanosome, Trypanosoma evansi, and is distributed throughout Africa, Asia and South America. The study outlined in this thesis was conducted to determine the epidemiology of trypanosomosis in camels, its economic impact on camels raised under a traditional pastoral production system and potential vectors that could transmit the disease between camels in Somaliland. Prior to this study there was limited information on the distribution and impact of surra in camels in Somaliland, although field reports indicated significant losses of production and consequently impact on the livelihood of pastoralists.

In this study 2,575 camels were sampled from 144 herds and tested with the CATT/T. evansi. The animal level test seroprevalence observed was 26.4% (95% CI 24.8, 28.2) (real prevalence after adjusting for test sensitivity and specificity was 38.2%; 95% CI: 36.0, 40.0). The seroprevalence varied significantly between regions (p < 0.05) with a higher level (37.2%) in Sahil than in Awdal (19.3%) or Waqoyi Galbed (17.4%).

A susceptible-infectious-subclinical (SIC) model was constructed in order to determine criteria for successful disease control by mass and targeted chemotherapy. This was used to simulate and estimate the economic benefits of four different control options against surra in camels. Adopting biannual treatment of all camels, monthly targeted treatment of clinically sick camels or biannual targeted treatment of seropositive camels was estimated to result in a benefit of US$141,431, 170,577 and 114,625 per village (80 camels) for a five year period in the study area, respectively.

The prevalence after five years of control was predicted to be 7.4, 6.4 and 6.7% for the biannual treatment of all camels, monthly targeted treatment of clinically sick camels or biannual targeted treatment of seropositive camels, respectively compared with 72.2% if no treatments were applied. The annual revenue lost in the studied camel herds was estimated at US$404,630 (20159 camels studied) if no treatment was administered. The greatest loss was associated with decreased milk yield (US$314,630).

As part of this research Nzi and biconical traps were set to trap tabanids responsible for transmitting trypanosomosis. Three genera of tabanids were trapped (Philoliche, Tabanus and Haematopota) and these flies were recognised as potential vectors of trypanosomosis in camels. Philoliche species were the most widely distributed and abundant biting flies in the area. The activity of the biting flies differed throughout the day, with the highest activity observed in the middle of the day and the lowest in the afternoon. There was a significant difference between the alighting sites of biting flies on camels, with the lower body and belly of camels being the preferred sites compared to the upper body (head, neck and hump). In this study on average 0.87 ± 0.34 flies of the Philoliche genus alighted on the lower body and belly of camels in the middle of the day.

The results of this study strongly support the need for implementation of surveillance and control programs for trypanosomosis in camel herds in Somaliland.

Publication Type: Thesis (PhD)
Murdoch Affiliation: School of Veterinary and Life Sciences
Supervisor: Robertson, Ian
URI: http://researchrepository.murdoch.edu.au/id/eprint/36203
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