Epidemiology and control of donkey trypanosomiasis and their vectors in the Lamu Islands

Award types
Other awards: 
Clinical research
When conducted: 
1 December 2008 - 1 April 2010
The Trypanosomiasis Research Centre, Nairobi, Kenya
Core methodology: 
2 study periods (dry and wet season), PRA, tsetse fly survey, tick survey, buffy coat technique (BCT), Giemsa staining, faecal egg count (FEC), drug sensitivity testing, social survey.
1) To conduct participatory rural appraisal (PRA) of donkey farmers and community health workers with a view to assess their knowledge of donkey health and husbandry issues and therefore determine possible community intervention points. 2) To determine the association between host, temporal, spatial and management factors and prevalence of trypanosomiasis and babesiosis in the donkey population of the Lamu archipelago. 3) To characterise the isolated trypanosomes through phenotypic, molecular and drug sensitivity determinations. 4) To determine the seasonal distribution and vectorial capacity of tsetse (and non-tsetse) vectors of trypanosomiasis in the archipelago.
1) Amongst the greatest constraints of donkey keeping were diseases including trypanosomiasis. As far as trypanosomiasis is concerned, findings indicate that the inhabitants of the Island were knowledgeable about the link between trypanosomiasis and tsetse. Apart from tsetse, the other vectors that affected donkeys included ticks, mites and biting flies. However, the distinction between tsetse flies and various biting flies was difficult for the respondents to make. The presence of wounds in donkeys and indications from key informants about overloading, over beating and poor watering practices as constraints may be a pointer to the need for increased sensitization of keepers for improved donkey management practices and increased productivity. The management of donkey health problems was perceived as a role to be played by the Donkey Sanctuary personnel. Community ownership of donkey management in terms of diseases and deworming was low. The majority of FEC results (McMasters) were negative, 84 and 72.3% in the dry and wet seasons respectively. Scarcity of feed and pasture for donkeys was also singled out as a constraint. 2) Trypanosomes were encountered in 3.1 and 7.5% of donkeys examined in dry and wet season respectively, the association between prevalence and season was significant at p<0.05. There was no significant difference in prevalence rates between villages. Infection rates were higher in donkeys in poor body condition ranging from 12 to 46% percent of poor donkeys in the dry and wet season respectively as opposed to 1.9 and 6.1% of those in good body condition. During both seasons mean PCVs of infected, young, female and donkeys in poor condition were lower than that of uninfected, adult, male and good condition donkeys. Anaemia (PCV <25%) was present in 88 and 71% of infected donkeys compared to 34.1 and 37.7% of uninfected donkeys in the dry and wet seasons respectively. Full results of PCR analysis are not available but preliminary indications are that there may be a number of sub-patent infections accounting for the anaemia. 3) Three species of trypanosomes were detected via BCT and Giemsa staining: Trypanosoma congolese Broden (68.7% of cases), Trypanosoma vivax Zieman (21.8%), Trypanosoma brucei Plimmer and Bradford (6.2%) and 6.2% of donkeys had mixed infections. BCT technique has limitations in cases of chronic infection and PCR analysis for a more accurate identification of prevalence is still pending, initial results indicate further species of Trypanosomes may be present and confirm suspicions of false negative results using smears. Drug sensitivity evaluation was hampered by difficulties with in vitro cultivation and was ceased. Ticks were identified in 51 and 43% of donkeys in dry and wet seasons respectively, although mean number of ticks were very few at 4.2 and 2.6 for dry and wet seasons. Dry season donkeys were found to be free from tick-borne disease, however Babesia was identified in 6 donkeys sampled in the wet season. Prevalence of ticks varied between villages in the wet season (p=0.0002), results showed that donkeys regularly driven through seawater would have fewer ticks. 4) The entomological surveys revealed the presence of Glossina pallidipes Austen species of tsetse fly and other biting flies Stomoxys spp. Linnaeus, Tabanus spp. Linnaeus and Haematopota spp. Linnaeus were also caught. Tsetse fly dissection did not reveal any trypanosomes, however PCR sample results may be a truer measure of trypanosome challenge as dissection may underestimate true infection rates.

This study confirmed the importance of trypanosomiasis in donkey health and productivity and negates the common notion that donkeys are disease-resistant. Veterinary and extension workers should give donkeys equal attention as other domestic livestock, considering the important role they play in domestic economies. Trypanosomiasis is a major cause of anaemia and unthriftiness in donkeys, results associate anaemia as a reliable sign of either overt or subpatent trypanosomiasis and donkeys with pale mucous membranes should be considered for treatment for trypanosomiasis.
The distribution and numbers of tsetse do not justify vector control interventions. Donkeys originating from the mainland should be treated prior to shipment due to high prevalence rates, limited sensitivity testing of isolates identified no reason to review the dosage of samorin currently in use (0.5mg/kg). Tick numbers were low but simple control strategies such as bathing in salt water appear to be effective so should still be emphasized.