A seroepidemiological study of African horse sickness in Limuru and Lari districts, Kenya

Status
Status: 
Completed
Applicants
Collaborators
Researchers
Award types
Donkey Sanctuary awards: 
MSc
Details
When conducted: 
1 April 2010 - 31 July 2011
Country: 
Kenya
Core methodology: 
Prospective questionnaire, clinical examination.
Aims: 
1) To estimate the prevalence of AHS antibodies in the donkey population of Kiambu West District, Kenya. 2) To identify the risk factors for AHS in this population. 3) To determine the level of knowledge on AHS in donkeys among donkey owners in Kiambu West District, Kenya.
Results: 
1) The sero-prevalence of AHS in donkeys sampled after the heavy rains was estimated at 35.2% (70/199) for the two divisions, while that for the dry season was estimated at 26.7% (55/199). The prevalence of AHS in donkeys during the two periods was 31% (125/398). There was a statistically significant difference in the two prevalences (Z=2.89). The prevalence of AHS in the donkeys that were re-sampled in Kambaa, decreased from 60% (18/30) in May/June to 20% (6/30) in August/September. This difference (Z=4.47) indicates that donkeys are not long term carriers of AHSV or fewer vectors during the dry season. There was a poor level of agreement between ELISA test results and clinical presentation of the illness as only 3 cases were presented with clinical signs of a swollen head and congested conjunctival mucosa. These 3 cases had detectable antibodies to the virus, the poor agreement was with the other 67 cases positive on ELISA test but with absence of clinical signs. Further studies need to be carried out to determine the duration that AHSV antibodies remain present in donkeys. 2) Division and sub-location were controlled in the mixed models logistic regression analysis of the risk factors. In the univariate analysis, age of the donkeys, presence of a water stream, source of the donkey, donkey use, vaccination status and housing were the statistically significant variables and were thus included in the multivariate analysis. Age of the donkey (p-value 0.02) and presence of a water stream (p-value 0.03) were significant risk factors and might have contributed to the high prevalence of AHS among donkeys in Kambaa and Rwamburi sublocations. This meant that older donkeys (9-12yrs) and those grazing near water streams were two times more likely to be exposed to AHSV. A water stream likely favoured increased vector(s) population, and transmission of the AHSV. 3) A small proportion, 21.9% of questionnaire respondents knew of AHS. 8.2% were familiar with the clinical signs of swollen head and congested conjunctival mucosa and 9.5% reported severe body weakness as a sign of the disease. The low level of awareness of AHS among household members may be attributed to lack of previous dissemination of information on the disease. Many respondents reported donkeys with AHS clinical signs as having been poisoned, bitten by snakes or suffering from sudden pneumonia – in hindsight these donkeys may have been AHS cases. Low public awareness of the disease may be resulting in under-reporting.
Conclusions: 

1) African Horse Sickness is endemic in donkeys in all six of the study sub-locations of Lari and Limuru divisions.
2) The prevalence of AHS in donkeys demonstrates a seasonal variability; which was 35.2% in the rainy season and 27.6% in the dry season.
3) Clinical signs may be used as a diagnostic indicator for the presence of AHS in donkeys. However, sub-clinical cases may be appropriately diagnosed using ELISA.
4) AHS presents a clinical form of disease in donkeys that has a seasonal manifestation.
5) Age (9-12) and presence of water streams near grazing areas are significant risk factors.
6) Vaccination against AHS was not practiced in this region; hence seropositivity was not confused in terms of interpretation of data.