SERO-EPIDEMIOLOGY OF SELECTED ARBOVIRUSES AMONG FEBRILE PATIENTS IN THE LAKE/RIVER BASINS OF LAKE BARINGO, LAKE NAIVASHA AND RIVER TANA, KENYA

Abstract

Arboviruses cause emerging and re-emerging infections affecting humans and animals. They are spread primarily by blood-sucking insects such as mosquitoes, ticks, midges and sand flies. Changes in climate, ecology, demographics, land-use patterns and increasing global travel have been linked to an upsurge in arboviral disease. Outbreaks occur periodically followed by persistent low level circulation. This study aimed at determining the seroepidemiology of selected arboviruses among febrile patients in selected lake/river basins of Kenya. Using a hospital-based cross-sectional descriptive study design, febrile patients were recruited into the study retrospectively using simple random sampling from an ongoing study and actively from three health facilities namely; Marigat, Mai Mahiu and Kotile. Out of the 379 patients enrolled, 285 were retrospective samples and 94 were collected actively. A structured questionnaire was administered to collect socio-demographic and clinical data. The patient‘s venous blood was tested for IgM and IgG antibodies to determine exposure to selected arboviruses including Crimean Congo Haemorrhagic fever virus (CCHFV), Rift Valley fever virus (RVFV), West Nile virus (WNV), and Alphaviuses. Samples positive for Alphaviuses and WNV were further subjected to plaque reduction neutralisation test (PRNT) to confirm the presence of the specific antibodies. PRNT was not performed for CCHFV and RVFV because they are highly pathogenic viruses that require high containment to manipulate in the laboratory which is not available in Kenya. Multiple logistic regression models were used to assess the risk factors associated with the exposure of humans to CCHFV, RVFV, WNV and Alphaviuses. Important socio-demographic and clinical characteristics associated with arboviral infections like age, site, contact and fever were identified. Of the 379 samples examined, only on sample was positive for Anti-CHIKV IgM antibodies and 46.4% (n=176, 95% CI: 41.4-51.5%) were IgG positive for at least one of these arboviruses. Virus specific prevalence for CCHFV, RVFV, WNV and Alphaviuses was 25.6%, 19.5%, 12.4% and 2.6%, respectively. These prevalences varied significantly (p<0.001) with geographical site, where Tana recorded the highest overall arboviral seropositivity of 60%, followed by Baringo (52%) and Naivasha (32%). PRNT results for Alphaviruses confirmed that the actual virus circulating in Baringo was Semliki Forest virus (SFV), in Naivasha was CHIKV, O‘nyong nyong virus (ONNV), and SFV, and in Tana delta Sindbis virus (SINDV). Among the Flaviviruses tested, WNV was circulating in all the three sites. This study also determined that age, site, gender and contact with goats were risk factors for arboviral infections. The findings of this study suggest a high burden of febrile illness in humans due to CCHFV, RVFV, WNV and Alphaviuses infection in the river/lake basin regions of Kenya, which should be brought to the attention of public health authorities in these areas.