Exposure patterns and the risk factors of zoonotic Crimean Congo hemorrhagic fever virus amongst pastoralists, livestock and selected wild animals species at the human/livestock/wildlife interface in Isiolo County, upper eastern Kenya

Abstract

Crimean Congo hemorrhagic fever (CCHF) is a tick-borne zoonotic disease caused by CCHF virus (CCHFV), and has a complex transmission cycle that involves a wide range of hosts including mammalian and some species of birds. We implemented a seroepidemiological study in Isiolo County, Kenya, to determine relative seroprevalences of CCHFV in pastoralists, livestock and in wild animals' species. In addition, we identified subject and environment level factors that influence exposure to CCHFV. Pastoralists (n = 580) and livestock (n = 2,137) were recruited into the study through a multistage random sampling technique, and addition, various species of wild animals (n = 87) were also sampled conveniently. Serum samples from all recruited subjects were collected and screened for CCHFV antibodies using ID.vet multispecies, double-antigen IgG enzyme-linked immunosorbent assay (ELISA). The overall anti-CCHFV IgG seroprevalences in pastoralists, cattle, goats, sheep and camels were 7.2% [95% CI: 3.1–15.8%], 53.9% [95% CI: 30.7–50.9%], 11.6% [95% CI: 7.2–22.5%], 8.6% [95% CI: 3–14%] and 89.7% [95% CI: 78–94%], respectively. On average, wild animals' hosts had CCHFV seroprevalence of 41.0% [95% CI: 29.1–49.4%], and giraffes had the highest seroprevalence of 75.0% [95% CI: 63.2–79.3%]. Analysis using mixed effects logistic regression models showed that CCHFV exposure in pastoralists was significantly associated with male gender, being over 30 years and belonging to a household with a seropositive herd. In livestock, mature animals, high normalized difference vegetation indices and high vapour pressure deficit were significantly associated with CCHFV exposure. Age, sex and species of wild animals were considered as the risk factors in the analysis, but none of these variables was significant (P-value = 0.891, 0.401 and 0.664 respectively). A look at the risk factors suggests that the environmental factors such as the NDVI (P-value = 0.032) and the vapour pressure deficit (P-value = 0.004) significantly influences CCHFV exposure in livestock, while the presence of infected animals in a household significantly influences pastoralists exposure (P-value = 0.041). CCHF control in livestock, for example by applying acaricides, could minimize the risk of CCHFV exposure to pastoralists. The key findings of this study will guide policymakers in disease control, and emphasize the need for regular surveillance of zoonotic diseases for emergency preparedness, and also contributes to knowledge on One-Health approach for improved health.