Abstract:
BACKGROUND: Yellow fever, Dengue, West Nile and Zika viruses are re-emerging mosquito-borne Flaviviruses of
public health concern. However, the extent of human exposure to these viruses and associated disease burden in
Kenya and Africa at large remains unknown. We assessed the seroprevalence of Yellow fever and other Flaviviruses
in human populations in West Pokot and Turkana Counties of Kenya. These areas border Uganda, South Sudan and
Ethiopia where recent outbreaks of Yellow fever and Dengue have been reported, with possibility of spillover to Kenya.
METHODOLOGY: Human serum samples collected through a cross-sectional survey in West Pokot and Turkana Counties
were screened for neutralizing antibodies to Yellow fever, Dengue-2, West Nile and Zika virus using the Plaque
Reduction Neutralization Test (PRNT). Seroprevalence was compared by county, site and important human
demographic characteristics. Adjusted odds ratios (aOR) were estimated using Firth logistic regression model.
RESULTS: Of 877 samples tested, 127 neutralized with at least one of the four flaviviruses (14.5, 95% CI 12.3–17.0%),
with a higher proportion in Turkana (21.1%, n = 87/413) than in West Pokot (8.6%, n = 40/464). Zika virus
seroprevalence was significantly higher in West Pokot (7.11%) than in Turkana County (0.24%; χ
2 P < 0.0001).
A significantly higher Yellow fever virus seroprevalence was also observed in Turkana (10.7%) compared to
West Pokot (1.29%; χ
2 P < 0.0001). A high prevalence of West Nile virus was detected in Turkana County only
(10.2%) while Dengue was only detected in one sample, from West Pokot. The odds of infection with West
Nile virus was significantly higher in males than in females (aOR = 2.55, 95% CI 1.22–5.34). Similarly, the risk of
Zika virus infection in West Pokot was twice higher in males than females (aOR = 2.01, 95% CI 0.91–4.41).
CONCLUSION: Evidence of neutralizing antibodies to West Nile and Zika viruses indicates that they have been
circulating undetected in human populations in these areas. While the observed Yellow Fever prevalence in
Turkana and West Pokot Counties may imply virus activity, we speculate that this could also be as a result of
vaccination following the Yellow Fever outbreak in the Omo river valley, South Sudan and Uganda across the border
