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. 2019 May 17;16(1):65.
doi: 10.1186/s12985-019-1176-y.

Serological evidence of Flavivirus circulation in human populations in Northern Kenya: an assessment of disease risk 2016-2017

E Chepkorir  1   2 , D P Tchouassi  3 , S L Konongoi  4 , J Lutomiah  4 , C Tigoi  3 , Z Irura  5 , F Eyase  6 , M Venter  7 , R Sang  3
Affiliations

Serological evidence of Flavivirus circulation in human populations in Northern Kenya: an assessment of disease risk 2016-2017

E Chepkorir et al. Virol J. .

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%; χ2 P < 0.0001). A significantly higher Yellow fever virus seroprevalence was also observed in Turkana (10.7%) compared to West Pokot (1.29%; χ2 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.

Keywords: Dengue virus; Flaviviruses risk assessment; Northern Kenya; Plaque reduction neutralization test; Seroprevalence; West Nile virus; Yellow fever virus; Zika virus.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
Map of Kenya showing the study sites in West Pokot and Turkana Counties. This map was generated specifically for this manuscript by icipe GIS team and does not infringe on copyright issues. The sample points were collected using a GPS gadget (garmin etrex 20, https://buy.garmin.com/en-US/US/p/518046), and the county boundaries for Kenya derived from AfricaOpendata (https://africaopendata.org/dataset/kenya-counties-shapefile, license Creative Commons)
Fig. 2
Fig. 2
Seroprevalence of the various Flaviviruses presented separately for each county. The error bars indicate Agresti-Coull 95% confidence intervals. The number of samples tested was 413 in Turkana and 464 in West Pokot
Fig. 3
Fig. 3
Proportions positive for three most prevalent viruses (ZIK, YF and WN) by age group for (a) West Pokot (n = 464) and (b) Turkana (n = 413) counties. The error bars indicate Agresti-Coull 95% confidence intervals
See this image and copyright information in PMC

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