Serologic Evidence of Exposure to West Nile Virus among Humans in Ibadan, Southwestern Nigeria

Abstract

Background: Cases of fever without diagnoses of malaria and/or typhoid are usually regarded as undifferentiated febrile illness (UFI) in Nigeria. We studied the contribution of WNV (an arbovirus) to UFI in humans in southwestern Nigeria.

Materials and methods: Sera from 188 consenting humans visiting two health care facilities in Ibadan, and 25 horse grooms from Lagos and Ibadan were screened for WNV antibodies by cELISA and a subset by PRNT. Pertinent demographic/clinical data were collected and blood samples screened for Plasmodium spp, Salmonella typhi and S. paratyphi antibodies. Student’s t-test and binary logistic regression were used for data analysis.

Results: Overall, 156 participants (73.2%, 95% CI: 67.3-79.2 [n=213]) were positive for WNV antibodies. Being clinically ill was associated (p=0.001) with WNV seropositivity while “active” and “non-active” participants had comparable (p=0.21) seroprevalence of 74.6% and 62.5%, respectively. Forty-five percent (18/40) of febrile participants had WNV antibodies only, thereby accounting for UFI. The 18-66 year olds had higher (75.8%) seroprevalence than those ≤ 17 years (47.4%) while seropositivity obtained for the horse grooms (56.0%) was significantly lower than for the remaining 188 individuals (75.5%). Participants were mostly exposed to WNV (75.5%) than Plasmodium (33.5%) and S. typhi (39.9%) while PRNT showed that 10.5% of tested humans had protective WNV antibodies.

Conclusions: This study revealed serologic evidence of exposure of the participants to WNV and contribution of the virus (or related flaviviruses) to UFI in the study area. High prevalence of the antibodies indicates endemicity of southwestern Nigeria for WNV.

Key words: Humans, anti-WNV antibody, prevalence rate, undifferentiated febrile illness, southwestern Nigeria.