Serologic evidence of silent Rift Valley fever virus infection among occupationally exposed persons in northern Nigeria

Introduction: Rift Valley fever (RVF) is a zoonotic disease caused by RVF virus (RVFV) and transmitted primarily by mosquitoes and contact with fluids and tissues of infected animals. First described in Kenya, it has spread to many African countries and beyond. In humans, it is sometimes misdiagnosed because the symptoms resemble those of influenza and/or malaria. Butchers, abattoir workers, and livestock keepers have the highest risk of infection. Methodology: In this study, serum samples collected between February and September 2019 from 196 individuals comprising of butchers (n = 121), abattoir/slaughterhouse workers (n = 55), and livestock keepers (n = 20) in Benue, Sokoto, and Borno States of northern Nigeria were screened using a commercial ELISA that detected anti-RVFV IgM and IgG alike (i.e., without discrimination). Data from administered questionnaires and the ELISA results were statistically analyzed. Results: Thirty-nine (19.9%) of the 196 samples were positive for RVFV antibodies. The distribution by states showed that 17.4% (8/46), 21.7% (15/69), and 19.8% (16/81) of samples from Benue, Sokoto, and Borno States were seropositive, respectively. Additionally, 21.5% (26/121) butchers, 16.4% (9/55) abattoir workers, and 20% (4/20) livestock keepers were seropositive. Conclusions: These findings provide serological evidence for exposure of occupationally at-risk individuals in northern Nigeria to RVFV. The higher seropositivity obtained in Sokoto and Borno states could be due to contact of these individuals with infected animal blood/tissues, aborted fetuses, and unhindered transboundary movement of animals and animal products into these states which share international borders with Niger, Chad, and Cameroon where evidences of RVFV infections were recently reported.