Seasonal Transmission Dynamics of Rift Valley Fever in Kilimanjaro Region, Tanzania

Abstract

Background: Rift Valley Fever (RVF) is a zoonotic disease that affects both animals and humans. Under reporting, misdiagnosis caused by the broad spectrum of symptoms presented by the disease, and limited access to rapid and accurate laboratory confirmation have led to an undefined burden of RVF. Reports are available that show the circulation of the virus during inter-epidemic periods, implying an endemic circulation of RVFV. This study aimed to determine RVFV transmission across annual seasons and demographic factors that are independently associated with exposure to RVFV.
Methodology: Repeated serosurveys were performed during the long rainy, short rainy, and dry seasons in Lower Moshi area of Moshi district, Kilimanjaro region from January to December 2020. The goal was to determine seroprevalence against RVFV antibodies in humans and factors associated with seropositivity. Detection of RVF antibody was performed by competitive Enzyme-Linked Immunosorbent Assays (cELISA) using serum samples. Stata statistical software version 15 was used for data analysis. Descriptive statistics was carried out, whereby categorical variables were summarised using frequencies and percentages. Numeric variables were summarised using median and interquartile range. Logistic regression was used to assess factors associated with RVF seropositivity.
Results: A total of 446 individuals were involved in the analysis. RVF seroprevalence was highest during rainy season (20.4%) and lowest in the dry season (4%). The overall annual seroprevalence of RVF was 12.8%. Season, participant age, and large number of residents in a given household were found to be significantly associated with RVF seropositivity (p<.05).
Conclusion: RVFV demonstrates an endemic circulation in Lower Moshi area of Kilimanjaro region, suggesting the site is a potential RVF hotspot. Based on this study’s findings, we recommend close surveillance of RVF in the study area and other areas with similar ecology in Tanzania as a means of preparedness for future unpredicted RVF outbreaks.