Inter-epidemic Rift Valley fever virus infection incidence and risks for zoonotic spillover in northern Tanzania.

Journal Article (Journal Article)

Rift Valley fever virus (RVFV) is a mosquito-borne pathogen that has caused epidemics involving people and animals across Africa and the Arabian Peninsula. A number of studies have found evidence for the circulation of RVFV among livestock between these epidemics but the population-level incidence of infection during this inter-epidemic period (IEP) is rarely reported. General force of infection (FOI) models were applied to age-adjusted cross-sectional serological data to reconstruct the annual FOI and population-level incidence of RVFV infection among cattle, goats, and sheep in northern Tanzania from 2009 through 2015, a period without reported Rift Valley fever (RVF) cases in people or animals. To evaluate the potential for zoonotic RVFV spillover during this period, the relationship between village-level livestock RVFV FOI and human RVFV seropositivity was quantified using multi-level logistic regression. The predicted average annual incidence was 72 (95% Credible Interval [CrI] 63, 81) RVFV infections per 10,000 animals and 96 (95% CrI 81, 113), 79 (95% CrI 62, 98), and 39 (95% CrI 28, 52) per 10,000 cattle, sheep, and goats, respectively. There was variation in transmission intensity between study villages, with the highest estimated village-level FOI 2.49% (95% CrI 1.89, 3.23) and the lowest 0.12% (95% CrI 0.02, 0.43). The human RVFV seroprevalence was 8.2% (95% Confidence Interval 6.2, 10.9). Human seropositivity was strongly associated with the village-level FOI in livestock, with the odds of seropositivity in an individual person increasing by around 1.2 times (95% CrI 1.1, 1.3) for each additional annual RVFV seroconversion per 1,000 animals. A history of raw milk consumption was also positively associated with human seropositivity. RVFV has circulated at apparently low levels among livestock in northern Tanzania in the period since the last reported epidemic. Although our data do not allow us to confirm human RVFV infections during the IEP, a strong association between human seropositivity and the FOI in cattle, goats, and sheep supports the hypothesis that RVFV circulation among livestock during the IEP poses a risk for undetected zoonotic spillover in northern Tanzania. We provide further evidence for the likely role of raw milk consumption in RVFV transmission from animals to people.

Full Text

Duke Authors

Cited Authors

  • de Glanville, WA; Nyarobi, JM; Kibona, T; Halliday, JEB; Thomas, KM; Allan, KJ; Johnson, PCD; Davis, A; Lankester, F; Claxton, JR; Rostal, MK; Carter, RW; de Jong, RMF; Rubach, MP; Crump, JA; Mmbaga, BT; Nyasebwa, OM; Swai, ES; Willett, B; Cleaveland, S

Published Date

  • October 2022

Published In

Volume / Issue

  • 16 / 10

Start / End Page

  • e0010871 -

PubMed ID

  • 36306281

Pubmed Central ID

  • PMC9665400

Electronic International Standard Serial Number (EISSN)

  • 1935-2735

Digital Object Identifier (DOI)

  • 10.1371/journal.pntd.0010871


  • eng

Conference Location

  • United States