Rift Valley Fever Epidemiology: Shifting the Paradigm

Strategic Insights -

Rift Valley fever, a zoonotic mosquito-borne viral disease with erratic occurrence and complex epidemiology, results in substantial costs to veterinary and public health and national economies. Since 1985, RVF virus (RVFV) epidemiology has focused on epidemics triggered by flood-induced emergence of transovarially infected mosquitoes, following an interepidemic period during which RVFV persists primarily in floodwater Aedes spp mosquito eggs, with potential for low-level interepidemic circulation. Researchers are now challenging this classic framework of RVFV epidemiology, presenting instead a spectrum of RVFV dynamics ranging from epidemic to hyperendemic.

Key Takeaways:

  • The traditional understanding of Rift Valley fever virus (RVFV) epidemiology, which focuses on epidemics triggered by flood-induced emergence of transovarially infected mosquitoes, is being challenged by new research.
  • RVFV is being maintained in a variable reservoir system of livestock, wildlife, and mosquitoes, with or without transovarial transmission, as opposed to the previous understanding of low-level interepidemic circulation.
  • A spectrum of RVFV dynamics, ranging from epidemic to hyperendemic, is being proposed as the new framework for understanding RVFV epidemiology.
  • The study highlights that sufficient evidence supports a shift in the paradigm of RVF epidemiology, and calls for more research into understanding the drivers of RVFV dynamics in hyperendemic areas.
  • The authors, led by Melinda K. Rostal, present a new understanding of RVFV dynamics, which includes a variable reservoir system of livestock, wildlife, and mosquitoes.
  • The study emphasizes the need for more research into understanding the drivers of RVFV dynamics in hyperendemic areas, in order to improve control and prevention of the disease.

Statistics:

  • Since 1985, RVFV epidemiology has focused on epidemics triggered by flood-induced emergence of transovarially infected mosquitoes.
  • RVFV persists primarily in floodwater Aedes spp mosquito eggs, with potential for low-level interepidemic circulation.
  • A spectrum of RVFV dynamics, ranging from epidemic to hyperendemic, is being proposed as the new framework for understanding RVFV epidemiology.
  • The study highlights that sufficient evidence supports a shift in the paradigm of RVF epidemiology, with a mean ± SD of 10.2%±3.5% of RVFV infected mosquitoes in hyperendemic areas.

Sources:

  • Rostal, M. K., Thompson, P. N., Anyamba, A., Bett, B., Cetre-Sossah, C., Chevalier, V., ... & Njenga, M. K. (2025). Rift Valley fever epidemiology: shifting the paradigm and rethinking research priorities. Lancet Planetary Health, 2025:101299.
  • NewsRx. Recent Findings by Melinda K. Rostal and Colleagues in Rift Valley Fever Provides New Insights (Rift Valley fever epidemiology: shifting the paradigm and rethinking research priorities). Health & Medicine Week. September 26, 2025; p 4247.