Rift Valley Fever

Abstract

Rift Valley fever (RVF) is a severe veterinary disease of livestock that also causes moderate to severe illness in people. The life cycle of RVF is complex and involves mosquitoes, livestock, people, and the environment. RVF virus is transmitted from either mosquitoes or farm animals to humans, but is generally not transmitted from person to person. People can develop different diseases after infection, including febrile illness, ocular disease, hemorrhagic fever, or encephalitis. There is a significant risk for emergence of RVF into new locations, which would affect human health and livestock industries.

Keywords: Mosquitos; Rift Valley fever; Transmission; Treatment.

Figure 1. Important players in the ecology of RVF

The dynamics of RVF depends upon the complex interplay between humans, mosquitoes, wild and domesticated animals, and the environment.

Figure 2. The complex life cycle of RVF

The enzootic cycle (also known at the sylvatic or cryptic cycle; green) occurs under normal rainfall conditions. Infected Aedes mosquitoes serve as both the reservoir and vector (#1). Infectious virus can survive for years in desiccated mosquito eggs (#2). Normal rainfall leads to formation of small floodplains (dambos), in which the infected mosquito eggs hatch. Infected adult mosquitoes will then feed on and infect wild ungulates (#3); their role in transmission cycle is not well understood. Heavy rainfall conditions, such as El nino-southern oscillation events (ENSO), can lead to the epizootic cycle (also known as the domestic cycle; blue). Larger flood plains increase the likelihood of interaction between domesticated livestock and mosquitoes (#4,5), resulting in illness, abortion, and death. Other species of mosquito (Culex, Anopheles) can feed off of viremic animals and transfer the virus longer distances and to other herds (#6). Human epidemics occur when there are many infected and dying animals. People can be infected by mosquito or by handling infected animals (#7).