Rift Valley Fever (Animal)

Unique identifier / Notation

BI0082

Synonyms

Infectious enzootic hepatitis of sheep and cattle.

Rift Valley fever (RVF) is an acute haemorrhagic viral disease, affecting small and large ruminants and camels. RVF virus is a member of the Phlebovirus genus. The disease causes high mortality especially in new borne and mass abortions in pregnant animals. Humans become infected from contact with tissues/blood of infected animals including abortive material and through mosquito bites. Disease in humans presents as influenza like illness, haemorrhagic fever, encephalitis and occasionally death (adapted from FAO, 2003; WHO, 2018; OIE 2020).

Primary reference(s)

FAO, 2003. Recognizing Rift Valley fever. Animal Health Manual No. 17. Food and Agriculture Organization of the United Nations (FAO). Accessed 4 October 2020.

OIE, 2020. Rift Valley Fever (RVF). World Organisation for Animal Health (OIE). Accessed 4 October 2020.

WHO, 2018. Newsroom Fact Sheet Rift Valley fever. World Health Organization (WHO). Accessed 4 October 2020.

Additional scientific description

Rift Valley fever (RVF) is a viral zoonosis that primarily affects animals but also has the capacity to infect humans. Infection can cause severe disease in both animals and humans (WHO, 2018).

RVF is an economically important disease, and affects different species of animals and humans. Immunisation and vector control are the main strategies to reduce the incidence of RVF. It is considered an occupational disease of livestock handlers, dairy farmers, abattoir workers and veterinarians. The direct socio-economic impact of RVF is on livestock producers due to high levels of mortality and morbidity in animals (WHO, 2018).

RVF virus is a member of the Phlebovirus genus. The virus was first identified in 1931 during an investigation into an epidemic among sheep on a farm in the Rift Valley of Kenya (WHO, 2018). Since then, outbreaks have been reported in sub-Saharan Africa. In 1977 an explosive outbreak was reported in Egypt, the RVF virus was introduced to Egypt via infected livestock trade along the Nile irrigation system. In 1997–1998, a major outbreak occurred in Kenya, Somalia and Tanzania following an El Niño event and extensive flooding. After infected livestock trade from the horn of Africa, RVF spread in September 2000 to Saudi Arabia and Yemen, marking the first reported occurrence of the disease outside the African continent and raising concerns that it could extend to other parts of Asia and Europe (WHO, 2018).

RVF is a disease of caused by RVF virus (RVFV), an arbovirus, transmitted by Aedes mosquitoes. RVF epidemic/epizootic has been associated with periods of flooding following heavy rainfall especially after a long drought. These floods create pools of water conducive for hatching/emergence of Aedes mosquitoes, which may be infected with the RVFV and can transmit the virus to ruminants or camels when they drink from or feed close to the water pools (FAO, 2003).

Outbreaks of RVF in animals can be prevented by a sustained programme of animal vaccination. Commercially available veterinary RVF vaccines are important for preventing the spread of RVFV in endemic countries. Three live-attenuated RVF vaccines are available for veterinary use in endemic areas. However, these vaccines have adverse effects in pregnant ewes, resulting in abortion or malformation. On the other hand, three different inactivated RVF vaccines that induce short-term immunity are also available in endemic regions (FAO, 2003).

Rift Valley fever outbreaks in domesticated animals are often accompanied by human disease. The majority of human infections result from contact with the blood or organs of infected animals. Human infections have also resulted from the bites of infected mosquitoes. To date, no human-to-human transmission of RVF virus has been documented (WHO, 2018).

The most common form of the disease in humans is a self-limiting, flu-like illness. Complications in a minority of cases include ocular disease, neurological signs, kidney dysfunction and a life-threatening haemorrhagic syndrome with hepatic dysfunction. Although overall case fatality rates are thought to be low (≤2%), there may be a very large number of cases during some epidemics, resulting in hundreds of serious cases and significant numbers of deaths (Spickler, 2015).

Metrics and numeric limits

None found.

Key relevant UN convention / multilateral treaty

International Health Regulations (2005), 3rd ed. (WHO, 2016).

WTO Agreement on the Application of Sanitary and Phytosanitary Measures (SPS Agreement) (WTO, 1994).

UN Recommendations on the Transport of Dangerous Goods - UN Model Regulations Model Regulations Nature, Purpose and Significance of the Recommendations (UNECE, no date).

Examples of drivers, outcomes and risk management

Drivers: RVF-infected mosquitoes; flash floods caused by unusual rainfall in an area where RVF occurred in the past; lack of biosecurity in handling aborted foetuses/slaughtered carcasses.

Outcomes: Abortion and/or death of infected animals and humans, spread of infection, trade ban.

Risk management: Vaccination programme, movement control, improved biosecurity, waterbody management.

As an example of a coordinated response, in the 2016 Niger outbreak, the World Health Organization (WHO) sent a multisectoral national rapid response team, including members from the Ministry of Health, veterinary services and Centre de Recherche Médicale et Sanitaire (CERMES). The unit was deployed for field investigation on 31 August 2016. In Niger, the WHO Country Office provides technical and financial support for surveillance, outbreak investigation, technical guidelines regarding case definition, case management, shipment of samples, and risk communication. The Food and Agriculture Organization of the United Nations (FAO), the World Organisation for Animal Health (OIE), and the WHO are coordinating on animal and human health and providing additional support to Niger for the outbreak response (WHO, 2018).