Rift Valley fever (RVF)

RVF is a viral zoonosis that affects mainly animals but can also cause severe disease in humans. During large outbreaks, economic losses can be significant due to the death of livestock. The virus was first identified in 1931 during an investigation into an epidemic among sheep on a farm in the Rift Valley of Kenya. Since then, Rift Valley fever (RVF) outbreaks have been reported in other parts of sub-Saharan Africa, Egypt, Saudi Arabia and Yemen. In 1997–1998, a major outbreak occurred in Kenya, Somalia and Tanzania following El Niño event and extensive flooding. Following infected livestock trade from the horn of Africa, RVF spread in September 2000 to Saudi Arabia and Yemen. RVF outbreaks in Africa are closely associated with the heavy rainfall that occurs during the warm phase of the El Niño–Southern Oscillation (ENSO) phenomenon because mosquitoes spread the zoonotic and vector-borne disease and heavy rainfall allows more mosquito eggs to hatch.

The following are standard case definitions to allow national health authorities to interpret data in an international context. However, during an outbreak case definitions may be adapted to the local context and the Red Cross Red Crescent should use those agreed/established by national health authorities. NB: Consider that during community-based surveillance, volunteers should use broad (simplified) case definitions (referred to as community case definitions) to recognize most or all possible cases, provide relevant risk communication and appropriate actions and encourage them to seek care. Other actors such as healthcare workers or investigators studying the cause of a disease, on the other hand, can use more specific case definitions that may require laboratory confirmation.

A suspected human case is defined as a person with febrile syndrome, either haemorrhagic syndrome (epistaxis, coughing or vomiting blood, blood in the stool, gingival bleeding, bruising) or meningoencephalitis, and probable contact with animals infected with RVF virus. A confirmed case of RVF is defined based on a positive laboratory test result.

WHO case definition source of information: https://www.who.int/news-room/fact-sheets/detail/rift-valley-fever

• During an outbreak of RVF, close contact with animals, particularly with their body fluids, either directly or via aerosols, has been identified as the most significant risk factor for RVF virus infection.
• Unsafe consumption of fresh blood, raw milk or animal tissue. In the epizootic regions, all animal products (blood, meat and milk) should be thoroughly cooked before eating.
• People spending time in rural areas and sleeping outdoors at night in regions where outbreaks occur.
• Animal herdsmen, abattoir workers, veterinarians and other individuals who work with animals in RVF-endemic areas.
• People increase their chances of getting the disease when they visit RVF-endemic locations during periods when sporadic cases or epidemics are occurring.
• Outbreaks of RVF in animals increase when there is no sustained programme of animal vaccination.
• Laboratory workers who may be exposed to the RVF virus.
• No proper sanitation and hygiene measures while working with infected animals or cooking.

Attack rates will vary from one outbreak to another. In case of an outbreak, consult the latest information provided by health authorities.

• Infants, young children.
• Elderly with weakened immune system.
• People with medical conditions such as high blood pressure, diabetes or heart disease and impaired immune systems.

Rift Valley fever virus.

Vector: Mosquitoes (commonly Aedes and Culex species - species varies by region) can host the virus and transmit it to livestock and humans.

Zoonotic disease: Hosts are primarily domesticated animals including cattle, sheep, camels and goats. Sheep and goats appear to be more susceptible than cattle or camels.

Humans.

• Contact transmission: Direct or indirect contact with the blood or organs of infected animals through the handling of animal tissue during slaughtering or butchering, assisting with animal births, conducting veterinary procedures, or from the disposal of carcasses or foetuses.
• Vehicle-borne transmission: Consuming raw or undercooked animal products of infected animals. Probably by ingesting the unpasteurized or uncooked milk of infected animals.
• Airborne transmission: Inhalation of Rift Valley fever virus that is in the air in the surroundings of infected animals or in laboratories.
• Vector-borne: Mosquito bite from infected mosquitoes (the dominant mosquito species varies by region).

To date, no human-to-human transmission of RVF has been documented.

Two to six days.

No human-to-human transmission of RVF has been demonstrated so far.

• Starts with fever, headache, joint pain, muscle pain, sometimes neck stiffness, sensitivity to light and diarrhoea.
• Can cause blurred or decreased vision and can lead to permanent loss of vision (ocular form).
• Some patients suffer from the loss of memory, hallucinations, confusion, disorientation, vertigo, convulsions, sleepiness and coma.
• The most severe form includes rash, jaundice and bleeding from nose and gums (haemorrhagic fever form).

Malaria, West Nile virus infection, Crimean-Congo haemorrhagic fever, Hantavirus pulmonary syndrome, dengue fever, Ebola virus disease, Lassa fever, chikungunya, yellow fever, Japanese encephalitis.

• Reverse transcriptase polymerase chain reaction (RT-PCR) assay.
• IgG and IgM antibodies enzyme-linked immunosorbent assay (ELISA).
• Virus isolation by cell culture.

Please refer to the appropriate local or international guidelines for clinical management. All clinical management including the administration of any treatment should be conducted by health professionals.

• As most human cases of RVF are relatively mild and of short duration, no specific treatment is required for these patients.
• For the more severe cases, the treatment is general supportive therapy.
• There is no vaccine against RVF for humans. However, it is possible to vaccinate animals against RVF. By preventing RVF in animals, fewer humans will be infected from mosquitoes carrying the virus or from direct contact with a sick animal.

Natural infection is likely to confer long-term protection against reinfection.