Animals > Animal Diseases > Rift Valley Fever  

Rift Valley Fever

What is Rift Valley fever?

Rift Valley fever is an acute viral disease that affects domestic animals (such as sheep, cattle, and goats) and humans. Disease in these species is characterized by fever, severe illness, abortions, and a high mortality rate. Mosquitoes are a common source of the virus.

Do we have Rift Valley fever in Canada?

No. Rift Valley fever has never occurred in Canada. It is generally found in Madagascar and regions of Africa. In the past, outbreaks of the disease occurred in Africa at 5–15 year intervals. These outbreaks occur when areas that are typically dry experience a period of heavy rainfall. An outbreak was reported in Saudi Arabia and Yemen in 2000, the first Rift Valley fever cases identified outside of Africa.

Is there a public health risk associated with this disease?

Humans are highly susceptible to the RVF virus, which is transmitted by mosquitoes. In Canada, RVF is not a threat to humans because the disease is not present. However in Africa, where the disease is known to occur, protective measures must be taken to prevent infection. Those persons at a higher risk for exposure to the virus should be vaccinated.

How is RVF transmitted and spread?

Mosquitos act as vectors (carriers), transferring the virus to livestock, on which they feed. Excessive rainfall can cause mosquito eggs that are naturally infected with the RVF virus to hatch. Infected livestock can in turn infect other mosquitos. When the disease occurs in a large number of domestic animals, the situation is referred to as an epizootic. The presence of an epizootic can lead to an epidemic among humans exposed to the diseased animals and infected mosquitos. Humans become infected from mosquito bites and possibly by other bloodsucking insects.

Laboratory tests have shown that several mosquito species can carry the virus, a few of which are found in certain regions in Canada. There are potential vectors for Rift Valley fever in Canada; however, the likelihood of them naturally transmitting the virus is low because of the regional distribution of the vectors as well as Canada’s temperate climate.

What are the clinical signs of Rift Valley fever?

Animals: Clinical signs depend on the species of animal affected and conditions such as age and pregnancy. All animals develop a fever. Pregnant livestock are severely affected by this disease and will almost always abort. Young lambs and calves develop a fever, become weak and die very suddenly. The mortality rate in young animals is very high whereas mortality in adult sheep is about 20 per cent and about 10 per cent in adult cattle. Adult sheep and cattle may have nasal discharge, excess salivation, loss of appetite, weakness, or diarrhea.

Humans: People with Rift Valley fever virus will either show no symptoms or develop a mild illness. Signs of illness include fever, weakness, back pain, dizziness, liver abnormalities, and weight loss. In some patients, the illness can progress to haemorrhagic fever, encephalitis (inflammation of the brain), or disease affecting the eyes. Approximately one per cent of humans infected with Rift Valley fever die of the disease; most people recover within four to seven days.

How is the disease diagnosed?

Rift Valley fever might be suspected in areas where the disease is known to occur based on: clinical signs, insect activity, concurrent disease in animals and humans, and rapid spread of the disease. Laboratory tests are required to confirm the diagnosis.

Are there any treatments?

There is no specific treatment for Rift Valley fever. Vaccines can be used for prevention in animals and humans in areas where the disease is endemic.

What is being done to prevent this disease from entering Canada?

Rift Valley Fever is a reportable disease under the Health of Animals Act. This means that all suspected cases must be reported to the Canadian Food Inspection Agency (CFIA). All reported suspect cases are immediately investigated by inspectors from the Agency. The CFIA imposes strict regulations on the import of animals and animal products from countries where RVF is known to occur. These regulations are enforced through CFIA port-of-entry inspections.

Canada’s emergency response strategy in the event of an outbreak of a foreign animal disease is to eradicate the disease and re-establish the country’s disease-free status as quickly as possible. In an effort to eradicate RVF, the CFIA would employ its "stamping out" policy, which would include:

• the humane destruction of all infected and exposed animals;
• surveillance and tracing of potentially infected or exposed animals;
• strict quarantine and animal movement controls;
• strict decontamination of infected premises;
• zoning to define infected and disease-free areas.
• instituting insect control measures during tick and biting fly season in the infected zone.

How to get more information?

Contact your Canadian Food Inspection Agency Area Office:

You can find your local Canadian Food Inspection Agency District Office on the CFIA Web site or by consulting the blue pages of your local phone directory.

September 2003
P0320E-03