Rift Valley fever - a disease that can spread with the wind

Rift Valley fever (RVF) - one of the priority diseases identified for attention by FAO's Emergency Prevention System (EMPRES) - is a mosquito-borne virus disease affecting ruminant animals and humans. It can cause very serious economic losses in livestock, particularly sheep. Goats, cattle, camels, Asian water buffaloes and possibly some wild antelopes are also susceptible.

RVF was first described in the Rift Valley of Kenya in the early 1930s but it is now endemic in restricted sites throughout much of sub-Saharan Africa. Epidemics of the disease typically occur in cycles of five to 20 years. Recent major outbreaks hit Egypt in the late 1970s and Senegal and Mauritania in 1987.

Because mosquitoes are easily carried long distances by wind, RVF has the potential to spread rapidly to new countries and even to new continents.

The first sign of an epidemic of RVF is normally numerous abortions by pregnant sheep. An exceptionally high mortality rate in new-born sheep and goats is typical, with 90 percent of lambs and kids dying after showing little more than fever, lack of appetite and weakness. In older animals, the illness can also cause vomiting, blood-stained discharge from the nose, diarrhoea and jaundice. Older animals and cattle generally recover.

In addition to becoming infected by mosquito bites, humans can also catch the virus by contact with blood or body fluids of infected animals, which may take place during slaughter or while handling aborted foetuses or animal tissues. Consumption of milk, a staple for many pastoral people, is also thought to lead to infection. The virus normally causes a non-fatal influenza-like illness in people, though potentially fatal complications such as encephalitis and haemorrhagic disease can follow. Early reports from Kenya and Somalia suggest that this epidemic is having a particularly severe effect on human beings.

22J anuary 1998

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