Red Cross officials say the outbreak of deadly Rift Valley Fever in Kenya has now spread from the north east to parts of the coast and central provinces.They say the numbers who have died from the disease may be double the government figure of 350 since late last year. Graham Easton of BBC Science has this report on the outbreak, and the nature of the disease.

Experts initially thought the outbreak in Kenya was due to anthrax, but now scientists from the World Health Organisation have found the Rift Valley Fever virus in samples from several human victims of the mysterious outbreak.

Rift Valley fever is a viral disease spread by mosquitoes. It's primarily an illness of livestock such as sheep, goats and camels. During epidemics in livestock the virus causes spontaneous abortions and deaths in young animals. But the disease can have devastating effects on humans too.

Symptoms include fever, vomiting and often severe bleeding

After an incubation period of about 3-6 days, the early symptoms in humans are fever and headache which can progress to bleeding from the gums and nose, and sometimes a fatal coma. Rarely the infection results in damage to the eyes, inflammation of the brain, and, as in this latest outbreak, severe bleeding.

Recent floods were a contributory factor

The virus was first isolated in 1931 during a disease outbreak in livestock on a farm in the Rift Valley of Kenya. Devastating outbreaks of Rift Valley Fever can occur when the virus is carried by mosquitoes into areas where people are not normally exposed to it, and therefore lack immunity.

The latest Kenyan outbreak was triggered by floods that brought burgeoning mosquito populations to the normally arid Garissa and Wajir districts. The last comparable outbreak, in Egypt in 1977, which affected 20 000 people, also followed flooding in normally dry areas.

Although the most important mode of spread to humans is the mosquito, humans can also be infected by direct contact with the blood of animals during slaughtering or handling of aborted foetuses.

In the latest outbreak, aid workers believe they have detected a pattern in which people handling meat, animal carcasses or aborted foetuses have been particularly prone to contracting the fever. This may explain why the epidemic has virtually been confined to the adult population.

Severe bleeding a mystery

Usually bleeding only occurs in about 5 per cent of cases. Local speculation that this is a new mutant strain of the virus is being treated with scepticism abroad.

Although World Health Organisation scientists have now found the Rift Valley Fever virus in many of the sick, it's possible that other diseases like shigellosis and malaria may partly explain the large number of deaths in the region.

Aid organisations are now calling for a public health campaign, accompanied by widespread vaccination of cattle.

The outlook for those infected remains bleak

Few have access to healthcare, and the antiviral drugs needed to fight the fever are expensive and not very effective.

The WHO aid will concentrate on controlling the mosquito population. Health workers and relatives of victims are in urgent need of rubber gloves and face masks to protect themselves. But for tourists and others hoping to travel to Kenya, the World Health Organisation is sticking by its advice that there should be no restrictions on travel to Kenya as the area affected is remote and far from the tourist centres of Nairobi, Mombasa, and the game parks.
 

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