Higher Risk of Rift Valley Fever with Rainy Season Ahead

GLOBAL - FAO is advising veterinary services in sub-Saharan Africa to intensify surveillance for Rift Valley fever (RVF), which is a mosquito-borne zoonosis – affecting both animals and humans.
calendar icon 1 October 2012
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Rift Valley fever in the past has often only been detected once human cases occur. However, by heightening surveillance – for example, in sentinel animal herds – and monitoring climate data, the disease can be identified early, before the Rift Valley fever virus can be passed from animals to humans.

Recent studies have shown that the risk for RVF outbreaks increases when there is unusually heavy and persistent rainfall. The rainy season is drawing near, beginning in October in some East African countries, where the RVF risk is already higher. Humidity levels have been high in recent months, with satellite imagery showing increased vegetation growth. Combined with pools of water that lay stagnant in low-lying areas after heavy rains, it makes for the perfect habitat for breeding and newborn mosquitoes.

In addition, the El Niño weather phenomenon, in which warming sea temperatures trigger increased rainfall, has been active over the Indian Ocean. Thus the rainy season this year is predicted to be heavier than usual.

The virus is usually transmitted to humans via open skin cuts. The people at high risk of infection are those that come into direct contact with blood and tissues from infected livestock: farmers, since RVF causes abortions in pregnant animals; veterinarians who treat animals or perform necropsies; abattoir workers and butchers; and consumers who prepare raw meat for cooking.

There have been no reported cases of RVF infection in humans due to drinking raw milk or consuming insufficiently cooked meat so far, but it is generally advisable to cook milk and meat before consumption as a hygienic measure in areas where cases of RVF have been identified.

National authorities should also consider preventive vaccination in livestock herds, if effective vaccination campaign can be planned in advance and funding is available.

Rift Valley fever in humans usually causes mild to moderate, non-fatal, symptoms that are similar to those of influenza (body aches, fever, headache and nausea). Nevertheless, in a small percentage of cases, complications can lead to a life-threatening hemorrhagic fever.

When it was initially identified early in the 20th century Rift Valley Fever (RVF) was considered strictly an animal disease, infecting humans only in the rarest of cases, and it was at that time restricted to sub-Saharan Africa. In 1975, it caused the first infections in humans in South Africa, and in 1977, RVF caused a widespread outbreak in Egypt that infected more than 200 000 people and caused approximately 600 deaths, as well as significant losses in livestock.

Rift Valley fever affects valuable livestock such as cattle, buffalo sheep, goats and camels, as well as similar species of wildlife. Its damage in terms of lost income and trade can exceed several hundred million dollars, particularly in exporting countries.

The loss of animals to RVF also affects vulnerable farming communities’ food security and can result in major losses in their daily income.

In addition, Rift Valley fever has been expanding its geographic frontiers, having caused outbreaks in the Kingdom of Saudi Arabia and Yemen and more recently in the northern desert region of Mauritania.

TheCattleSite News Desk

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