Rift Valley Fever in Ruminants

1A PHLEBOVIRUS of the familiy Bunyaviridae is the viral agent of Rift Valley Fever, an arthropod-borne viral disease seen in Africa and the Arabian Peninsula that can cause high mortality particularly in new-born lambs and kids and abortion in adult sheep, goats and cattle. This virus causes a hemorrhagic fever syndromes in humans.

Bovine, fetus. The skin of this emphysematous fetus is stained with meconium.

Rift Valley fever (RVF) is a peracute or acute zoonotic disease of domestic ruminants in Africa and, recently, the Arabian Peninsula.

Signs of the disease tend to be nonspecific, rendering it difficult to recognize individual cases. During epidemics, the occurrence of numerous abortions and deaths among young animals, together with an influenza-like disease in humans, tends to be characteristic.

Rift Valley fever (RVF) is a zoonotic, arthropodborne viral disease important in domestic ruminants. This disease is characterized by high mortality rates in young animals and abortions in pregnant ruminants. Rift Valley fever is endemic in sub-Saharan Africa. Epidemics occur in this region when heavy rainfalls cause infected mosquito eggs to hatch, and large numbers of susceptible animals are present. Rift Valley fever first ap-peared outside Africa in 2000, when outbreaks were reported in Saudi Arabia and Yemen.Rift Valley fever epizootics are often accompanied by human disease. Many human cases are caused by occupational exposure to blood and tissues from infected animals, but mosquito-borne transmission can cause epidemics. The most common form of the disease is a self-limiting, flu-like illness; however, ocular disease and rare cases of fatal hemor-rhagic fever also occur.Rift Valley fever can affect many species of animals in-cluding sheep, cattle, goats, buffalo, camels, and monkeys, as well as gray squirrels and other rodents. The primary ampli-fying hosts are sheep and cattle. Viremia without severe dis-ease may be seen in adult cats, dogs, horses and some mon-keys, but severe disease can occur in newborn puppies and kittens. Rabbits, pigs, guinea pigs, chickens and hedgehogs do not become viremic.2

RVF should be suspected when abnormally heavy rains are followed by the widespread occurrence of abortions and mortality among newborn animals characterized by necrotic hepatitis, and when hemorrhages and influenza-like disease are seen in people handling animals or their products. Histopathologically, the liver lesions in lambs are pathognomonic. The virus can readily be isolated from tissues of aborted fetuses and the blood of infected animals. The viral titer in these tissues is often high enough to use organ suspensions as antigen for a rapid diagnosis in neutralization, complement fixation, ELISA, agar gel diffusion tests, or staining of organ impression smears; however, these tests should be supplemented by isolation in suckling mice or hamsters injected intracerebrally or in cell cultures such as baby hamster kidney (BHK21), monkey kidney (Vero), CER and mosquito cells, or primary kidney and testis cell cultures of lambs. Detection of viral nucleic acid by PCR is possible, and 2 reverse transcriptase-PCR tests have been described.

All conventional serologic tests can be used to detect antibody against RVF virus and are helpful in epidemiologic studies. In some areas, however, serologic surveys may be complicated by cross-reactions between RVF virus and other phleboviruses. An IgM ELISA can demonstrate recent infection using a single serum sample.