An Explanation on Rift Valley Fever

Rift Valley Fever is an acute, fever causing viral disease most commonly observed in domesticated animals (such as cattle, buffalo ,sheep, goats), with the ability to infect and cause illness I  humans. The disease is caused by RVF virus (RVFV). It was first reported in livestock by veterinary officers in Kenya’s Rift Valley in the early 1910s. 

RVF is generally found in regions of the eastern and southern Africa where sheep and cattle are raised, including West Africa and Madagascar. Outbreaks of RVF can have major societal impacts, including significant economic losses and trade reductions. The virus most commonly affects livestock, causing disease abortion in domesticated animals, an important income source for many. Outbreaks of disease in animal populations are called “epizootics”. 

Additionally, epizootic outbreaks of RFV increase the likelihood of contact between diseased animals and humans, which can lead to epidemics of RVF in humans. One example occurred in West Africa in 1987, and was linked to construction of the Senegal River Project. The project caused flooding in the lower Senegal River area, altering ecological conditions and interactions between animals and humans. As a result, a large RVF outbreak occurred in animals and humans. Approximately 1% of humans infected with RVF die of the disease.  

By contrast, case- fatality proportions for infection causing abortion in nearly 100% of pregnancies. For humans, studies have shown that spending time in rural areas and sleeping outdoors at night in regions where outbreaks occur could be risky factor for exposure to mosquito and other insect vectors. Animal herdsmen, abattoir workers, veterinarians, and other individuals who work with potentially infected animals in RVf-endemic areas have an increased risk for infection. 

Control and Prevention 

Immunization remains the only effective way to protect livestock from RVF. The mouse neuro-adapted Smithburn strain of RVF virus can readily be produced in large quantities, is inexpensive, and induces a durable immunity 6-7 days after inoculation. It should normally not be used for protection of pregnant animals, because it may cause abortion, congenital defects and hydrops amnii in the ewe; however, its use may be contemplated during and outbreak when possible adverse effects may be outweighed by the dangers of natural infection.  

Although not proved, it is theoretically possible for the attenuated virus to revert to virulence. A small plaque variant and mutagen-induced strain have been investigated as potential vaccine candidates but have not been accepted as replacements for Smithburn strain. 

Sources: UP, Merck, FAO.