Hemorrhagic Fevers: Fact Sheets
is Rift Valley Fever?
Rift Valley fever (RVF) is an acute, fever-causing viral disease that
affects domestic animals (such as cattle, buffalo, sheep, goats, and
camels) and humans. RVF is most commonly associated with mosquito-borne
epidemics during years of heavy rainfall.
disease is caused by the RVF virus, a member of the genus Phlebovirus in
the family Bunyaviridae. The disease was first reported among livestock
by veterinary officers in Kenya in the early 1900s.
is the disease found?
RVF is generally found in regions of eastern and southern Africa where
sheep and cattle are raised. However, RVF virus also exists in most
countries of sub-Saharan Africa and Madagascar.
virus primarily affects livestock and can cause disease in a large
number of domestic animals (this situation is referred to as an
"epizootic"). The presence of an RVF epizootic can lead to an
epidemic among humans who are exposed to diseased animals. The most
notable epizootic of RVF, which occurred in Kenya in 1950-1951, resulted
in the death of an estimated 100,000 sheep. In 1977, the virus was
detected in Egypt (probably exported there in infected domestic animals
from Sudan) and caused a large outbreak of RVF among animals and humans.
The first epidemic of RVF in West Africa was reported in 1987 and was
linked to construction of the Senegal River Project. The project caused
flooding in the lower Senegal River area and altered interactions
between animals and humans resulting in transmission of the RVF virus to
is RVF virus spread among animals?
An epizootic of RVF is generally observed during years in which heavy
rainfall and localized flooding occur. The excessive rainfall allows
mosquito eggs, usually of the genus Aedes, to hatch. The
mosquito eggs are naturally infected with the RVF virus, and the
resulting mosquitoes transfer the virus to the livestock on which they
feed. Once the livestock is infected, other species of mosquitoes can
become infected from the animals and can spread the disease. In
addition, it is possible that the virus can be transmitted by other
do humans get RVF?
Humans can get RVF as a result of bites from mosquitoes and possibly
other blood-sucking insects that serve as vectors. Humans can also get
the disease if they are exposed to either the blood or other body fluids
of infected animals. This exposure can result from the slaughtering or
handling of infected animals or by touching contaminated meat during the
preparation of food. Infection through aerosol transmission of RVF virus
has resulted from contact with laboratory specimens containing the
are the symptoms of RVF?
RVF virus can cause several different disease syndromes. People with RVF
typically have either no symptoms or a mild illness associated with
fever and liver abnormalities. However, in some patients the illness can
progress to hemorrhagic fever (which can lead to shock or hemorrhage),
encephalitis (inflammation of the brain, which can lead to headaches,
coma, or seizures), or ocular disease (diseases affecting the eye).
Patients who become ill usually experience fever, generalized weakness,
back pain, dizziness, and extreme weight loss at the onset of the
illness. Typically, patients recover within two days to one week after
onset of illness.
there complications after recovery?
The most common complication associated with RVF is inflammation of the
retina (a structure connecting the nerves of the eye to the brain). As a
result, approximately 1% - 10% of affected patients may have some
permanent vision loss.
the disease ever fatal?
Approximately 1% of humans that become infected with RVF die of the
disease. Case-fatality proportions are significantly higher for infected
animals. The most severe impact is observed in pregnant livestock
infected with RVF, which results in abortion of virtually 100% of
is RVF treated?
There is no established course of treatment for patients infected with
RVF virus. However, studies in monkeys and other animals have shown
promise for ribavirin, an antiviral drug, for future use in humans.
Additional studies suggest that interferon, immune modulators, and
convalescent-phase plasma may also help in the treatment of patients
is at risk for the illness?
Studies have shown that sleeping outdoors at night in geographical
regions where outbreaks occur could be a risk factor for exposure to
mosquito and other insect vectors. Animal herdsmen, abattoir workers,
and other individuals who work with animals in RVF-endemic areas (areas
where the virus is present) have an increased risk for infection.
Persons in high-risk professions, such as veterinarians and
slaughterhouse workers, have an increased chance of contracting the
virus from an infected animal. International travelers increase their
chances of getting the disease when they visit RVF-endemic locations
during periods when sporadic cases or epidemics are occurring.
is RVF prevented?
A person’s chances of becoming infected can be reduced by taking
measures to decrease contact with mosquitoes and other blood-sucking
insects through the use of mosquito repellents and bed nets. Avoiding
exposure to blood or tissues of animals that may potentially be infected
is an important protective measure for persons working with animals in
needs to be done to address the threat of RVF?
A number of challenges remain for the control and prevention of RVF.
Knowledge regarding how the virus is transmitted among mosquitoes and
the role of vertebrates in propagating the virus must be answered to
predict and control future outbreaks of RVF. Vaccines for veterinary use
are available, but they can cause birth defects and abortions in sheep
and induce only low-level protection in cattle. The human live
attenuated vaccine, MP-12, has demonstrated promising results in
laboratory trials in domestic animals, but more research will be needed
before the vaccine can be used in the field. In addition, surveillance
(close monitoring for RVF infection in animal and human populations) is
essential to learning more about how RVF virus infection is transmitted
and to formulate effective measures for reducing the number of
National Center for Infectious Diseases
Centers for Disease Control and Prevention, USA