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Rift Valley Fever
INTRODUCTION
Rift Valley Fever is an acute fever causing viral disease. It is responsible for severe sickness in
domestic animals but it also can affect humans thus being a zoonosis. Its effects in animals are
much more severe in animals than in humans. Rift Valley Fever is found in Africa (Eastern and
Southern parts) but outbreaks of this virus have also been reported in Madagascar and Egypt.
HISTORY
Rift Valley Fever has been linked to a sheep killing disease as early as 1913. The actual virus was
isolated in 1931 from the blood of a newborn sheep. Since then there have been several damaging
outbreaks of this virus in Southern and Northern Africa. These livestock losing outbreaks cause
substantial economic costs in this already poverty stricken region (see References: Exploring the
Environment).
STRUCTURE
Rift Valley Fever is a virus belonging to the Bunyaviridae and genus Phlebovirus. It is an
enveloped virus with a helical nucleocapsid containing negative, single stranded, (3)-segmented
RNA.
Its lipid envelope contains G1 and G2 proteins.
The virus is resistant to alkaline pH and can be inactivated by disinfectants.
REPLICATION
Main sites of replication are liver, spleen, and brain. First step of Rift Valley Fever replication
involves the interaction of G1 and G2 surface glycoproteins with the receptors on a host cell
membrane. The virus is delivered to the host cell by the means of endocytosis. The virus then
replicates using its RNA. The virions are released by exocytosis.
PATHOGENESIS
Rift Valley Fever causes disease in both animals and humans. Its animal hosts include cattle, goat,
sheep, camels, dromedaries, waterbucks, African buffalo, bats and dogs. Its incubation period can
vary from 1 to 6 days in adults and 12-36 hour in neonates. It clinical signs in animal hosts include:
elevated fever, anorexia, weakness, excessive salivation, vomiting, and diarrhea. Its fatality rate in
adults can be anything from 10% to 70%; its abortion rates can reach up to a 100%. After disease
complications are also common. They include Hepatitis, cerebral and ocular infections (see
References: Harper, K Tara).
Rift Valley Fever virus in human hosts has an incubation period of 2 to 6 days. Its clinical signs in
humans can vary. Some individuals have no symptoms however in some the illness can have flulike symptoms which include sudden onset of fever, nausea, weakness, back and abdominal aches
and photophobia. Although most infected individuals fully recover in 2 to 7 days, a small
percentage of patients develop complications. Ocular lesions often leading to loss of vision,
Meningoencephalitis, and Hemorrhagic fever are all possible complications of Rift Valley Fever.
Fatalities resulting from this virus are rare in humans (approximately 1%) (see References: Harper,
K Tara)
EPIDEMIOLOGY
Rift Valley Fever virus distribution has been limited to the Northern, Southern, and Eastern parts
of Africa as well as Saudi Arabia (single outbreak, 2000) and Yemen (single outbreak, 2000) (see
References: Exploring the Environment). In the early 1930’s the outbreaks of the Rift Valley Fever
have been linked to severe rainfalls and floods causing us to believe that the main vectors of this
virus are mosquitoes as well as other blood suckling insects (sand flies). Blood, body fluids and
raw milk of infected animals are also modes of transmission. Airborne transmission among some
laboratory workers has also been reported.
Kenya’s Rift Valley’s geologic features such as dambos (located near rivers shallow depressions
were water collects) contribute greatly to breeding of mosquitoes and subsequently to the spread
of the virus (see References: Exploring the Environment).
High risk individuals for infection include slaughterhouse workers, farmers, and veterinarians,
others who handle blood or tissues of infected animals as well as individuals who sleep or spend
prolonged time outside near stagnant water.
LABORATORY DIAGNOSIS
The diagnosis of the Rift Valley Fever may be reached using various laboratory techniques. The
presence of specific IgM antibodies to this virus may be demonstrated when using enzyme-linked
immunoassay (ELISA) test. Other successful diagnostic techniques for Rift Valley Fever include:
PCR, immunofluuresence, and antigen detection (see References: Vidyya, Medical News Service).
TREATMENT
No known cure for the Rift Valley Fever is known. However studies with Ribavirin as well as
Interferon, Immune Modulators, and Convalescent Phase Plasma are bringing promising results
for humans.( see References: CDC) There is no known therapy for infected animal hosts.
PREVENTION AND CONTROL
There are available vaccines which greatly reduce the chance for infection in animals. The live
vaccine when given to an animal immunizes it for a period of three years. However it should not
be given to animals that are or may be pregnant because of its high abortion causing rate. The
killed vaccine does not cause these effects however it requires two inoculations. In order to produce
effective immunity annual revaccinations of the killed vaccine are needed (see References: World
Organization for Animal Health). Other prevention in animals includes: constant surveillance of
livestock for health assessment, taking the proper quarantine steps when importing animals, rapid
burial of infected bodies. Vector control such as removal of stagnant waters and massive
application of insecticides during rainy seasons should also be taken into consideration.
Because Rift Valley Virus causes only minor symptoms in humans vaccines are not available.
However other preventive measures can be taken to stop the cycle of this virus. Protecting you
from mosquitoes (window and door screens, bed nets, and mosquito repellants), minimalizing
direct contact with animals, good hygiene and wearing protective gear and clothing when handling
infected animals or tissues, those are all the measures that should be taken into consideration when
present in regions where infection can occur.
REFERENCES
CDC. Special Pathogens Branch. Retrieved 20 June, 2004
< http://www.cdc.gov/ncidod/dvrd/spb/mnpages/dispages/rvf.htm>
CIDRAP- Centers for Infectious Disease, Research and Policy. Retrieved 20 June, 2004
<http://www.cidrap.umn.edu/index.html>.
Exploring the Environment: Rift Valley Fever. Retrieved 20 June, 2004
< http://www.cotf.edu/ete/modules/rift/rvbackgroundinfo.html>.
Harper, K. Tara. TKH Virology Notes: Rift Valley Fever. Retrieved 20 June, 2004
< http://www.tarakharper.com/v_rift.htm#des>.
Vidyya
Medical
News
Service.
2004 <http://www.vidyya.com/archives/0921_5.htm>
Retrieved
20
June,
World Organization for Animal Health. Rift Valley Fever. Retrieved 20 June, 2004
< http://www.tarakharper.com/v_rift.htm#des>
Prior to writing this paper I have read all of the articles listed above thus the paper is a compilation
of
my
knowledge
taken
and
learnt
from
those
articles.
2
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