3. Rift Valley Fever (RVF) is an arthropod-borne,
acute, fever-causing viral disease of sheep, goats,
cattle, buffalo, camels and people.
Infection with RVF virus may cause abortion of
pregnant animals and high mortality rate in young
livestocks. In humans, it usually causes an influenza-
like disease but occasionally leads to more serious
complications with high morbidity and mortality.

4. *The RVF virus belongs to the family
bunyaviridae, genus phlebovirus.
*There is only one serotype of RVF
virus.
*Stable at
*-60oC to 23 C
*50-85% relative humidity
*Inactivated
*Lipid solvents
*Detergents
*Low pH

5.  Rift Valley Fever was first
reported at Lake Naivasha in
Kenya (1931).
 There were many sheep
abortions and young lambs
were found sick or dead.

7. *Generally found in eastern and southern Africa where
sheep and cattle are raised.
*Most countries of sub-Saharan Africa.
*Madagascar.
*September 2000 RVF outbreak in Saudi Arabia and
Yemen – first outbreak outside of the African
continent.

10. Date Country
1950-1951 Kenya
1967-1970 Nigeria
1969 Central African Republic
1976-1977 Sudan
1977-1980 Egypt
1987 Mauritania
1990-1991 Madagascar
1993 Egypt – Senegal
1997 Kenya – Somalia
1999 South Africa
2000-2001 Saudi Arabia - Yemen

12. Disease reported present
Disease reported absent
Data unavailable or incomplete

15. The reservoir for RVF is:
Mosquitoes – Aedes species
* Transovarial transmission.
* Eggs dormant in soil for long
periods.
* Heavy rainfall, eggs hatch.
Ruminants serve as an amplifying
host once it affected.

16. Infected livestock (sheep, cattle, goats) can have high
levels of viremia which is sufficient to infect various
mosquito vectors. These amplifying hosts help the
disease become established in the environment and can
lead to large epizootic epidemics.

19. RVF is primarily transmitted from
animal to animal by a mosquitoes.
Other arthropods (Stomoxys, midges
and tabanids) are able to transmit RVF
by mechanical means.

20. Village butchers are at risk

21. Veterinarians and Livestock handlers are at risk

22. Ingestion of raw milk

23.  PATHOGENESIS
 Hepatocytes are the primary site of viral replication in
lambs and calves.
 In very young animals, hepatic lesions progress from
degeneration and necrosis of individual hepatocytes to
extensive necrosis throughout the liver resulting in
hepatic insufficiency and failure.
 In young animals, encephalomyelitis may also occur.

24. Incubation period less
than 3 days
Early signs
Fever 40-41°C
Loss of appetite
Jaundice
Weakness

25. *High rate of abortion at any stage of gestation
In pregnant ewes, abortion may approach 100%
Aborted fetus is usually autolyzed.

26. *Ewe may also retain the placenta.
*Endometritis is another complication after aborting
the fetus.

27. Encrustation around the
muzzle.
Some develop
diarrhea.

28. *Acute death may occur in
20-30% of adults.
 Heavy sheep losses
occur during epidemic.

29. *Newborn Lambs, Kids: Most severe in young
lambs under 2wks old (mortality has high as
90%).
*Fever (40-42 C).
*Anorexia.
*Weakness.
*Disinclination to move or feed.
*Evidence of abdominal pain, and rapid respiration.
*Death may occur within 24 to 36 hours after the
first signs appear.

30. Calves:
 Fever (40-41 C).
 Depression.
 Mortality rate: 10-70%
 Death occurs about 2-8 days after the first
signs appear.

31. Symptoms may be prolonged and will include
jaundice in some calves.
Aborted calves are moderately autolyzed.

32. Adults:
 Fever (40-41 C).
 Excessive salivation.
 Anorexia and weakness.
 Fetid diarrhea.
 Fall in milk yield.
 Abortion may reach 85% in the herd.
 Mortality rate is usually less than 10%.

33. Camels (in Egypt) inapparent disease except abortions.
Dogs
*Abortion up to 100%
*Severe disease and death in puppies
Cats: Death in kittens
Horses: Viremia but resistant
Pigs: Resistant
Birds: Refractory

34.  Focal or generalized hepatic necrosis.
 Congestion, enlargement, and
discoloration of liver with sub-capsular
hemorrhages.
 Brown-yellowish color of liver in aborted
fetuses.

36.  Hemorrhagic enteritis.
Mucosal haemorrhages
in the abomasum.

37.  Spleen with subcapsular
haemorrhages.
 Haemorrhagic and
oedematous lymph node.

38.  Haemorrhages and oedema of the wall of the gall
bladder are common, and the lumen may contain a
blood coagulum or blood-tinged bile.
Blood coagulum in gall Haemorrhagic and oedematous Gall bladder with blood-tinged bile
bladder gall bladder wall

39. Suspect RVF when heavy rains are followed by:
 High mosquito populations.
 Abortions in pregnant animals.
 High mortalities in young animals.
 Extensive hepatic necrosis.
 Frequently there is also an influenza-like illness in
farm workers and people handling infected
carcasses.

40.  Specimens
Specimens to be submitted for laboratory confirmation of
the diagnosis include:
 Heparinized blood from animals with high fever.
 Serum of live affected animal.
 Tissue samples including:
 Liver, spleen, kidney and lymph nodes of dead
animals.
 Liver, spleen and brain from aborted foetuses.

41.  Specimens should be securely packaged and
submitted on ice to a suitable laboratory for
isolation of virus or demonstration of antibody.
 Where delay in getting specimens to the
laboratory is unavoidable or where material has
to be transported at ambient temperature, tissue
samples can be preserved in glycerol-saline
solution.

42. Virus isolation
Virus can be isolated readily in a variety of cell cultures,
or in suckling and weaned mice or hamsters inoculated
intracerebrally or intraperitoneally.
Serology
In animals that survive the disease, paired serum samples,
one taken during the acute illness and the other 2 - 3
weeks later, should be submitted for antibody tests by
tests such as CF, ID, serum neutralization or ELISA.

43.  RFV antigen detection
RT-PCR identification of RVF virus.
Virus isolation in tissue cultures or inoculated animals,
 Microscopic pathology
Tissue specimens from the liver, spleen, and lymph
nodes should also be collected in 10% buffered-
formalin for histopathological examination.

45. Nairobi sheep disease:
 No hepatitis, not in newborn lambs.
Bluetongue:
 Foot lesions (coronitis) and also no hepatitis.
Heartwater:
 Serous fluids in body cavities and neurological
signs.
Ephemeral fever:
 Recumbency and rapid recovery.

46. Wesselbron:
 Less severe than RVF.
 Toxoplasmosis, leptospirosis, brucellosis, Q fever
and salmonellosis:
 They are not associated with rainfall, nor do they
produce such high neonatal mortality.

47. 1. Vaccination Program
• Immunization is the most effective method of
controlling the disease.
• The current vaccine can be abortigenic and
teratogenic so not recommended for pregnant
animals.

49.  The recorded problems include hydrops amnii,
arthrogryposis, hydranencephaly, and
microencephaly.
Hydrops amnii following inoculation with Ewe. Hydrops amnii.
Smithburn vaccine There may be up to 20 litres of fluid

50. Hydranencephaly Arthrogryposis and anasarca

51. 2. Vector Control

52. 3. Wear personal protective equipment (gloves, coveralls
and boots) when handling aborted fetuses or performing
necropsies.

53. 4. Disinfect animal housing areas that has become
contaminated with RVF virus.
 The RVF virus is easily destroyed by
disinfectants.