RVF by Ahmed kadle
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Rift Valley Fever is a viral disease that affects sheep, goats, cattle and humans. It is transmitted by mosquitoes and can cause high rates of abortion and death in young animals. In humans, it typically causes an influenza-like illness but can sometimes lead to more serious complications. The virus was first identified in Kenya in 1931 after an outbreak with many sheep abortions and sick or dead young lambs. Vaccination and vector control are important for controlling the spread of the disease.
RVF by Ahmed kadle
- 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
- 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.
Editor's Notes
- #6: Lake naivasha:part of the Great Rift Valley
- #12: The blue areas indicate African countries with endemic disease and substantial outbreaks of RVF. The green areas are countries know to have some cases, periodic isolation or serological evidence of RVF.
- #15: Birds - refractory, no virus isolation
- #19: Aerosol Transmission to Humans:- Virus aerosolized during butchering or necropsy of infected animals.Laboratory workers, Livestock handlers and butchers have the highest risk.
- #40: One should suspect RVF when heavy rains are followed by the occurrence of abortions in sheep, goats and cattle together with fatal disease, particularly in young animals, which is marked by necrotic hepatitis and haemorrhages in the abomasum and serosal surfaces. Frequently there is also an influenza-like illness in farm workers.
- #41: Samples from aborted foetuses should include brain since this is usually less autolysed or putrefied than viscera.
- #46: Ephemeral does not produce any disease in sheep, goat and young cattle.
- #47: Rift Valley fever should be differentiated from Wesselsbron disease as both diseases can cause mortality in new-born lambs and kids and abortion in ewes. However, RFV is associated with much higher mortality and abortion rates than Wesselsbron disease.
- #48: Immunization of sheep, goats and cattle is the most effective method of controlling the disease. The current vaccine can be abortigenic and teratogenic but is usually less than the effect of the disease.
- #51: Hydranencephaly(mid-brain and medulla partially developed) Arthrogryposis, anasarca and spina bifidaAnasarca, also known as "extreme generalized edema.Spina bifida (Latin: "split spine") is a developmental congenital disorder caused by the incomplete closing of the embryonic neural tube.