Rift Valley Fever (RVF) Prepared by Dr. Ghalib S. Ridha Visiting Assistant professor of Internal medicine & Infectious diseases. Dept. of Internal Medicine Faculty of Veterinary Medicine Al-Fateh university Tripoli, LIBYA 07/08/2009 Dr. Ghalib's Lectures. is a peracute to acute zoonotic febrile disease of domestic ruminants, cattle, buffalo, sheep, goat and camel in Africa. Epidemic of RVF is characterized by - Occurrence of numerous abortions - Deaths among young animals - Influenza-like disease in man. The disease is caused by the RVF virus (3 strains) a member of the genus Phlebovirus in the family Bunyaviridae, can be grown in tissue culture and embryonated eggs and can be attenuated by serial passages through mouse brains. 07/08/2009 Dr. Ghalib's Lectures. It Rift Valley Fever (RVF) Epidemiology The disease was first reported among livestock in Kenya in the early 1900s. RVF is generally found in regions of eastern and southern Africa where sheep and cattle are raised, but the virus also exists in most countries of subSaharan Africa and in Madagascar. In September 2000, a RVF outbreak was reported in Saudi Arabia and subsequently Yemen. These cases represent the first Rift Valley fever cases identified outside Africa. 07/08/2009 Dr. Ghalib's Lectures. A cyclic epidemics have occurred at 5- to 20 years intervals. The cycles are normally associated with periods of abnormally heavy rainfall. In the periods between epidemics, the virus is believed to be dormant in eggs of the mosquito in the dry soil. With adequate rainfall, the infected mosquitoes develop and infect ruminants in which the virus multiply. The incidence of RVF peaks is in late summer. Pathogenesis RVF virus causes destruction of liver cells with acute hepatic insufficiency also capable of causing encephalomyelitis. 07/08/2009 Dr. Ghalib's Lectures. How do humans get RVF? Humans usually get RVF through bites from infected mosquitoes and possibly other biting insects. Humans can also get the disease if they are exposed to the blood, body fluids, or tissues of infected animals. Direct exposure to infected animals can occur during slaughter or through veterinary and obstetric procedures. Infection through aerosol transmission of RVF virus has occurred in the laboratory environment. 07/08/2009 Dr. Ghalib's Lectures. Clinical findings After an incubation period of 12-36 hr, a sudden onset of fever may develop followed by incoordination, collapse and sudden death within 36 hr in 95-100% of lambs and 70% in calves. Older animals may die acutely or develop an inapparent infection, sometimes abortion may be the only sign of the disease. In pregnant ewes, the mortality & abortion rates vary from 5 to almost 100% in different outbreaks. The rates in cattle are usually <10%. In humans, there is anorexia, fever, headache and muscular & joint pain. Death is rare but some may suffer vision impairment due to retinal hemorrhage. 07/08/2009 Dr. Ghalib's Lectures. Diagnosis The disease is suspected when abnormally heavy rains are followed by numerous abortions in pregnant ewes and high mortality rates among newborn animals showing lesions of necrotic hepatitis and influenza-like disease in peoples handling animals or their products. The Virus can be isolated from aborted fetus and blood of infected animals. It can be performed by intracerebral injection of mice or hamsters. The virus can also be isolated in baby hamster kidney or monkey kidney cell cultures. All serological tests can be used to detect antibody against RVF virus. Severe leukopenia is a common findings. Transmission tests to albino Swiss mice & sheep are also used. Dr. Ghalib's Lectures. 07/08/2009 Control Vectors control measures are not practical. In an enzootic area, immunization is the only effective way to protect livestock. Live attenuated vaccine is effective but it result in abortion of pregnant animals and congenital defects of the fetus. Pregnant ewes & cows should be vaccinated with killed formalin-inactivated vaccine. RVF outbreaks usually of sudden onset, so it is advisable to immunize lambs on regular basis of 6 mo of age. 07/08/2009 Dr. Ghalib's Lectures.
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