Rift Valley Fever [Archives:2000/41/Health]

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October 9 2000

Dr. Vet. Mohammad Mustafa Murad
Definition:
Rift Valley Fever (RVF) is a viral disease of sheep-goats-cattle-camels and other ruminant.. etc. characterized by fever, a high mortality in lambs, kids and small calves as well as abortion of pregnant ewes, goats, and cows; also characterized by a necrotic hepatitis. Man is susceptible to disease so that RVF is an enzootic disease.
RVF first broke out in Rift Valley in Kenya in 1931, in south Africa in 1975 and in Egypt at 1977. It is also appearing in other countries like Sudan, Somalia and Mauritania. Now at 2000 an outbreak of the disease has occurred in Saudi Arabia and in Yemen.

Cause
RVF is caused by a virus related to Bunyaviridae group (Arbovirus).

Transmission:
RVF is transmitted by Culicric mosquito and other various species of mosquitoes; also by direct contact with infected materials (dead fetus, blood, spleen, liver and other tissues of diseased animals). The disease is not transmitted by indirect contact.

Incubation Period
The incubation period is very short; it is (12-24) hours in lambs, kids and very small calves, and (24-96) hours in sheep, goats, and cattle, and (4-6) days in man.

Symptoms
The disease runs an extremely rapid course.
In lambs, and kids, the disease is as peracute form and the symptoms – if seen – are that a high temperature reaches 24C, in appetence, staggering gait and diarrhea followed by rapid death.
In sheep, goats and cattle, the disease occurs in an acute form and the symptoms are fever with temperature raising to 41C, tistless, anorexia, unsteady gait, nasal discharge, some times purulent, reduction in milk, diarrhea and progressively weakness inlachation animals.
The pregnant ewes and cattle abort at any stage of gestation period.
The symptom of infected men are influenza like character and eye complication, ..etc.

Mortality Rate
In new and small lambs, kids and calves, the mortality rate is very high between 90 – 95%.
In adult sheep, goats the mortality rate reaches 20-30%.
In adult and older cattle, the percent of death is about 10%.
In man, the fatality rate is very low and less than 1.5%, but in very severe infection, the percent may reach about 10% due to complication problems.

Diagnosis by:
History of the outbreak.
Short incubation period in all infected animals.
High percent of death in young lamb and kids.
Abortion in pregnant ewes, goats and cattle.
Necrosis of the liver if post-mortem examination is done.
Infection of man by being bitten by infected mosquitoes, or by direct contact with infected materials.

A positive diagnosis is done by the laboratory examination for isolation of the virus or detection of antigen or histopathology to liver slices or by serological tests.

Control and Prophylaxis
The most important step of control the disease is by eradication the mosquitoes and using good insecticide for spraying periodically by different methods.
Annual vaccination of the animal by attenuated virus vaccine or dead virus vaccine, but the pregnant animals should not be vaccinated because it is dangerous to the featus and abortion immunity.
Applying the veterinary quarantines :
a) Prevention of the importation of living animals and animal products from the countries where the RVF disease is known as occur.
b) Prevent the transportation of the animals from the infected area to any other area.
c) Isolation of the very diseased animals, and burial in the ground as soon as possible.
d) Carcasses of dead animals should be always buried in the ground or burned.
Hyper immune serum is available and it is useful to animals.
Veterinarians working in the field and laboratory, can be protected by vaccination with formalin inactivated virus vaccine.

Immunity
Vaccinated animals take immunity for about one year
Animals recovered from diseased take permanent immunity (lifelong). Passive immunity occurs after ingestion of colostrum (first mild of location period) from immune ewes and that immunity persists for about 5 months.
Poultry and pigeons have natural immunity; i.e. they are not taking infection by RVF disease.

Treatment
No specific treatment is available to animal and man.

Ex-consultant at the Ministry of Agriculture and Irrigation and Ex-consultant at the Animal Wealth of the Social Fund for Development

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