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 Re: Rift Valley Fever (Re: Elwaleed Ibrahim)
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Mortality Rates. Approximately 1% in humans. Rates are significantly higher in livestock. In addition, the fatality rate for fetuses in pregnant livestock is 100%, and the fatality rate for newborn lambs is 90%.
Treatment. Ribavirin, which is used to treat Lassa fever, has shown some promise as an antiviral. Other treatments also show promise, such as: interferon, immune modulators, and convalescent-phase plasma. However, the Egyptian strain of RVF appears to be not only more virulent, but also to be resistant to interferon. Currently, there is no specific treatment for the disease.
Outbreaks and History of Infection. Outbreaks are often associated with periods of heavy rainfall, after which the mosquito population flourishes. Outbreaks have been reported in Keyna, Sudan, Egypt, Cameroon, Central African Republic, Mali, Mauritania, Madagascar, Nigeria, Senegal, Somalia, South Africa, Tanzania, Zambia, and Zimbabwe. One of the earliest reported outbreaks occurred in 1950-1951 in Kenya, resulting in the death of 100,000 sheep. Imported European animals were especially susceptible to RVF.
The 1977 Egypt outbreak was thought to be caused by an unexplained spread from Sudan, possibly from the wind, imported camels or sheep, or by mosquitoes. The epizootic affected 25% to 50% of all sheep and cattle. Among humans, 200,000 fell ill, 18,000 clinical cases were confirmed, with 598 deaths from hemorrhagic fever. Human infection rates ran as high as 35%. Retrospective studies indicate that RVF was not present in Egypt before the 1977 outbreak.
In 1987, RVF broke out in Mauritania following the opening of Diama Dam at the mouth of the Senegal River, in an area where the virus was present but not generally recognized. The dam project created additional breeding grounds for mosquitoes carrying the disease, and resulted in more than 200 human deaths from RVF. The 1993 Egypt outbreak followed the opening of the Aswan dam. Other outbreaks, such as the 1997 outbreaks in Kenya and Somalia, have been associated with periods of heavy rain, when standing floodwaters become available as breeding grounds for the RVF mosquito vectors. The 1997 outbreak resulted in large losses of domestic animals, as well as more than 300 human deaths.
Some specific outbreaks:
- 1950-1951, Kenya
- 1967-1970, Nigeria
- 1969, Central African Republic
- 1976-1977, Sudan
- 1977-1978, Egypt
- 1987, Mauritania
- 1990-1991, Madagascar
- 1993, Egypt and Senegal
- 1997, Kenya and Somalia
In July, 1999, scientists reported that they have developed a strategy for predicting outbreaks (Science, July 16, 1999). Since heavy rains create conditions favorable to RVF vectors, scientists look at water temperatures in the Indian and Pacific Oceans to predict the heavy rains that, months later, affect East Africa and trigger the disease.
Vaccine. Killed RVFV vaccines and live-attenuated RVFV vaccines for animals (vetrinary use) are available, but they provide little protection for cattle, and they can cause birth defects and abortions in sheep. These vaccines are available as killed RVFV vaccines and as live-attenuated RVFV vaccines.
A human live attenuated vaccine, MP-12, is currently undergoing trials, but is not approved for human use. Other attenuated strains have been developed as potential live vaccines. Formalin-inactivated vaccines have been used to protect laboratory workers. A viral glycoprotein has also been developed.
pls see the following web site address
http://www.tarakharper.com/v_rift.htm#des
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