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==Control==
==Control==
Modified live and inactivated '''[[vaccines]]''' are available. Live vaccination is only recommended in '''non-pregnant''' animals due to its ability to cause abortion and neurological deficits in lambs. In epizootic situations though, this risk may well be worth taking.
Herd monitoring has been used extensively in Africa as a means of building up a picture of disease spread as well as to identify risk areas. Sentinel herds in representative areas are used for monitoring. Blood is collected initially and, providing no seropositivity is detected, animals are sampled at the beginning of the rainy season and every four to six weeks up to the end of the rainy season. This allows the early detection of any epidemics. Monitoring is also important as RVF outbreaks in animals precede outbreaks in human populations, as well as identifying increases in vector numbers.
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During an outbreak, control at slaughterhouses to reduce zoonotic spread. Contact with animals, both direct and indirect, should be avoided. Movement restrictions should be enforced to prevent movement of the disease from diseased areas to RVF free areas; however movement restrictions within endemic countries have had little impact on the spread of RVF.
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Forecasting is key as outbreaks occur following a period of heavy rain, thus is rain is forecast preventative measures can be implemented beforehand to help prevent/ lessen the impact of an outbreak.
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Mosquito breeding sites should be reduced through drainage and larvicidal measures. Methoprene spraying, larvicidal toxins and controlled burning can be used, though low level aerial spraying has been shown to have little effect.
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Education of risk factors and mosquito bite prevention, appropriate clothing, use of insect repellent and mosquito nets should be undertaken. Local populations should be educated as to the risks of eating raw meat and milk products (though a fall in pH destroys the virus so some uncooked meat may be safe).
===Vaccination===
Modified live attenuated and inactivated virus vaccines are available.
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The live attenuated '''Smithburn''' vaccine only requires one dose but may cause spontaneous abortion in pregnant stock. This vaccine has adverse effects in newborn kids and lambs and teratogenic effects or abortion in pregnant cows, ewes and goats. Protection is conferred to offspring via suckling. Antibody titres post vaccination are higher in sheep than cattle. One dose will protect for three years.
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The formalin inactivated virus vaccine (with Aluminium Hydroxide adjuvant) requires multiple doses to achieve immunity, and annual boosters are needed as it is less immunogenic. It is safe to use in pregnant ewes. Biosecurity is also a consideration when using this vaccine as reversion to virulence is a possibility.
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Vaccines should be administered prior to outbreak to prevent an epizootic. Vaccination during an outbreak may worsen the situation, especially if multi dose vials are used, due to the possibility of viraemic animals being vaccinated and then the same vial being used on a healthy animal, thus spreading the virus. The use of the Smithburn vaccine is restricted in non endemic areas and during outbreaks due to the possibility of reassortment and a return to virulence.
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More recently a naturally attenuated virus vaccine has been developed (Clone 13) that is marketed in South Africa and Namibia. Testing in pregnant ewes and lambs demonstrated safety and it has been shown to be as effective as the Smithburn vaccine in conferring immunity. The vaccine has however shown to cause neurological disease and paralysis in some vaccinated mice.
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A live attenuated vaccine MP12 has been shown to be safe in newborns, lambs and pregnant cows and ewes. Malformation has occurred when the vaccine was administered to sheep during the first trimester (days 35-56) and viral shedding has been documented in macaques following MP12 vaccination. Colostrum from vaccinated ewes gives temporary immunity to lambs.
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An R566 strain has been developed from MP12 and Clone 13 and has shown to confer immunity in laboratory experiments.
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Viral vector vaccines using sheep pox and lumpy skin disease viruses have been shown to give protection, and have the advantage that the diseases exist in the same habitats and could potentially confer protection to two diseases with one vaccination but the use is restricted to countries with sheep pox and lumpy skin disease due to the use of the vectors. A vaccine using Newcastle disease virus as a vector has also been developed.
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A recombinant virus vaccine has been found to be safe and effective in pregnant and non pregnant ewes, even when challenged with the virus. This vaccine has the advantage that it would allow differentiation between vaccinated and previously infected animals using a DIVA ELISA test (as would vector vaccines)
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DNA and virus particle based vaccines are currently being developed and have demonstrated some level of protection against RVF virus. Plant derived subunit vaccines are also being researched.
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Vaccine storage and transport is an issue within developing countries; breaking of the cold chain may result in ineffective vaccines being administered. However, a study has shown that the use of a formalin inactivated vaccine transported 200km at ambient temperatures had no adverse effect on antibody responses.
|flashcards = [[Rift Valley Fever Flashcards]]
|flashcards = [[Rift Valley Fever Flashcards]]
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==References==
==References==