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 Rift Valley Fever Virus.............Haemorrhagic Fever
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Rift Valley fever (RVF) virus, family Bunyaviridae, genus Phlebovirus, is a mosquito-borne pathogen capable of causing explosive outbreaks of severe human and livestock disease throughout Africa and more recently in 2000 on the Arabian peninsula. RVF virus infections in humans are characterized by a mild self-limiting febrile illness that can in a small percentage (ca. 1 to 2%) of patients progress to more severe complications including hepatitis, delayed onset neurologic disease, retinitis, or a hemorrhagic syndrome with high mortality. Economically disastrous livestock epizootics often precede the detection of human illness and have been recorded since the early 1900s. Livestock epizootics usually manifest as sweeping "abortion storms" and high newborn mortality approaching 100% among sheep, goats, and cattle.
Although low-level RVF activity most likely occurs throughout enzootic regions each year, the emergence of RVF virus in large epidemic and/or epizootic cycles is typically associated with unusually heavy rainfall and the emergence of the natural reservoir host, which is thought to be primarily transovarially infected Aedes spp., floodwater mosquitoes. During large epidemics and epizootics the high numbers of infected individuals can greatly strain the capacity of the public health and veterinary infrastructure to provide rapid real-time diagnostic testing and basic medical care for infected individuals or animals.
The ability of RVF virus to cross international and natural boundaries is well documented. In 1979 RVF virus was identified for the first time outside of continental Africa on the island of Madagascar. In addition, on at least two separate occasions the virus has caused "virgin soil" outbreaks in previously unaffected countries. In 1977 RVF virus was recorded for the first time north of the Sahara desert in Egypt and resulted in a massive epizootic/epidemic during which greater than 200,000 people were estimated to have been infected. Later in 2000, the virus was isolated for the first time outside of Africa across the Red Sea in Saudi Arabia and Yemen. The potential of further introductions of RVF virus into previously unaffected countries via infected livestock importation, mosquito translocation, or human travel or through intentional release illustrate the need for safe and effective veterinary and human vaccines and broadly based pan-RVF virus real-time molecular diagnostic assays.
The tripartite negative-sense single-stranded RNA genome of RVF virus contains the small ambisense segment (S segment) encoding the nucleoprotein and the nonstructural proteins, the medium segment (M segment) encoding the polyglycoprotein precursors, and the large segment (L segment) containing the virus RNA-dependent RNA polymerase. Recent complete genome sequencing of multiple isolates of RVF virus revealed that the overall virus genomic diversity is low (5%) at the nucleotide level. This previous work involved the complete genomic characterization of the S, M, and L segments of 33 wild-type virus isolates collected from throughout Africa and Saudi Arabia spanning 56 years (1944 to 2000).
(عدل بواسطة ابن النخيل on 11-13-2007, 11:16 PM)
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ابن النخيل
فيس بوك
تويتر
انستقرام
يوتيوب
بنتيريست