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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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Re: Rift Valley Fever Virus.............Haemorrhagic Fever (Re: ابن النخيل)
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RVF is an acute, febrile zoonotic disease caused by Rift Valley fever virus, which belongs to the family Bunyaviridae and genus Phlebovirus. The virus is primarily a vector-borne zoonotic pathogen. Humans acquire RVF through bites from infected mosquitoes or, more frequently, through exposure to the blood, body fluids, or tissues of animals that have been bitten by infected mosquitoes. Direct exposure to infected animals can occur during slaughter or through veterinary and obstetric procedures. RVF was first described in sheep in the early 20th century, and the virus was first isolated in humans in Kenya in 1930. In livestock, RVF causes abortion and death. Livestock epizootics can occur after heavy rainfall and flooding that result in hatching of Aedes mosquitoes (thought to be the initial vector and inter-epizootic reservoir of RVF) and other vectors that feed on nearby mammals.
Patients with RVF usually have initial signs and symptoms of influenza-like illness; less than 8% of patients subsequently have severe disease, including generalized hemorrhagic syndrome, encephalitis, or retinitis. The overall human mortality rate from RVF has been estimated at 0.5%--1.0% of those infected, but the rate is much higher among those with severe disease. The largest reported human outbreak occurred in Kenya during 1997--1998, in which an estimated 89,000 persons (based on a systematic serosurvey) were infected and 478 died; this outbreak also was centered in NEP. Previous RVF outbreaks among humans were not reported outside sub-Saharan Africa until 1977--1978, when approximately 18,000 persons became ill with RVF in Egypt, and in 2000, when approximately 800 persons in Saudi Arabia and 1,000 in Yemen had severe illness
Most of the cases before December 20 occurred in young men who herded livestock, perhaps because herdsmen are the first to identify and slaughter ill animals. Later in the outbreak, the distribution of cases broadened by age and sex. Young women also were overrepresented, perhaps because they handle uncooked animal products at home as they prepare meals for the family. Cases among children aged <5 years and the elderly have been rare, probably because they rarely interact with animals or handle raw animal products.
Most patients reported to KMOH had severe illness with bleeding, which likely accounts for the 29% case-fatality rate. Judging from previous studies, many mild, undetected RVF virus infections likely occurred during this outbreak. Additional cases of severe disease also might have occurred in NEP but were not detected because of the inaccessibility of many areas of the province resulting from flooding. Many areas of NEP, including an entire division of Garissa District, were unreachable by road from early December to mid-January.
Since mid-January, RVF in livestock has been detected in districts surrounding Nairobi, signaling occurrence of the outbreak in new areas. Reports also have been received of livestock and humans with illness consistent with RVF across the border in Somalia, where disease assessment has been hampered by ongoing security concerns. Several international organizations are collaborating to control the spread of the outbreak within Kenya and to other countries. Travelers should take precautions when visiting RVF-affected areas. Generally, the risk for RVF infection among travelers to Kenya is low, unless they visit areas where an outbreak is occurring and are bitten by infected mosquitoes or come in contact with body fluids, uncooked tissue, or aerosols from infected livestock. No preventive RVF medications or licensed vaccines for humans exist. Travelers to affected areas should reduce their risk for infection by protecting themselves from mosquito bites and by avoiding direct contact with livestock. Specific recommendations for U.S. travelers are available at
Timely detection of this outbreak was aided by implementation of Integrated Disease Surveillance and Response* within most of the affected districts. A second factor contributing to timely detection was initiation of RVF laboratory-supported field surveillance of febrile patients at outpatient clinics in Garissa. Ongoing epidemiologic, entomologic, and veterinary studies related to this outbreak continue to 1) identify factors associated with severe forms of RVF illness and poor outcomes; 2) characterize the role of specific species of mosquitoes in transmitting, maintaining, and spreading RVF virus; 3) assess the economic impact of the outbreak; and 4) define the impact of livestock immunization with live, attenuated RVF veterinary vaccine on minimizing the spread of animal and human disease. Taking measures to decrease contact with mosquitoes through use of repellents and bednets and avoiding exposure to blood or tissues of animals that might be infected are important protective measures for preventing RVF. Livestock vaccination also can be an effective means of preventing cases of human RVF if adequate vaccination coverage and herd immunity are achieved.
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ابن النخيل
فيس بوك
تويتر
انستقرام
يوتيوب
بنتيريست