Abstract
Arthropod-borne encephalitis viruses are highly adapted to a particular reservoir host. Viruses spread from animal to animal by an infected specific mosquito or tick species. Mosquito or tick becomes infected when feeding on the viremic animal blood. Virus then replicates in the vector, ultimately infecting the salivary glands, which transmits the virus to a new host with infective saliva while taking a blood meal. Infected patients may become ill; they usually do not develop sufficient viremia to infect feeding vectors, and thus do not contribute to the transmission cycle. Among mosquito-borne encephalitis, the greatest public health threat in North America and is posed by the West Nile, St. Louis encephalitis, and La Crosse encephalitis viruses. Venezuelan equine encephalitis virus is of concern in Central and South America, while Japanese encephalitis virus affects residents or visitors to parts of Asia. Among the tick-borne encephalitis, tick-borne Encephalitis virus causes the greatest public health threat among residents or visitors to Eastern Europe and Asia. Eastern equine encephalitis (EEE) virus is widely distributed throughout North, Central, and South America and the Caribbean. EEE virus is the most severe one, with mortality up to 30% .Western equine encephalitis (WEE) virus is a found in North and South America and is a potential agent of bioterrorism through the aerosol route. Case fatality rate is 3 to 7%, .La Crosse virus (LAC) is the most pathogenic member of California encephalitis serogroup in central and eastern United States, mostly in school-aged children. Most infections are asymptomatic with low mortality rates. Treatment is supportive, with emphasis on control of cerebral edema and seizures. Murray Valley encephalitis (MVE) virus occurs in Australia, New Guinea, and probably islands in the eastern part of the Indonesian archipelago. MVE virus is maintained in a natural cycle involving water birds and Culex annulirostris. Only 1 in 1000 to 2000 infections had clinical illness; but, about one-third of patients die and about half the survivors suffered from neurologic deficits. Venezuelan equine encephalitis (VEE) widelyspread from Florida to South America, occur periodically, but occasionally, large epidemics occur among equine and humans. VEE is infectious via aerosols, making it an occupational risk to certain laboratory workers and a potential agent of bioterrorism. Effective prevention by immunizing equines, which serve as the primary amplification hosts for the epizootic VEE viruses. Tick-borne encephalitis (TBE) exists over a wide geographical area, including Russia and Europe. Human exposure occurs through work or recreational activities when the ticks are most active. TBE virus is transmitted from the saliva of an infected tick while taking blood meal. Case fatality rates range from 2 to 8%, Treatment is mainly supportive. In Middle Eastern Countries, no proper reported statistics, although the climatic environment favors the spreading of both the vectors and the viruses. So, it is advisable to make diagnostic techniques readily available and more public health awareness of those risky, potentially fatal infectious diseases. Already Dengue viral hemorrhagic fever is mostly responsible for major worldwide fatalities as well as West Nile Fever already present there from before, without specific treatment or vaccine available.
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