Summary
Arboviruses are a heterogeneous group of viruses transmitted by a hematophagous arthropod vector. The most well known and most serious disease caused by an arbovirus is yellow fever. Arboviruses belong to the following families: togaviridae (equine encephalitis, Chikungunya virus; see these terms), flaviviridae (dengue, yellow fever, St Louis encephalitis, West Nile encephalitis; see these terms), bunyaviridae (California encephalitis, Bunyaviral hemorrhagic fever; see these terms). Ticks, sandflies or mosquitoes are their vectors. Arboviruses predominate in tropical countries. They all show tropism towards small vessels and the central nervous system. Arboviruses are polymorphic diseases typically evoked by encephalitis and hemorrhage, however most commonly only aspecific fever is observed. The incubation period is 7-10 days, after which onset is brutal, with high fever, cephalalgia, aches, and general malaise that lasts 2 or 3 days. The disease can then either heal spontaneously or progress to a clinical presentation that is specific to each virus. Classical dengue fever and related syndromes are characterized by macular rash, polyadenopathy, and minor hemorrhage, after which the symptoms resolve spontaneously. Hemorrhagic dengue is complicated by significant hemorrhage and a mortality rate that ranges from 10-20% (South East Asia and the Caribbean). Encephalitis varies between mild, with uncomplicated meningitis, and severe. Arboviruses that cause encephalitis have been classified in 4 groups: American equine encephalitis, Japanese encephalitis complex, encephalitis caused by ticks, and California encephalitis. Yellow fever is caused by the amarillic or yellow fever virus and progresses in 2 phases: a red congestive phase with diffuse erythema and conjunctival hyperemia, followed by the yellow phase with hepatocellular failure. Mortality remains high. There are no effective drugs for this virus, however an antiamarillic vaccine gives protection against the virus for 10 years. This vaccine is essential to the prevention of this dreadful disease and its use is regulated by international law. Studies are currently under way to adjust a vaccine for West Nile virus because no antiviral has proved effective in vitro. *Author: Dr E. Aslangul (August 2006)*.
