Classification, distribution and importance of arboviruses.

This essay reviews in concise form an extensive subject. Arborviruses belong to a number of different taxonomic groups, some of which include viruses not transmitted by arthropods. A state of the art definition of arboviruses is given which does recognise the importance of vertical transmission in arthropods to the basic maintenance of some arboviruses. Most of the arboviruses which affect humans are included in the families Togaviridae, Flaviviridae, Bunyaviridae, Reoviridae and Rhabdoviridae. Many arbovirus infections are symptomless. Clinical manifestations range from mild febrile illness, which may or may not be accompanied by skin rash and by arthralgia, to severe and often fatal encephalitis or haemorrhagic fever with shock. Three arboviral diseases considered at present as the most important ones are discussed in more detail: dengue and dengue haemorrhagic fever (DHF), yellow fever and Japanese encephalitis (JE). They have caused some of the most devastating epidemics in recent years. DHF has developed into a major paediatric problem in South East Asia and the Western Pacific with over 6,000,000 hospital admissions and 20,000 deaths in the two regions over the last 20 years. Spectacular outbreaks of yellow fever, such as the one in Ethiopia in 1960-1962 with 15,000-30,000 estimated deaths, still occur in Africa in areas contiguous to rain forest regions where jungle yellow fever is enzootic. JE is characterized by significant mortality in children and old people in many countries of Asia, where the epidemiological patterns and the distribution of the disease have changed in recent years. The complex interrelated factors which are involved in arbovirus ecology are illustrated.(ABSTRACT TRUNCATED AT 250 WORDS)