Molecular biology of the Bunyaviridae.

More than 300 viruses, mostly arthropod-transmitted, are classified into the family Bunyaviridae, making it one of the largest groupings of animal viruses (Karabatsos, 1985). Until relatively recently these viruses were somewhat the 'Cinderellas' of animal virology, but with the increased recognition of their role in human diseases together with the results generated by the application of molecular techniques, the Bunyaviridae have achieved greater respectability. Rift Valley fever, CrimeanCongo haemorrhagic fever and California encephalitis viruses are serious human pathogens that are classified in the family Bunyaviridae. In the tropics febrile illnesses are often diagnosed under the 'great umbrella' (Downs, 1975) of malaria and treated as such; in fact many cases are probably caused by members of the Bunyaviridae, although true diagnosis is rarely achieved (Shope, 1985). Hantaan and related viruses, the causative agents of haemorrhagic fever with renal syndrome, are now recognized as belonging to the Bunyaviridae (Schmaljohn & Dalrymple, 1983) and cause a severe haemorrhagic disease with significant mortality throughout Asia, especially in China. As will be discussed later the Bunyaviridae have the capacity for sudden dramatic variation comparable to the antigenic shift associated with influenza viruses and thus warrant continual surveillance. At an academic level the Bunyaviridae display novel features in their gene coding arrangements and in their replication to maintain scientific interest. On a lighter note the Bunyaviridae also offer the opportunity to work with viruses having such glorious names as Main Drain, Pongola, Mahogany Hammock, Wongal etc. ; the reader is referred to the International Catalogue of Arboviruses (Karabatsos, 1985) for other gems. The criteria for inclusion in the family Bunyaviridae are the following: virus particles are spherical, 90-100 nm in diameter and enveloped with glycoprotein surface projections; the virions contain three unique segments of negative-sense single-stranded R N A in the form of