INTRODUCTION

Bunyaviruses comprise the largest family of arthropod-transmitted viruses. Of the 300 or so viruses in the family Bunyaviridae more than half are transmitted by mosquitoes (Calisher, 1996). A number of these viruses cause disease in man or animals, although thus far many have not been associated with human illness. The family is classified into five genera, Orthobunyavirus, Hantavirus, Nairovirus, Phlebovirus and Tospovirus, and each genus is associated with a principal arthropod vector, except the hantaviruses, which have no arthropod involvement in their life cycle. Tospoviruses are transmitted by thrips to plants, nairoviruses primarily by ticks, and orthobunyaviruses predominantly by mosquitoes. The Phlebovirus genus contains viruses transmitted by phlebotomine flies, ticks and, notably for Rift Valley fever virus, mosquitoes as well. This chapter will deal with the interactions between orthobunyaviruses and mosquitoes.

BUNYAVIRUS CHARACTERISTICS

All bunyaviruses have a tri-segmented single-stranded RNA genome of negative-sense (or a variant of negative-sense, termed ambisense) polarity. The genomic RNA segments are called L (large), M (medium) and S (small). All family members encode four structural proteins – two glycoproteins called Gn and Gc according to their position within the primary gene product, a nucleoprotein, N, that encapsidates the genomic (and antigenomic) RNA segments and an RNA-dependent RNA polymerase, called L protein. The pattern of sizes of the viral proteins and the RNAs is conserved within a genus (Elliott et al., 2000). Viruses in some genera also encode non-structural proteins on their M and/or S RNA segments, termed NSm and NSs, respectively.