Birnaviridae

Birnaviruses are medium-sized unenveloped icosahedrons containing a biseg-mented dsRNA genome. The family Birnaviridae was officially established by the International Committee on Taxonomy of Viruses in 1984. The prototype of birnaviruses is infectious pancreatic necrosis virus (IPNV), which can cause high mortality epizootics in young salmonid fish. Another member is infectious bursal disease virus (IBDV) of chickens, which infects the lymphoid cells of the bursa of Fabricius of domestic fowl, resulting in humoral immunosuppression. The only insect birnavirus is Drosophila X virus (DXV), which causes anoxia sensitivity and death of infected fruit flies. It appeared in France in 1979 as a contaminant in Drosophila melanogaster in a laboratory where the replication of sigma virus (an insect rhabdovirus) was being investigated. DXV-infected flies died after a 15 min exposure to pure C02 or N2, whereas uninfected flies did not exhibit similar sensitivity.