The family Bunyaviridae comprises over 200 viruses (serotypes, subtypes, and varieties) that infect vertebrates and/or invertebrates. Four genera of viruses have been defined (Bunyavirus, Nairovirus, Phlebovirus, and Uukuvirus). The main characteristics of the member viruses are: (i) the virus particles are for the most part uniformly spherical, 80–110 nm in diameter, and possess a unit membrane envelope from which protrude polypeptide spikes 5–10 nm long; (ii) the viruses have three helical nucleocapsids, often in the form of supercoiled circles, each consisting of a single species of single-stranded RNA, a major nucleocapsid polypeptide, N, and at least in some cases minor amounts of a large polypeptide which may be a transcriptase component; (iii) the genome is composed of three species of RNA (L, large; M, medium; and S, small), organized in end-hydrogen bonded circular structures; (iv) most viruses have three major virion polypeptides (N, and two surface polypeptides, designated Gl and G2); (v) for at least some member viruses, the virions have been shown to contain an RNA-directed RNA polymerase, believed to be responsible for the synthesis of viral complementary mRNA, so that bunyaviruses are considered to be negative-stranded viruses; (vi) at least some bunyaviruses are capable of heterologous virus genome segment reassortment and can form recombinant viruses at high or low frequency; (vii) viruses appear to mature primarily at smooth membrane surfaces and accumulate in Golgi vesicles and saccules, or nearby; (viii) transovarial, venereal and/or transstadial transmission in arthropods has been shown to occur for some members of the family.

Eight monoclonal antibodies (MAbs) derived using yellow fever (YF) virus (French viscerotropic virus strain) labelled the nuclei (wild-type strains) and/or the nucleoli (vaccine strains) of cells infected with different strains of YF virus. The specificity of these antibodies for YF virus-infected cells was confirmed using MAbs that bind only the YF virus envelope glycoprotein. The characteristics of fluorescent labelling in the nuclei and nucleoli of both normal cells and of nuclei separate from cell cytoplasm confirmed that the antigen was inside the nucleus rather than on the outer surface of the nuclear membrane. Virus-specific antigen was also observed in the cytoplasm of infected cells. One additional virus envelope-specific antibody, derived at the same time, identified cytoplasmic antigen exclusively. The eight antibodies that identified nuclear antigen showed no activity in neutralization, haemagglutination inhibition or mouse protection tests. Analysis of their molecular specificities by radioimmunoprecipitation of virus-infected cell lysates showed that they identified the non-structural NS5 antigen of YF virus. These results support the possibility of nuclear involvement in the replicative stages of YF virus infection.

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A new genus, bunyavirus, is proposed. As it cannot be allocated to a currently existing family, the establishment of a new one, Bunyaviridae, is suggested.

flavivirus pathogenesis has not been satisfactorily assessed. This review examines the antigenic interrelationships of the flaviviruses, considers some of the implications of antigenic cross reactivity in virus virulence and highlights potential consequences of virus-antibody interactions.