The Bunyaviridae family contains more than 300 viruses, mostly transmitted by arthropods. Spherical particles measuring 80–120 nm contain a single-stranded, negative-sense or ambisense, triple-segmented RNA genome 11–19 kb in total size. The envelope has two glycoproteins. Several member viruses produce mosquito-borne encephalitides of humans and animals; others cause hemorrhagic fevers. Transovarial transmission occurs in some mosquitoes. Some are trans mitted by sandflies. HPS is caused by a virus transmitted by rodents. Bunyaviruses are sensitive to inactivation by heat, detergents, formaldehyde, and low pH; some are hemaggluti nating (see Figure 1).

Fig1. Electron micrographs of typical arboviruses and rodent-borne viruses. A: An alphavirus, Semliki Forest virus (Togaviridae). B: A representative member of Bunyaviridae, Uukuniemi virus. C: An arenavirus, Tacaribe virus (Arenaviridae). D: Ebola virus (Filoviridae). (Courtesy of FA Murphy and EL Palmer.)

The California encephalitis virus complex comprises 14 antigenically related viruses in the Orthobunyavirus genus of the family. This includes La Crosse virus, a significant human pathogen in the United States (see Table 1). La Crosse virus is a major cause of encephalitis and aseptic meningitis in children, particularly in the upper Midwest. Most cases occur between July and September in children younger than the age of 16 years. There are about 80–100 cases of La Crosse encephalitis reported per year.

Table1. Summary of Major Human Arbovirus and Rodent-Borne Virus Infections That Occur in the United States

The viruses are transmitted by various woodland mosquitoes, primarily Aedes triseriatus. Principal vertebrate hosts are small mammals such as squirrels, chipmunks, and rabbits. Human infection is tangential. Overwintering can occur in eggs of the mosquito vector. The virus is transmitted transovarially, and adult mosquitoes that develop from infected eggs can transmit the virus by bite.

The onset of California encephalitis viral infection is abrupt, typically with severe headache, fever, and in some cases vomiting and convulsions. About half of patients develop seizures, and the case-fatality rate is about 1%. Less frequently, patients have only aseptic meningitis. The illness lasts from 10 to 14 days, although convalescence may be pro longed. Neurologic sequelae are rare. There are many infec tions for every case of encephalitis. Serologic confirmation by HI, ELISA, or neutralization tests is done on acute and convalescent specimens.

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مواضيع ذات صلة

Pathogenesis of SARS-CoV-2 and COVID-19

Viral Serology :General Principles

Virus detection methods: Cell Culture

Virus detection methods: Molecular Detection Using Nucleic Acid Probes and Polymerase Chain Reaction Assays

Virus detection methods: Immunodiagnosis (Antigen Detection)

Arenavirus diseases

Bunyavirus diseases

Dengue Virus

Clinical Features of Yellow fever

Virus detection methods: Electron Microscopy

Virus detection methods: Cytology and Histology

Specimen Transport and Storage in viral infections