Barmah Forest virus (BFV)

see also:

• zoonoses
• Ross River virus (RRV)
• Murray Valley encephalitis (MVE)
• Japanese encephalitis virus (JEV)
• https://www.health.vic.gov.au/infectious-diseases/barmah-forest-virus-disease

• a mosquito-borne viral infection which causes epidemic polyarthritis with very similar clinical features to Ross River virus (RRV)
• a member of the alphavirus genus of viruses which also includes Ross River, Sindbis and Chikungunya virus
• first isolated in 1974 from Culex annulirostris mosquitoes collected in the Barmah Forest near the Murray River in northern Victoria, and simultaneously from mosquitoes collected in south-west Queensland.
• mosquitoes carrying this arbovirus live around coastal salt marshes, and may be the same species that carries Ross River virus
• no evidence of transmission from person to person as it requires an insect vector for transmission
• infection with BFV confers lifelong immunity

• inland areas: Culex annulirostris same as for Ross River virus (RRV)
• coastal salt marsh regions: Ochlerotatus vigilax (New South Wales) and Ochlerotatus camptorhynchus (Victoria) same as for Ross River virus (RRV)
• Northern Territory: the midge Culicoides marksi

female Ochlerotatus camptorhynchus image courtesy of Tasmanian insect field guide

Culex annulirostris image courtesy https://wrbu.si.edu/vectorspecies/mosquitoes/annulirostris

• it is likely, that macropods and other marsupials are the principal hosts for the virus
• antibodies have been found in kangaroos, cattle, horses and sheep

• prevalence is 1/100th that of Ross River virus (RRV) infections with annual notifications in Victoria averaging around 6 per year (compared to 100-2000 per year for Ross River virus (RRV))
• it is considered endemic throughout regional Victoria, especially near Echuca, but may be found throughout Australia
• Feb-March 2019 5 cases occurred south of St Helens, Tasmania's east coast ¹⁾

• usually 7-10 days but can range from 3 to 21 days

• most cases are subclinical and clinical disease is rare in pre-pubertal children
• features include fever, arthralgia and rash that are clinically indistinguishable from those caused by Ross River virus disease which may occur concurrently
• recovery usually occurs within several weeks, but lethargy, arthralgia and myalgia can persist for over 6 months

• serology:
  • IgG seroconversion or a significant increase in antibody level or a fourfold or greater rise in titre to BFV
  • detection of BFV-specific IgM in the presence of BFV IgG
• detection of BFV by nucleic acid testing

• supportive care, rest, analgesia, anti-inflammatory agents