In 1995, the largest recorded outbreak of human disease resulting from infection with the mosquito transmitted alphavirus Barmah Forest (BF) virus occurred along the south coast of New South Wales, Australia. The virus was first isolated in early January from mosquitoes collected at Batemans Bay and predisposed the recognition of 135 human clinical cases. The cases of BF virus were identified initially from Batemans Bay during late January, and the majority (30%) of all cases came from this town. After 5 wk, all major centers on the south coast had clinical patients. Aedes vigilax (Skuse) were especially abundant at Batemans Bay, with levels up to 8 times greater than normal. This species yielded 111 isolates and appeared to be the major vector of BF virus. Attempts to examine if BF virus was maintained in the field by vertical transmission within Ae. vigilax populations were unsuccessful; no evidence of vertical transmission with BF virus, nor any other arbovirus, was found in > 17,000 adults emerging from field-collected larvae from the region following peak virus activity. In addition to BF virus, other viruses were recovered from field-collected adult mosquitoes, including Ross River (10 isolates), Edge Hill (21), and Stratford (10). Ae. vigilax again yielded the majority of these viral isolates. The BF virus outbreak appeared to be associated with several factors. A lack of recent BF virus activity in the region provided a highly susceptible human population, and unusual weather conditions of above average rainfall coupled with high tides resulted in extraordinarily large populations of Ae. vigilax.

There are many gaps to be filled in our understanding of mosquito-borne viruses, their relationships with vectors and reservoir hosts, and the environmental drivers of seasonal activity. Stratford virus (STRV) belongs to the genus Flavivirus and has been isolated from mosquitoes and infected humans in Australia but little is known of its vector and reservoir host associations. A total of 43 isolates of STRV from mosquitoes collected in New South Wales between 1995 and 2013 was examined to determine the genetic diversity between virus isolates and their relationship with mosquito species. The virus was isolated from six mosquito species; Aedes aculeatus, Aedes alternans, Aedes notoscriptus, Aedes procax, Aedes vigilax, and Anopheles annulipes. While there were distinct differences in temporal and spatial activity of STRV, with peaks of activity in 2006, 2010 and 2013, a sequence homology of 95.9%–98.4% was found between isolates and the 1961 STRV prototype with 96.2%–100% identified among isolates. Temporal differences but no apparent nucleotide divergence by mosquito species or geographic location was evident. The result suggests the virus is geographically widespread in NSW (albeit only from coastal regions) and increased local STRV activity is likely to be driven by reservoir host factors and local environmental conditions influencing vector abundance. While STRV may not currently be associated with major outbreaks of human disease, with the potential for urbanisation and climate change to increase mosquito-borne disease risks, and the possibility of genomic changes which could produce pathogenic strains, understanding the drivers of STRV activity may assist the development of strategic response to public health risks posed by zoonotic flaviviruses in Australia.

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Wyeomyia (Wyeomyia) mitchellii (Theobald) (Diptera: Culicidae) was recovered for the first time on Guam, United States of America, in 2017. Larval specimens were collected from water-filled axils of bromeliads during a larval survey carried out in a residential neighborhood of the Chalan Pago/Ordot area. Native to the New World, Wy. mitchellii has likely made its way to the Pacific Islands through the possibly illegal import of ornamental bromeliads. While this mosquito does not represent a significant threat to public health, this finding highlights the vulnerability of the Pacific Islands to the introduction of exotic species, including mosquito species that may increase public health risks.