NSW Arbovirus Surveillance & Vector Monitoring Program
1999 - 2000 Annual Report

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EXECUTIVE OVERVIEW

      For the 1999-2000 season, the NSW Arbovirus Surveillance Program provided monitoring of mosquito vector populations and surveillance of arbovirus activity on the NSW western slopes and plains, coastal regions and metropolitan Sydney. The majority of sites operated between November and April. 

      The La Nia conditions that developed through 1998 continued into 1999, resulting in heavy rainfall in inland regions throughout the summer. Despite this, mosquito numbers were generally not extraordinary due to the cold temperatures across the state. However, Autumn was warm and this allowed mosquito numbers to remain high through to the end of the season. 

      The northwest of the state had extreme rainfall activity in late summer, leading to some very large mosquito collections, particularly at the new sites of Fords Bridge and Wanaaring. Floodwater Aedes mosquitoes dominated the collections and several viruses including RR and SIN were isolated from these mosquitoes. 

      There were 33 arbovirus isolates from mosquitoes, including 18 Ross River, 5 Sindbis and 10 unknowns. All of the isolates were from inland surveillance locations. 

      Several new mosquito species were recorded for the state, the most important of these was being a specimen similar in appearance to the exotic Japanese Encephalitis vector, Culex gelidus. 

       Sentinel chicken flocks were operated at Bourke, Condobolin, Deniliquin, Forbes, Griffith (2), Leeton, Menindee and Macquarie Marshes. Testing was extended into May for some flocks due to the Murray Valley Encephalitis virus (MVE) activity in central Australia. There were no flavivirus seroconversions for the season. 

      There was no MVE in NSW, despite one of the meteorological models suggesting possible activity. Due to the widespread activity in Western Australia, the Northern Territory and in the north of South Australia during 2000, and the fact that both the Forbes’ and Nicholls’ models are suggesting possible activity in 2000-2001, environmental conditions need to be closely monitored in the coming season. 

      The south coast continues to have dry conditions, with mosquito numbers well down. 

      The number of Sydney surveillance locations was reduced and overall mosquito numbers were relatively low. No viral isolates were made from the Sydney mosquitoes. There were occasional locally acquired cases of Ross River virus in Western Sydney, although not as many as previous years.  

      Human notifications for Ross River and Barmah Forest disease were down upon the previous season and below average. The only Area Health Service with more cases than the previous season was the Mid-North Coast.  

      The NSW Arbovirus Surveillance Web Site http://www.arbovirus.health.nsw.gov.au/ continues to expand and now has over 400 pages of information, with several new sections including climatic maps, press releases, mosquito information pamphlets, a teachers resource kit, and more photographs.

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