NSW Annual report 2000-2001

NSW Arbovirus Surveillance & Vector Monitoring Program

2000 - 2001 Annual Report

WEATHER DATA

MOSQUITO MONITORING
     Methods
   Results
         Inland
         Coastal
         Sydney
ARBOVIRUS ISOLATIONS
     Methods
   Results
         Inland

EXECUTIVE OVERVIEW

For the 2000-2001 season, the NSW Arbovirus Surveillance Program: (i) Monitored mosquito vector populations and undertook surveillance of arbovirus activity on the NSW western slopes and plains, far north coast region and metropolitan Sydney. (ii) Monitored flavivirus transmission through the testing of sentinel chickens across inland NSW. The majority of sites operated between November and April.

The inland experienced widespread heavy rainfall in October and November 2000. This followed heavy rains in the north of the state during early 2000. Inland mosquito numbers were well above average across the state early this season, but declined and remained below normal following hot and dry January conditions.
For the first time since 1974, Murray Valley Encephalitis (MVE) virus was detected in NSW, with seroconversions in the sentinel chicken flocks at Bourke, Macquarie Marshes, Menindee and Wanaaring. The virus appeared not to reach southern NSW, possibly due to the below average mosquito numbers with the lower rainfall. In response to this activity, two new flocks were established, the bleeding season was extended to the end of May, and opportunistic testing of chickens was undertaken in the northeastern inland. There were no human cases of MVE reported in NSW, although cases occurred in Qld, NT and WA.

Serological confirmation of a case of MVE infection in a tourist who presented with severe encephalitis after return to Europe was undertaken at the ICPMR.

Both the Forbes’ and Nicholls’ models are again suggesting MVE activity for the 2001-2002 season. The prospect of the virus over-wintering cannot be excluded and it is recommended that surveillance measures be enhanced for the next season.

There was extensive KUN activity throughout the state starting in Menindee with the first sentinel chicken seroconversion on 18/1/01. Further seroconversions occurred at Bourke, Deniliquin, Fords Bridge, Griffith, Lake Cargelligo, Leeton, Macquarie Marshes, and Wanaaring. There were also mosquito isolates of KUN from 12/2/01 at Leeton, which indicated the start of the activity in southern NSW.

The largest epidemic of Barmah Forest virus in Australia to date occurred, with at least 307 human cases for the season from the north coast, and the majority from April to June 2001. This outbreak was centred on the Kempsey area and followed upon record rainfall levels leading to extensive flooding. The Mid-North Coast AHS again had the highest number of arbovirus notifications for any area health service.

There were 44 arbovirus isolates from mosquitoes, including 6 Ross River, 23 Sindbis, 2 Kunjin, 1 Kokobera and 12 unknowns. All but one was from the inland.

The number of coastal trapping locations was further reduced to five, with no monitoring from the south or lower north coast (including where BF virus activity was present). Mosquito numbers peaked in late February and again in April following rain combined with high tides. The Sydney sites showed a similar trend with large collections at Penrith, particularly of Culex annulirostris. Several locally acquired cases of human RR virus occurred around Penrith, and are being investigated.

The NSW Arbovirus Surveillance Web Site http://www.arbovirus.health.nsw.gov.au/ continues to expand and now has over 560 pages. The most significant new feature is a search engine, enabling required information to be quickly retrieved.