NSW Arbovirus Surveillance & Vector Monitoring Program
2001 - 2002 Annual Report

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EXECUTIVE OVERVIEW

      For the 2001-2002 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, south coast 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. 

      Rainfall was well below average through the late spring and early summer months and this, coupled with temperatures which were also well below average, ensured that mosquito numbers remained lower than normal across the inland for the entire season.

      With the low mosquito numbers, there was minimal virus activity, with only 25 isolates from inland collected mosquitoes, including 1 Ross River, 1 Edge Hill, and 23 unknowns. As a result of the low mosquito/arbovirus activity, the total number of human notifications from inland regions was one of the lowest since reporting began.

      Despite the detection of Murray Valley Encephalitis (MVE) in the 2000-2001 season, along with intensive and widespread Kunjin activity, there was no evidence of either virus in the sentinel chicken flocks or from the virus isolations from the mosquitoes in 2001-2002.  

      Neither the Forbes’ or Nicholls’ models are suggesting probable MVE activity for the 2002-2003 season.

      Only six coastal locations undertook trapping this year. Coastal rainfall patterns were below average in early summer and mosquito numbers were also down. Heavy rainfall coupled with high tides lead to large collections in February of the saltmarsh mosquito Ochlerotatus vigilax but freshwater species, including Culex annulirostris and Coquillettidia linealis, were also highly abundant.

      Three isolates of Ross River virus were made from only 105 Ochlerotatus vigilax trapped at Batemans Bay in mid-February. Fortunately, this very high virus carriage rate occurred when overall mosquito numbers were well down upon normal and thus human notifications remained low within the region.

      Early 2001 saw the largest epidemic of Barmah Forest virus in Australia to date being centred within the Mid-North Coast AHS. Barmah Forest virus activity again extended into the 2001-2002 season, with numbers of patients only slightly below the previous year. This season, the Barmah Forest epidemic extended into the Hunter region with the number of patients up by over 700%. The Central Coast also experienced higher than average cases. Ross River notifications were well down and the Mid-North Coast AHS continued to have the highest number (and rate) of total arbovirus notifications for NSW.

      There was some Barmah Forest activity in western Sydney, with several mosquito isolates, including the first for Australia from the domestic species, Ochlerotatus notoscriptus. There were also some human notifications from within the region. Generally, mosquito numbers from Sydney were not extraordinary.

      The NSW Arbovirus Surveillance Web Site http://www.arbovirus.health.nsw.gov.au continues to expand and now has over 120MB of information with 560 pages.

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