NSW Arbovirus Surveillance & Vector Monitoring Program

2000 - 2001 Annual Report

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SENTINEL CHICKEN FLOCK PROGRAM

A major review of the locations of the sentinel chicken flocks was undertaken in mid-2000, with the aim of ensuring that the flocks were situated in a scientifically appropriate site, i.e. in an area with high mosquito contact and numerous water birds, and where there may be zoonotic virus activity (i.e. potential virus ‘hotspots’). Another objective was to establish more flocks in the northwest of the state. One theory is that MVE enters NSW from the northwest of the country with dispersing waterbirds following unusually heavy rainfall activity. If this is the case, sites in the northwest may be expected to detect MVE before it reaches the more populated areas in the south.

This review led to several changes including the deletion of the Condobolin flock, the reestablishment of a flock at Lake Cargelligo, new flocks at Fords Bridge and Wanaaring, and the relocation of the flocks at Bourke, Griffith, and Macquarie Marshes to more appropriate sites. Sentinel chicken flocks of 15 birds were initially deployed at ten locations this season including Deniliquin, Forbes, Leeton and Menindee, in addition to the abovementioned sites. Regular testing started in November and the birds were bled weekly and tested for the presence of flavivirus antibody. If birds seroconverted to a flavivirus, additional tests were performed to determine whether the infection was due to MVE or KUN. Results were emailed and faxed to the public health units, and included on the NSW Arbovirus Surveillance web site.

For the first time, since sentinel chicken flocks were deployed, there was evidence of MVE activity in NSW, with seroconversions in the sentinel flocks at Bourke, Macquarie Marshes, Menindee and Wanaaring. In all but Macquarie Marshes, the MVE activity was short-lived, with seroconversions occurring in a single week (albeit different weeks for each location). Concomitant with the MVE was widespread KUN activity, with seroconversions in both the northern and southern flocks, and all of the original ten locations except Forbes showed activity.

Table 2 summarises the seroconversions across NSW for the 2000-2001 season. Detailed results are listed under the location-by-location summaries. Initial results were confirmed by Dr Annette Broom and Dr David Smith at the University of Western Australia, and their assistance is gratefully acknowledged.

Table 2. Sentinel Chicken Flavivirus Seroconversions, 2000-2001.

In response to the MVE activity, several actions were taken:

• Additional sentinel flocks were established in the northeast inland at Moree and Wee Waa in early March, but no seroconversions were detected.

• For the majority of sites that had activity, the sentinel chicken flocks were supplemented with new birds (i.e. birds that were seronegative).

• The bleeding season was extended to the end of May.

• Opportunistic testing of chickens was undertaken in the northeast inland by the relevant Public Heath Unit, in conjunction with ICPMR.
  

Opportunistic Testing

The opportunistic testing comprised the bleeding of chickens from randomly selected properties in the locations depicted in Table 3. The blood samples were then tested for the presence of flavivirus antibodies as per the sentinel chicken flocks. This type of sampling provides a ‘snap-shot’ of activity and can afford a measure of geographical virus spread. The only location that had any seropositive chickens was the opportunistic flock at Macquarie Marshes, which had four KUN seropositive birds.