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NSW Arbovirus Surveillance & Vector Monitoring Program |  |
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NSW Arbovirus Surveillance & Vector Monitoring Program | |
 1998 - 1999
Annual Report  |
SENTINEL
CHICKEN FLOCK PROGRAM
The
NSW Department of Health has funded chicken sentinel programs for surveillance of the
flaviviruses MVE and KUN since 1979. MVE and KUN are thought to exist in a
natural cycle between mosquitoes and birds (particularly water birds such as the Nankeen
Night Heron). As both viruses are primarily bird viruses, chickens were chosen as a
suitable host. Young birds are more susceptible to infection with these viruses and this
is the reason that 6 to 12 week old chickens are deployed each year. The birds are bled
weekly and tested for the presence of flavivirus antibody. If birds become positive (i.e.
seroconvert) to a flavivirus, additional tests are performed to determine whether the
infection is due to MVE or KUN.
Seroconversion
in the sentinel flocks provides evidence that the level of virus in mosquito populations
has increased sufficiently for transmission to occur. As the sentinel flocks are located
in potential "hot spots" and are exposed to potentially infected vectors 24 hrs
a day from late spring, it is reasonable to assume that transmission in chickens will
precede the appearance of human infections. However, this assumes that there are
sufficient flocks and that are deployed in the most appropriate locations. This premise
has held true during the summer of 1990-91 in NSW and has frequently provided early
warning of increased viral activity in the Northern Territory and north-west Western
Australia.
This
season the chicken sentinel component of the program started later then usual because of
the need to gain ethical approval for the use of animals. The Animal Ethics committee at
Westmead Hospital gave approval for the use of chickens in the program and flocks were
deployed in January rather than November.
Flocks
are usually deployed to ensure coverage of the major river systems (Murray, Lachlan,
Darling and Murrumbidgee rivers). This season, six locations (Bourke, Deniliquin, Forbes, Macquarie Marshes, Menindee and two flocks at Griffith) received flocks in
January. Another flock was deployed at Leeton in March following a KUN isolate from
mosquitoes and the season was extended to the end of April.
There
were no seroconversions detected this season in the flocks. Although there were reports of
three human KUN infections
from the Riverina, two occurred in late 1999 prior to the deployment of the flocks and the
third in early 1999 in an area with no flocks.
With
the annual review of methodologies, changes were made this season to the type of blood
collection tubes used by the collectors. The complete methods are on the web at:
<http://www.arbovirus.health.nsw.gov.au/arbovirus/about/chickenmethods.htm>
This
change has resulted in better quality samples, which has reduced the need for retesting by
60%. This combined with the incorporation of the program onto Westmead Hospital's
pathology computer system (Cerner-Pathnet) has reduced the turnaround time. Most results
are available on the day of receipt or the following day. Reports are faxed to the public
health units and included on the web site.
Plans are underway to computer generate and auto-fax reports in the next season. In addition, it is envisaged that a workshop be held at Westmead for the flock handlers that would further enhance the program.
