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NSW Arbovirus Surveillance & Vector Monitoring Program |  |
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NSW Arbovirus Surveillance & Vector Monitoring Program | |
 2000 - 2001
Annual Report  |
The aim of the Program is to provide an early
warning of the presence of Murray
Valley Encephalitis (MVE) and Kunjin (KUN) viruses in the
state in an effort to reduce the potential for human disease. In addition, it compiles and
analyses mosquito and alphavirus (especially Ross River and Barmah Forest virus) data
collected over a number of successive years. This will provide a solid base to determine
the underlying causes of the seasonal fluctuations in arbovirus activity and the relative
abundance of the mosquito vector species affecting the well-being of human communities.
This information can then be used as a basis for modifying existing local and regional
vector control programs, and in the creation of new ones.
Arbovirus Surveillance can be divided into two categories: those methods that attempt to predict activity and those that demonstrate viral transmission. Predictive methods include the monitoring of weather patterns, the long-term recording of mosquito abundance, and the isolation of virus from vectors. Monitoring of rainfall patterns, be it short term with rainfall or longer term with the Southern Oscillation, is critical as rainfall is one of the major environmental factors that influences mosquito abundance; generally the more rain, the higher the mosquito numbers. The long-term recording of mosquito abundance can establish baseline mosquito levels for a location (i.e. determine what are normal populations), and this allows the rapid recognition of unusual mosquito activity. The isolation of virus from mosquito vectors can provide the first indication of which arboviruses are circulating in an area. This may lead to the early recognition of outbreaks and be a sign of the potential disease risks to the community. Virus isolation can also identify new virus incursions, lead to the recognition of new virus genotypes and identify new vectors.
Methods that demonstrate arboviral transmission
include the monitoring of suitable sentinel animals (such as chickens) for the presence of
antibodies to particular viruses (e.g. flaviviruses) and the recording of human cases of
disease. Sentinel animals can be placed into potential ‘hotspots’ of virus
activity, and as they are not protected from mosquito bites, may indicate activity in a
region before human cases. In general terms, for arbovirus surveillance, the monitoring of
human cases has little direct value, as by the time the virus activity is detected in the
human population, not much can be done to control the virus. Via the other methodologies,
the aim of the surveillance program is to recognise both potential and actual virus
activity before it impacts greatly on the human population. The recording of human
infections does however provide important epidemiological data and can define the
locations where surveillance should occur.
These methods of surveillance are listed in order;
generally with the more rainfall, the greater the mosquito production. The higher the
mosquito production, the greater the probability of enzootic virus activity in the
mosquito population. The higher the proportion of virus infected mosquitoes, the greater
the probability of transmission and thus the higher the risk to the human population. The
NSW Arbovirus Surveillance and Mosquito Monitoring Program undertakes the first four
methods of arbovirus surveillance and the results for the 2000-2001 season follow.
For 2000-2001, mosquito trapping sites were operated at 17 inland, 5 coastal and 6 Sydney locations (Fig 1). Chicken sentinel flocks were initially placed at 10 sites. Moree and Wee Waa flocks were established late in the season.
 Fig 1. Mosquito trapping locations and Sentinel Chicken sites, 2000-2001. |
