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Mosquito and Disease Surveillance History

Mosquito Surveillance

With the formation of the Mosquito Abatement District- Davis in 1953, Dr. Don Rees was commissioned to do a mosquito surveillance survey in Davis County to supply a baseline of the current mosquito population. By 1976 an established surveillance program was supplying consistent data on the mosquito population. The program used New Jersey Light traps (NJLT) in twelve to sixteen designated locations throughout the county. NJLT allowed for continual monitoring of the mosquito population during the summer. The challenge with NJLT is they need a dedicated power source limiting the locations where traps can be placed. The use of these traps continued each summer until 2015.

In 2016 carbon dioxide (CO2) baited CDC light traps replaced the NJLT as the preferred surveillance trap. In making the switch over it allowed for greater flexibility in surveillance locations, allowing traps in areas of greatest concern. CO2 baited CDC light traps attract a wider range of mosquito species and trap less non target insects. They are the preferred trapping method for many districts in the United States.

The introduction of West Nile virus (WNV) into New York in 1999 altered the focus of the surveillance program, WNV made its way to Utah in 2003. Starting in 2002 five CDC light traps baited with dry ice were added to the surveillance program. Over the following years that number increased to twenty-four. In 2023 the number of traps increased to thirty-two weekly set traps.

Disease Surveillance

Disease surveillance started in 1983 with a focus on Western equine encephalitis (WEE) and St. Louis encephalitis (SLE). The surveillance was managed with sentinel chicken flocks, which were kept by the district. Between 1983 and 1993 the district had two flocks, in 1993 the number of flocks increased to twelve with a total of sixty chickens being maintained. These flocks were actively used in disease surveillance until 2014 when the cost of testing and maintaining the flocks became a challenge.

As West Nile virus (WNV) spread across the United States, it was added to the list of tested viruses in the district. WNV was first detected in Davis County in 2004 and has been routinely found in mosquito pools since then.

For many years, all virus testing was done by State or University labs. In 2014 the district started the process to bring disease testing in house, with the goal of decreasing the trapping to response time delay. From 2014 to 2018 the testing method RAMP was used to test the desired mosquito species for WNV, SLE, WEE. In 2018 the district moved to the more sensitive and accurate RT-PCR testing procedures.

The district monitors WEE, SLE and WNV starting in June and going to the end of September. WNV will often start appearing in mosquito pools in July. We report our weekly findings to the Utah Department of Health and Human Services.