Monitoring Data

The Lancaster County WNV – Mosquito Control Program began monitoring the virus in 2001.  Our county is 969 square miles, and to date, approximately 600 sampling sites exist. A PDF presentation of the data can be downloaded here. On the first slide, a table displays sampling data by year including the total number of mosquitoes and samples collected, the average number of mosquitoes collected per sample, average rainfall and temperature during the mosquito season (April 1 – October 31), and the number of positive mosquito pools detected.

The average number of mosquitoes collected per sample indicates the abundance of the mosquito population for each year, and the second slide is a bar graph that shows the relationship of mosquito abundance to the amount of water available for breeding.  This confirms the common sense notion that more standing water produces more mosquitoes.

Fortunately, in 2009 there were no confirmed human or horse West Nile cases in the county; however, 33 positive mosquito pools were collected, making us the third most active county in the state.  A table on the third slide lists the general location and collection date of the mosquitoes which carried the virus.

Slide number four is a line graph that records the nine year trend of virus activity as shown by the mosquito population.  The virus was most active in 2003 when 83 positive mosquito pools were detected, and from 2005 to 2008, activity flat-lined at 12.5 positive pools per year.  Virus behavior is generally cyclic in nature: there is an initial surge, followed by a leveling-off as organisms build up immunity.  And then, approximately every seven years, activity flares up again.  Last year’s positive spike could be an indication of a resurgence of the virus.