West Nile Virus Found in North Fork Mosquitoes

For the first time this year, West Nile Virus (WNV) has been detected in mosquitoes from the North Fork Valley.  A composite sample collected by the North Fork Mosquito Abatement District on Aug. 19 was submitted for testing, and the District received the positive test result on Sep. 1.

North Fork MAD is planning to fog the suspected area as soon as possible.

The Colorado State Health Department laboratory in Denver, which normally tests mosquito samples for WNV, was closed earlier this summer because of lack of funds.  However, Ken Nordstrom from the Delta County Health Department found several test kits left over from last year that enabled the testing to be done by a laboratory in Grand Junction. 

Tests require approximately 50 Culex mosquitoes in a sample.  Total numbers of mosquitoes trapped throughout the valley have been very low recently due to North Fork MAD's aggressive larviciding program.  In order to provide sufficient mosquitoes for the test, specimens from six different trapping sites on Lamborn Mesa, Bone Mesa and Stewart Mesa were submitted together. 
 
Short of funds and with no paid staff, North Fork MAD responded immediately to the Health Department report by zeroing in on the six suspected sites.  The most recent trapping data had shown that four of the sites had negligible mosquito counts and could thus be eliminated.  Numbers at the two remaining sites, although still low, were high enough to justify retesting.  Volunteers were sent out to set traps at these two sites, one on Lamborn Mesa, the other on Stewart Mesa.
 
The next morning, volunteers collected the traps, and took them back to the District's "Bug House" where the trapped mosquitoes were frozen, counted and identified as to species.  Species identification is necessary because only certain types of mosquitoes carry and transmit West Nile Virus. 

Only four mosquitoes (one of which was Culex) were collected at the Lamborn Mesa site.  Fifty-one were trapped at the site on Stewart Mesa, 35 of which were Culex.

The North Fork MAD Board quickly decided to spot-treat the Stewart Mesa site with the adulticide Aqualuer, a synthetic pryethoid with permethrin in an orange-oil base.

The spraying will take place this week, as soon as residents can be notified.  Organic farmer and North Fork MAD President Kris Kropp will operate the spray truck himself in order to spare the District the expense of hiring a pesticide applicator.

Like state and county agencies across the country, North Fork MAD has been hit with budget shortfalls this year as a result of diminishing property tax collections.  Revenues collected for the District by the County are down 19% compared to last year.  As a consequence, the District's field manager and staff had to be laid off last month.   Mosquito abatement efforts are currently being carried out by board members and volunteers. 

Board member Robin Smith said, "If we had the advantage of state testing, we could pinpoint the site where we have WNV-infected mosquitoes.  But lacking that, our best option is to target the suspected area with the highest numbers." 

"The Stewart Mesa site is a good example of a mosquito breeding site that needs mitigation," Smith added.  "And we will be working with property owners to try to find a permanent solution."  

The Stewart Mesa site is adjacent to an extensive series of cattail-infested bogs which collect irrigation run-off.  North Fork MAD field crews have treated these areas with larvicide several times over the course of the summer, but the thick vegetation makes it difficult for the larvicide material to disperse evenly and completely eliminate mosquito larvae.

Board member Rosemary Bilchak said, "A positive report of WNV from the state is a red flag event for us.  We know that fogging from trucks is one of the least effective ways to eliminate mosquitoes.  But we want to do everything in our power to prevent the first case of West Nile Virus from happening here in the valley this year."

Week Ending July 31, 2009

Week Ending July 3, 2009