What is the VecTest?
The VecTest is an antigen panel assay designed by Medical Analysis Systems, Inc to specifically test for West Nile Virus (WNV), St. Louis Encephalitis (SLE) and Eastern Equine Encephalitis (EEE). The VecTest operates by way of a rapid detection dipstick. Mosquitoes are ground up using a grinding solution and then the dipstick is placed in the slurry. If WNV, SLE, or EEE is present, the antigen will bind to the specific antibodies on the test strip producing a reddish color change on the stick. It should be noted that the assay shows if the antigen is present, it is not meant to be a quantitative assessment of viral antigen in the sample. Though the color intensity of the antigen reaction is a relative indication of the amount of virus in a test sample, the numerical amount can not be determined, or whether virus present is due to one or more infected mosquitoes in the same sample.
How does NWMAD use the VecTest?
During the mosquito season we collect adult mosquito pools to test for WNV/SLE/EEE. A mosquito pool is a collection of mosquitoes (usually about 50) of any given species that is likely to carry/transmit a virus. Since stagnant water Culex mosquitoes are the primary mosquitoes implicated in transmission of WNV and SLE they are collected in special traps called "gravid traps".
The advantage of using gravid traps is that it targets female Culex mosquitoes. The tub of the gravid trap is filled with stagnant, vegetation-enriched water made to replicate the normal larval habitat of the Culex mosquito. The female Culex mosquito will take a blood meal and then actively search out a suitable habitat on which to lay her eggs. This female will subsequently get caught in the trap. If the blood meal that she had taken was from a host infected with WNV, SLE, or EEE, then it will produce a positive VecTest sample.
By keeping track of positive VecTest mosquito pools we can monitor the distribution and the frequency of these viruses in the District. A positive mosquito pool means that local mosquitoes are infected with the virus and possibly capable of transmitting it to other hosts including humans. The sensitivity level of the VecTest by design indicates infected mosquitoes likely to infect humans. Multiple VecTest infected mosquito samples from the same locality also indicate an increasing risk of acquiring West Nile Virus (especially in July-September in Illinois). By combining the VecTest results and total numbers of mosquitoes collected along with bird surveillance records and horse and human viral infection data, we can adapt and enhance our control practices and further reduce the potential for human transmission.