Mosquitoes Expected to Bite, Not Transmit Virus This Summer

Photo of Dr. Christina Frazier testing mosquitoes in the Southeast Missouri Arbovirus Lab

Dr. Christina Frazier tests mosquitoes in the Southeast Missouri Arbovirus Lab to determine if they are vector mosquitoes — the type that transmit virus.

CAPE GIRARDEAU, Mo., July 7, 2011 — Missouri residents in areas impacted by flooding this spring and summer can expect pest mosquitoes that will chase and bite but likely will not transmit virus, according to a mosquito borne virus expert at Southeast Missouri State University.

Dr. Christina Frazier, professor of biology and director of the Southeast Missouri Arbovirus Lab, says this area can expect a bumper crop of Aedes vexans this summer, a type of pest mosquito which has already shown up in significant numbers in Mississippi County. Aedes vexans eggs are laid on drying ground and hatch during reflooding.

Aedes vexans lay their eggs on the edge of water, and they dry out,” Frazier said. “But when water then covers them, they hatch out. There will be hoards after a flood. There will be a big boom of these this summer. If we are getting lots of mosquitoes, these are the type we will get.

“Right after a flood, we can expect to see an increase in pest mosquitoes,” she said.

At this point in the summer, Frazier said the St. Louis County Health Department  normally would be collecting 200 mosquitoes a night in a trap. Recently, they have collected more than 1,000 per night.

Frazier says Missouri residents should be especially cautious about puddles left behind by recent flooding as they attract vector mosquitoes – the type that transmit virus.

“Everybody should be responsible for their own yards to make sure they don’t have spots holding water,” she said, adding that old paint cans, old swimming pools that are semi-dried up and old tires are likely culprits. “If you have a lot of these items around, you are generally a breeding ground right in your own yard. We are better off if everyone cleans up their yards so we have fewer mosquitoes.”

Frazier and Karen Yates, vector borne disease coordinator with the Missouri Department of Health and Senior Services, Office of Veterinary Public Health, train local health departments in Missouri to trap mosquitoes. County health departments in Butler, Jasper, Cole, Nodaway, Boone, Henry, St. Louis, Clay and Taney counties participate in the program.  The departments trap and send mosquitoes each week from

May to September to Southeast’s Arbovirus Lab. The lab determines if they are vector mosquitoes – those carrying either West Nile Virus or St. Louis Encephalitis.

St. Louis County recently sent 30,000 Culex pipiens complex mosquitoes – a type which can transmit virus  — to the lab. Six were determined to be carrying the West Nile Virus, Frazier said, however no mosquitoes carrying St. Louis Encephalitis have been identified yet this summer.

Fortunately, she says, no vectors have been found among the mosquitoes collected recently from the Birds Point levee area in Mississippi County.

“Culex mosquitoes need organic rich spots to survive,” Frazier said. “Lots of little puddles have created lots of breeding sites,” though.

Frazier says hot, dry summer days will initially shrink these to be better more nutrient rich breeding places, but if the conditions continue long enough they will eliminate these spots.  Wet weather, she added, will continue to keep these numbers elevated.

Southeast’s Arbovirus Lab maintains a password protected website, courtesy of Southeast Missouri State University’s Center for Scholarship in Teaching and Learning, that allows it to communicate information with local health departments and the state health department in Missouri. The state in turn provides data to the Centers for Disease Control. County health departments also use the data to inform the public about the number of mosquitoes collected and tested from their county and the number of positive tests for vector mosquitoes, Frazier said.

She said counties use the information to guide their spraying practices and also to educate the public with tips on avoiding mosquitoes, such as:

• Wear mosquito repellent when outdoors• Avoid going out from dusk to dawn• Wear long sleeved shirts if you are outdoors

Frazier holds a doctoral degree in virology/epidemiology/immunology and arbovirus epidemiology with an emphasis on West Nile from Yale University. She has been researching mosquitoes in Missouri for 30 years. She also serves as associate to the provost for data analysis and assessment at Southeast.