DelVal mosquito experts weigh in on the West Nile Virus hitting Bucks County
Aug 30, 2012
A Culex, the type of mosquito responsible for spreading West Nile Virus, lays eggs.
Cases of West Nile, a virus spread by mosquitoes, are up this year, and a case has been reported in
Bucks County. Two DelVal biology faculty members who have done research related to mosquitoes offer some insight on steps to reduce the risk of contracting the virus, as well as the insect that carries it.
According to the Center for Disease Control and Prevention only about one in every 150 people with the virus becomes seriously ill. The most serious cases cause symptoms such as: high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis, and neurological effects that may be permanent.
Milder symptoms, which occur in up to 20 percent of infected people can include: fever, headache, body aches, nausea, vomiting, and sometimes swollen lymph glands or a skin rash on the chest, stomach, and back.
Weather and the virus
According to Chris Tipping, Ph.D, a biology faculty member who earned his doctorate in entomology and nematology from the University of Florida, the spread of the virus really depends on the weather.
“What is ideal for this type of mosquito, is if you have one to two pretty good rain events a week during the summer,” said Tipping. “Most breed in foul water, water with high organic material. It has been a pretty good time for mosquitoes. We’re starting to see an increase in the numbers because of that. The more mosquitoes you have, the greater the chance of the virus spreading to humans.”
He said the fall weather will be important.
“If we have a very dry fall, we’re going to see numbers of mosquitoes decline and subsequently cases of the virus also decline,” said Tipping. “If we continue to have rain every few days and it stays warm, the populations could increase and instances of the virus could also increase. It really depends on the weather, what we need is dryness and quick cold.”
The need for blood
The Culex mosquito is the type responsible for spreading the virus. Tipping has expertise in that type of mosquito’s biology, especially how and where they lay their eggs.
He has published some of his research in The Journal of Insect Behavior on mosquitoes and has studied them for about 10 years.
“The interesting thing about these mosquitoes, is that they feed primarily feed on birds,” said Tipping. “They acquire the virus from infected birds as they feed, when birds leave the area to migrate during late summer and fall months, the mosquitoes then seek blood meals from mammals including humans.”
He said females need blood to develop batches of eggs.
Females that have mated seek a blood meal (a bite). After they grab the blood, they change that blood into eggs.
“They lay their eggs in an interesting fashion, in a floating egg raft,” said Tipping. “Those will hatch in a day or two. The warmer the water the quicker they hatch. They develop in as quick as 10 days.”
Tipping said females lay multiple batches of eggs. So, if one bites an infected bird and lays her eggs, a day or two later she will seek another blood meal and potentially spread or vector the virus.
“If they’re lucky they can produce three or four batches,” said Tipping.
Treating high population areas
Ronald Johnson, DelVal’s biology department chair, and some DelVal students were hired by the Bucks County Department of Health about eight years ago to track mosquito populations, to help identify areas that should be spot treated. They worked on the project for two summers.
“We were part of teams that went around to areas where mosquito concentrations were high,” said Johnson. “We would sample, preserve specimens, and enter the info into a database that went to Harrisburg. If the concentrations were above certain densities, they would spot treat areas.”
The group was given maps where the Township said neighbors were complaining about mosquitoes.
“Some of our traps were kept near a big tire dump, and one was at a sewage treatment facility in Quakertown,” said Johnson. “We used small amounts of carbon dioxide to capture them live. A fan would push them up, and we would do the counts.”
He said the goal was to avoid area-wide spraying.
He said spot treating may have been a preferred method in the past because spraying can bring controversy.
“As soon as you mention spraying, you have protest groups,” said Johnson. “It becomes rather debated and controversial.”
Tipping said some counties use aerial spraying, from helicopters and planes, while others use fog trucks.
“Fogging-trucks produce a mist that contains a pyrethroid chemical that has a low mammalian toxicity, but you don’t want to be standing behind the truck,” said Tipping. “Fog trucks are effective, the fog is pretty thick and if it isn’t too windy, it lays around in the low areas where Culex and other pests tend to hide. As it gets dark they fly and they get caught in the fog and die.”
Tips to reduce risk
Johnson and Tipping offered the following tips to reduce the risk of contracting the virus:
• Wear clothing that covers exposed skin.
• Keep bird baths clean and fresh.
• Make sure gutters are clean and free flowing.
• Dispose of any old tires.
“You couldn’t design a better incubator for mosquitoes than a tire,” said Johnson. “It’s warm, traps water, and wind won’t affect the water in the tire.”
• Use bleach to kill mosquitoes living in a tire if it can’t be disposed of.
• Look for containers that might have grass or leaves and now have water. Tipping said those are perfect breeding sites.
• Limit activities at dusk because the mosquitoes become active when the sun sets.
• Use repellant with DEET.