and crew
mysteries of mosquito-borne illnesses

Dr. Reid Gerhardt
and his students are finding that tracts of forests may factor in
the spread of
LaCrosse Encephalitis
in Tennessee.


by Lisa Byerley Gary

When Dr. Reid Gerhardt and his team of research associates and students go outside, they specifically look for critters most of us take pains to avoid. They watch for mosquitoes, examining which types can be found in which areas. And this summer they’ll be looking for furry pests as well—the squirrels and chipmunks that may harbor mosquito-borne diseases.

Gerhardt, a professor in entomology with 40 years of mosquito research on his dossier, doesn’t get tired of the blood-sucking insects. “It’s what I do,” he says.

What he does has always been important to the rest of us, but with West Nile virus and La Crosse encephalitis making headlines in recent summers, mosquito research is taking on even greater significance.

Asian tiger mosquitoes, a particularly aggressive breed known for biting even in the heat of the day, are implicated as carriers of both diseases and “are in almost everyone’s back yard,” Gerhardt says. But how do mosquitoes get the diseases?

Blood-sucking insects are attracted to most warm-blooded animals and carry diseases from one species to another.

“What we’re doing this summer is collecting blood samples from squirrels and chipmunks from areas in and around Knoxville, Nashville, and Memphis. It’s a long state and the diseases vary from one end to the other. Memphis has high West Nile areas. Knoxville has clusters of La Crosse.”
His team will target two spots in each of the three areas—one known for low disease activity and the other for high disease presence. Live trapping methods, done under the supervision of an animal care
committee, will “harm the animals in the least way possible,” Gerhardt says. Scientists will examine blood samples for the presence of both diseases.

Understanding the transmission of these diseases between humans and animals is complex. Gerhardt works closely with Tennessee’s medical entomologist, Kristy Gottfried, a UT graduate who previously worked for the Centers for Disease Control. Her work makes it easier to collect medical and other data statewide to correlate with UT research.

On Gerhardt’s office wall is a map of Tennessee with pins marking known outbreaks of West Nile and La Crosse. That diseases appear in clusters is abundantly clear. This summer he hopes their work will add yet another overlay to the map—presence of the two diseases in rodent populations. If that data corresponds with the outbreak clusters, the total picture becomes more clear and control methods can be developed that hit the diseases at their source.

And just what is that source of the cluster outbreaks? For La Crosse, the UT team has its suspicions.
“We’re suspicious about large, unbroken forest areas,” Gerhardt says. If (medical professionals) continue to tell us about new cases so that we can map them and if we can line up physical features on the ground with where the cases are, then we may know for sure.”

West Nile gets lots of press, Gerhardt says, but La Crosse encephalitis is probably underreported and underappreciated as a threat because doctors often don’t find the exact cause of a virus when the treatment will be the same regardless. Yet La Crosse threatens at-risk populations, especially children younger than 15, and over the past six years in the greater Knoxville area, 12 to 15 people a year have been hospitalized with it. Though the virus is rarely fatal, the cost to families and to society is enormous, often involving hospital care and follow-up treatment.

Eliminating the disease requires understanding it. If Gerhardt’s team can relate disease-carrying rodents to outbreak areas, the next step may be a comprehensive control plan.

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