Jun 302009
Authors: Madeline Novey

The first mosquito testing positive for the West Nile virus was trapped in Larimer County June 5, making it the earliest in annual spring comparisons by about three weeks, officials said last week.

Both city and mosquito control officials agreed the mosquito was most likely an overwintering female – an infected mosquito that survived the winter as a larva and developed into an adult in the spring – but said it is too early to determine how this year’s West Nile season will be.

“It’s quite obviously too early to say how the season will be,” said Jessica Schurich, the operations

manager for the City of Fort Collins and Loveland, saying experts are not sure if the early trapping is an indicator for high numbers of mosquitoes.

West Nile virus, historically occurring in Asia, Africa, the Middle East and Eastern Europe, is contracted by adult mosquitoes and transferred to humans when a female bites an animal or human.

West Nile is a seasonal epidemic running from summer to fall in North America, according to the Center for Disease Control, and only an estimated one in 150 people infected with the virus will contract a severe illness –/high fever, tremors, coma, muscle weakness and paralysis.

However, four out of five people, or 80 percent, who contract it show no symptoms.

Though Mosquito Control has not trapped additional infected mosquitoes since June 5, Schurich said they are seeing elevated numbers of “Culex pipiens” larva, one of two species of mosquito that carries the West Nile virus, in waters across the city. “Culex tarsalis” also transmits the virus.

Since mosquitoes are drawn to bodies of standing water – marshes, puddles, irrigation pastures and plant pots, among others – recent rains and increased spring moisture are possible factors of the larval increase. The next few weeks of testing by Mosquito Control will better determine the numbers of infected mosquitoes, Schurich said.

When Mosquito Control finds the larvae in standing water, it treats the water with an environmentally friendly insecticide to kill them, said Mike Calhoon, crew chief with the Parks Division of the City of Fort Collins.

This is part of the “West Nile mitigation business,” Calhoon said of the effort to prevent the mosquitoes from reaching adulthood when they (only the females) are able to bite and transfer the virus to humans and animals.

“Our hope is to beat them out of the water,” he said.

In addition to testing local waters and killing larva, Mosquito Control set 43 adult mosquito traps weekly across Fort Collins, placing the last 10 in the southwest corner of the city Friday night. It was in these traps the mosquito testing positive for West Nile was captured and tested by CSU researchers.

For the last five years, the CDC tested the trapped mosquitoes as part of a national study on the rates of infection of mosquito-borne illnesses. The city this year is paying a group of CSU researchers to complete the testing.

If the number of infected adult mosquitoes in the city were to rise, Calhoon said an advisory panel would review the need to spray insecticides into the air. After a series of recommendations, the city manager would make the final choice.

“We don’t have any plans of what people call ‘fogging,'” he said. “We would only do that after the county Health Department makes that decision to spray aduclticide,” the insecticide designed to kill adult mosquitoes.

Experts agree the best form of combat is prevention and education.

A Mosquito Control employee is sent out to city events, most recently to evening softball games in the city and to the Irish Festival. They advise people on how to avoid bites, including wearing a long sleeve shirt and pants and using bug sprays outside. Calhoon said Mosquito Control, too, will go to people’s home to test and treat standing water.

After the recent rains, Schurich said residents should dump out sources of standing water to prevent further mosquito populations from developing.

Approaching July and August, when doctors traditionally see cases of West Nile, the most “important thing students or anyone can do is avoid mosquito bites,” said Lisa Duggan, the infection control nurse for the CSU Health Network.

Staying in places that are well screened and using insect repellent, especially in the evenings, is imperative, she added.

People who think they might have West Nile should go to Hartshorn Health Services on campus to get tested. And while West Nile shares symptoms with other diseases –/fever, rash and headaches –/Duggan said she encourages students to get tested for the virus.

News Managing Editor Madeline Novey can be reached at news@collegian.com.

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