As reports of the West Nile virus arrive from across the United States this week, experts said the virus’s impact in Michigan still remains to be seen. News reports said mosquitoes carrying the virus have been found in Nevada, California and Washington. But as of Tuesday, there have been no reported cases of West Nile in humans or mosquitoes in Michigan this year. Since the virus’s outbreak in Michigan, MSU became the state’s central testing point for birds and mosquitoes, said Michael Kaufman, an MSU professor of entomology. Human cases of West Nile typically peak during late summer, following a rapid increase in infected mosquito populations, he said.
Human cases of West Nile in North America, which are contracted through infected mosquitoes, first appeared in 1999 in the New York City area. By the time the virus’s presence in Michigan birds and mosquitoes was detected in 2001, it had gained national attention, and federal funding went to monitoring it.
West Nile spiked among Michigan residents in 2002 with 644 cases and 51 deaths, said Dr. Mary Grace Stobierski, public health veterinarian for the Department of Community Health. In 2007, there were 16 human cases of West Nile and four deaths, equaling 2004 for the lowest number of reported human cases since the original outbreak.
About 20 percent of people infected with West Nile show symptoms, which include fever, fatigue and swollen lymph nodes. About one in 150 will develop more severe symptoms like dizziness, seizures and death. Because the types of mosquitoes that carry West Nile thrive in hot, dry conditions, the virus’s prevalence this year remains unclear, Kaufman said.
“It’s still really early,” Kaufman said. “I don’t think it’s going to change unless conditions change. It may be that it’s ramping up slowly.”
Testing at MSU
West Nile, traced back to birds from central Africa, will probably never completely disappear from the country.
And although its frequency in Michigan residents dropped following its 2002 peak, it’s still important to monitor, said Ned Walker, a professor in MSU’s Department of Microbiology and Molecular Genetics.
Beginning in May and continuing through October, Walker and his team of graduate and undergraduate MSU students collect thousands of mosquitoes in southern metropolitan Chicago and monitor them for the virus. The study is in its fourth summer of research.
This year the National Science Foundation renewed the study, conducted in collaboration with the University of Illinois, for $1.3 million over five years, of which MSU will use about $500,000.
At MSU, microbiology and genomics students determine which mosquitoes are infected and what animals they fed on. Culex mosquitoes are infected when they feed off of infected birds, and they in turn transfer the virus to other birds, humans, horses and various animals, Walker said.
Part of the study is investigating which species of birds typically carry the virus. The data gathered since 2005 found the American robin, Michigan’s state bird, to be one of the virus’s more prevalent carriers.
“Usually beginning early to middle July, the virus infection in the mosquito population increases rapidly,” Walker said. “It increases so rapidly that something seems to be triggering it.”
The study tied the increase of infected mosquitoes to times when there are many birds hatching.
“(The young birds) can’t fly yet and they’re vulnerable to mosquito bites because they sit around in the trees,” Walker said.
When other mosquitoes bite the infected young birds, the number of infected mosquitoes increases rapidly.
“We see (the percentage of infected mosquitoes) go from about zero to about 6 percent in three weeks,” Walker said. “It’s then that the human cases start to appear.”
Amy Wechsler, a microbiology graduate student working on the study, said she likens the study to a forensics investigation.
“We can find out more about how the disease is transmitted from the mosquitoes,” she said. “We can learn about the biology and ecology of the virus.”
Decline in federal funding
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Since 2003, the Centers for Disease Control and Prevention granted federal dollars on an annual basis for state and local health officials in Michigan to monitor the virus’s progress, Stobierski said. This year, the organization planned to disburse approximately $26.3 million nationwide to monitor West Nile.
At that time, MSU adopted a method to test tissues for West Nile, Kaufman said.
In 2008, the state received about half of what it received during the virus’s peak years, Stobierski said. As funding declined, so did testing dead birds, horses and mosquitoes.
“We can’t gauge it as closely because the amount of testing for all these species has decreased,” she said. “If you lose your testing for them, you decrease your ability to predict the presence of a disease in a given geographic area.”
Although MSU doesn’t receive as many samples now as it did in 2002, students still get some mosquitoes to test from mosquito control and community health groups, Kaufman said.
“The more we understand about how it works, the better we’ll understand about some of the diseases that are similar to it,” he said.
For students, testing for West Nile can be a way of contributing to the community.
“It’s nice to feel like you’re helping the common good,” said Michael Charlot, a genomics and molecular genetics senior working with Walker’s study. “West Nile surveillance — it’s part of maintaining the public health.”
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