DiagnosticsDo Chicago's Suburbs Hold The Key To Understanding West Nile Virus?
When Tony Goldberg is not whacking through the brush of central
Africa, one of the world"s great cauldrons of emerging human and animal
disease, he is scouring another disease hot spot: the southwestern suburbs
of Chicago.
For Goldberg, an epidemiologist and a professor at the University of
Wisconsin-Madison"s School of Veterinary Medicine, the Chicago suburbs
near Oak Lawn are the perfect laboratory for prying loose the secrets of
West Nile virus, a pathogen carried by mosquitoes and birds that infects
and sickens thousands of people each summer.
"A characteristic of West Nile virus is that it often affects people in
urban and suburban settings," says Goldberg of a virus that, as its name
implies, has its origins in the Old World of Africa and the Middle East.
"But the pattern of disease across the urban landscape isn"t uniform. It
is more common in some places than others."
And Chicago - especially its suburbs like Oak Lawn, Goldberg says - seems
to harbor the perfect combination of factors to give the virus an
epidemiological leg up. "Chicago is one of the cities most affected by
West Nile virus," says Goldberg, whose research group is scouring the
lawns and thickets of Oak Lawn and surrounding areas in search of the
reservoirs of disease.
In the case of West Nile, the key players are mosquitoes and birds, which
carry the virus that can cause potentially fatal encephalitis or
meningitis in humans, according to Gabe Hamer, a UW-Madison postdoctoral
fellow who is leading the field effort in Oak Lawn. The disease is spread
to people through the bite of the mosquito, which becomes infected by
feeding on birds that carry the virus.
"It was found early in the discovery of West Nile virus in North America
that certain bird species seemed to be important," Goldberg explains,
noting that larger birds such as crows and blue jays seemed to be
especially prone to infection. "It turns out that they are very
susceptible to the virus, but they are not the most important species for
amplifying the disease. In Chicago, there is one bird species that stands
out above all others as a driver of West Nile amplification: the robin. It
is the indisputable super spreader of the virus in the Chicago region."
In particular, says Goldberg, whose group is identifying blood meals of
mosquitoes and using radio telemetry by mounting transmitters to robins to
study their movements, it is young, recently fledged robins that seem to
be the ideal hosts for the pathogen. "While they carry the virus, they
seem to be more resistant to the disease than other birds, there are lots
of them and they seem to be good at transmitting West Nile at just the
right time of year," he says, noting that crows and jays typically die not
long after infection.
Because robins can sustain the virus, they become a key reservoir of the
pathogen, infecting the mosquitoes that feed on them and amplifying the
cycle of infection, says Hamer.
The curious epidemiological puzzle of West Nile is that while some places
in suburban Chicago seem to be hot spots for the disease, similar
environments across the North American landscape have a much lower
incidence of the disease.
"We see variation among cities and within cities," says Goldberg,
explaining that cities such as Atlanta and Madison have many of the same
environmental attributes and species affected by West Nile, but see much
lower incidence of disease in people. "We see flare-ups in certain
environments, but not in similar environments, or even in similar
environments near a hot spot."
The goal of Goldberg"s study is to ferret out the reasons why one
neighborhood might be in the eye of the West Nile storm while another
neighboring area is not. "We are comparing adjacent neighborhoods a few
kilometers apart, which is a finer scale in urban environments than anyone
has studied before," he says.
His group, which includes teams of students, postdoctoral researchers and
collaborators from the University of Illinois, Michigan State University
and Emory University, is tracking the movements of robins using radio
transmitters and searching for their hidden nighttime roosts. They are
also recording climate and weather data, as well as local patterns of
vegetation, in an effort to tease out the factors that contribute to
disease.
Next year, Goldberg, with the help of a group led by Ned Walker of
Michigan State University, hopes to track the movement of mosquitoes
across the suburban landscape using chemical isotopes found in the
insects, which can pinpoint where they hatched.
The idea, says the Wisconsin researcher, is to identify the factors that
cause a flare-up of disease at a particular place in time.
"If you can find those places and the reasons why disease occurs in one
place and not another, that points to obvious avenues for intervention and
disease prevention," argues Goldberg.
The study is funded by the National Science Foundation and the National
Institutes of Health through their joint program in Ecology of Infectious
Disease.
University of Wisconsin-Madison