Dear Editor:
In Chicago, 225 cases of illness from West Nile
virus (WNV) were reported last summer (The
Great Spray Debate, Spring 2003). Many of those
affected have not fully recovered, and 19 died.
In some neighborhoods nearly one in 1,000 residents
became ill.
People would be outraged if
an artificial environmental hazard caused this much
illness and death. In a way, it did. WNV was transmitted
here by Culex pipiens, the northern house
mosquito. These mosquitoes are urban opportunists.
They breed principally in catch basins and other
artificial containers in populated areas.
Elimination of containers that
hold standing water is critical to limiting mosquitoes
that spread WNV. Property owners, concerned citizens,
and city agencies need to work together to make
this a basic part of sanitation.
Catch basins, a necessary part
of our urban environment, serve as ideal breeding
sites for Culex mosquitoes. We currently
use methoprene, an insect growth regulator, for
these. Methoprene is available in a slow-release
formulation that requires only one application per
season to each of the 200,000-plus catch basins
in the city. The bacterial products last 30 days,
and would require several costly re-applications
during the season. Methoprene only affects insects
that develop in treated water, doesn't contaminate
groundwater, degrades quickly into inactive chemicals,
and doesn't bioaccumulate. These characteristics
compare favorably with those of the bacterial larvicides.
Controlling mosquitoes in the
larval stage is always preferable to spraying. However,
spraying is the only way to reduce the number of
infected adult mosquitoes when they threaten human
health. Sumithrin (Anvil), used in Chicago, also
has a favorable profile for a pesticide. It breaks
down quickly in sunlight or water and does not bioaccumulate.
The risk to aquatic species is low: the EPA label
does not require spraying to be set back from bodies
of water. With regard to other nontargeted species,
an ultra low volume application would be expected
to affect mosquito-sized insects that are flying
at night when an area is sprayed. Bees, butterflies,
and dragonflies are larger than mosquitoes and are
typically not flying at night in Chicago, so effects
on these species would be unexpected.
West Nile virus is a significant
public health concern that can be lessened with
citizen action and environmentally responsible mosquito
control methods. At times, this includes judicious
and careful use of pesticides.
William S. Paul, MD, MPH
Deputy Commissioner
Chicago
Department of Public Health
