Global warming and mosquito-borne encephalitis
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Sat Sep 4 08:32:34 MDT 1999
NY Times, Saturday, September 4, 1999
Encephalitis Strikes 3 People, 1 Fatally, in Queens
By ABBY GOODNOUGH
An elderly resident of Queens died this week from a mosquito-borne viral
disease known as St. Louis encephalitis, and city health officials fear
least nine other people have been infected, Mayor Giuliani said. . .
The Washington Post
June 21, 1998, Sunday, Final Edition
HEADLINE: The PEST IN 'PESTILENCE'; When it comes to mosquitoes, think
globally. And exterminate locally
Martha m. Hamilton
Two women follow the grade downhill: past the neat two-story suburban
houses of a development in Largo named Newbridge, past cold, unused
backyard barbecues, past well-tended lawns and gardens, into a wooded
hollow full of sweet gum trees, violets, pink beauties and the polished
bronze of newly emergent poison ivy. There they wade right into a flood
left by spring rains, the water rising to the ankles of their knee-high
boots. Wielding three-foot-long pine handles tipped with white plastic
cups, they dip cupfuls of water and stare at the contents.
Against the stark white, they see a harbinger of summer: tiny T-shaped
squiggles no longer than a quarter-inch and little spheres the size of a
"We've got larvae," says Jeannine M. Dorothy, an entomologist with the
Maryland Department of Agriculture. Specifically, she means the larvae and
pupae of Aedes canadensis. This is a mosquito that transmits heartworm to
dogs, and may spread Eastern equine encephalitis. It also bites humans, to
Dorothy and her partner in mosquito control, Patricia Ferrao, take opposite
sides of the hollow. Every 10 paces, they stop to cast charcoal briquettes
onto the water. The briquettes are impregnated with methoprene, an insect
growth regulator. It is intended to give these mosquitoes-to-be a fatal
case of arrested development.
In about 45 minutes, Dorothy and Ferrao treat nearly an acre of lowlands.
near the end of the pool, Ferrao lobs a briquette to her left.
"Die, larvae," she says.
This is how it begins, each April, with a search-and-destroy mission
mounted in the woodlands surrounding Washington. Aedes canadensis is only
the earliest-hatching of the 58 kinds of mosquitoes that inhabit Maryland,
14 of which present threats ranging from itchy bites to potentially deadly
diseases. About 45 kinds of mosquitoes live in Virginia, and about a dozen
of them present the same range of threats. Nobody knows how many kinds of
mosquitoes live in the District, because the District has no mosquito
But this year, after a winter 20 percent warmer than usual, and without any
deep cold snap, and a spring twice as wet as normal, people all over the
Washington metropolis may be more mindful of the mosquito than usual. It's
an impressive beast, various and voracious. It can detect the carbon
dioxide exhalations of its prey; it can home in on body heat. In a single
feeding, it can suck blood equal to its own body weight. Its annoying drone
is its mating cry. It is represented by about 3,600 species worldwide. Some
breed in tree holes, others only in rice paddies. Some feed on human blood,
others prefer the canine or bovine variety, others sip flower nectar.
Almost everyone in the United States experiences the mosquito largely as a
pest -- savager of the dewy morn, disturber of the sunset walk, siren in
the tented night -- but the mosquito is also a vector, an agent of disease.
It can put the pest in "pestilence."
It's our backyard nuisance, but it's a global menace.
Malaria is only the best-known of mosquito-borne diseases. It kills about 2
million people a year, and epidemiologists warn that the toll could
increase by as many as a million deaths a year if global warming extends
the range of malaria-bearing species. Of course, the number of Americans
infected with malaria is minuscule -- about 1,200 a year -- and the vast
preponderance of them are infected while traveling abroad. On the other
hand, two cases were reported in New York in 1993, and another one was
reported in Michigan in 1995. They were apparently transmitted by
mosquitoes that had bitten infected people.
Then there's yellow fever, which Walter Reed proved in 1900 is
mosquito-borne. And dengue fever, which is also known as "breakbone fever"
because of the pain it occasions. It swept through Latin America in 1996,
which happens to be the same year that a case was reported in South Texas.
One of the mosquitoes that carries dengue fever -- Aedes aegypti, which
also carries yellow fever -- has moved into the southeastern United States.
No, none of these diseases shows up in any appreciable way in the
But mosquitoes that carry them do.
Among the area's rich biomass are the Aedes aegypti occasionally
(especially if there hasn't been a cold winter for a few years), the
malaria-bearing strain of the Anopheles, and Aedes albopictus, which can
carry both dengue fever and yellow fever. This last is also known as the
Asian tiger mosquito, and it is particularly aggressive and hard to
control. It arrived on American shores in a shipment of used tires from
Japan in 1985. It is now widespread in the South and is showing up
increasingly in Maryland and Virginia. It breeds in still water -- which,
in back yards, means wading pools, birdbaths, flower pots.
"The populations are getting bigger and moving into newer neighborhoods,"
says Joe Kertesz, entomologist for the city of Hampton, Va., and
mid-Atlantic regional director of the American Mosquito Control
Association. "It's one evil and ugly pest, is what it is."
So the area does have its share of, well, vectors. And even if a plague on
the Potomac is in no way imminent, the mosquito is keeping a lot of local
There's a mosquito nursery at the entomology department at the Walter Reed
Army Institute of Research in Northwest Washington. It's chockablock with
water-filled trays speckled with black egg clusters or swimming with larvae
and pupae. Breeding colonies of adults are housed in cages made from the
same white cardboard containers that you see holding half-gallons of ice
The institute has one of the biggest mosquito research facilities in the
world. It needs a dependable supply.
Its mission is to "protect soldiers moving through a sea of disease" on
deployments worldwide, says Lt. Col. Ronald Rosenberg, the entomologist in
charge. Rosenberg draws three interlocking circles on a blackboard in his
small office to help make a point. "You have three different ecologies"
with vector-borne diseases, he says. "The human ecology, the parasite and
the vector. Each of the three has its own life, and the small area where
they intersect is where you get the disease." Usually, the way to go after
the disease is to go after the vector.
Out in the lab, Rosenberg holds up a black plastic container with strip of
insecticide-treated paper clipped to its side. "This is nifty," he says.
One of his staff, research entomologist Michael Perich, has invented a new
way to kill container-breeding mosquitoes -- the kind that lay their eggs
in standing water. The insecticide will probably kill the female when she
lays her eggs in the water-filled container. "And then," Rosenberg says,
"the babies die when they hatch."
This is only one of many insecticides Reed researchers are working on, and
insecticides are only one of their fields of endeavor. They're also
developing mosquito-proof gear (including repellent-treated camouflage
paint), computerized systems that would allow soldiers in the field to
identify local mosquito breeds, and a test that would tell soldiers whether
mosquitoes in a deployment area are carrying the malaria parasite. It works
with a little paper dipstick, like the one you find in a home pregnancy
Downstairs from the nursery, there's a laboratory where mosquitoes are
being fed a warmed-up mix of malaria parasites, serum and red blood cells.
Five infected mosquitoes each will be allowed to feed on the outstretched
arms of volunteers in Food and Drug Administration-approved human trials of
This lab is, of course, secure. Infected mosquitoes are allowed out of
their cages only in an area guarded by double screen doors that open
inward, the better to push would-be escapees back in. "We count the
mosquitoes going in and out, and if it is suspected that a mosquito is
missing, we don't leave until it's found," says Rosenberg. At night, techs
turn on light traps to attract and trap any strays. And when infected
mosquitoes aren't at work in trials, they're held in cages in an insectary
upstairs to which only one person has access.
Over at the Smithsonian Institution's Museum Support Center in Suitland,
there's something called the Walter Reed Biosystematics Unit. The center
doesn't have such a high-security lab, but it does have a
climate-controlled storeroom. It houses the world's largest collection of
mosquito specimens -- roughly 1.5 million little corpses at various stages
of development and from such far-flung quarters as Bangladesh and Thailand
and Brazil and Long Island filling row after row of 29-drawer cabinets.
In a special section, under lock and key, are the holotypes -- the single
specimens that represent their species. Among them is the Anopheles dirus,
a deadly malaria carrier named for the Latin term for "dire." Smithsonian
specialist E.L. Peyton discovered it in Thailand, and he and his colleague
Bruce A. Harrison identified it as a separate species in 1979.
"I love all mosquitoes," Peyton says.
As if to share the love, he asks a colleague to produce a South American
mosquito, Toxorynchites haemorroidalis. And under the microscope, it is
stunning: Its eyes look like copper chain-mail and its sides seem dusted
with silver glitter. Its legs are iridescent, and its tail sports the
blood-red feathery tuft for which it is named. This Toxorynchites doesn't
bite people, but it does eat the larvae of other mosquitoes. It might be a
promising biocontrol agent if it didn't also eat its own.
An Anopheles is likewise striking under the scope. It has gold wings lined
with stripes of deep iridescent purple and blue, decorated with a light
chevron pattern and an iridescent fringe.
"So is that a beauty or not?" Peyton asks.
He and his colleagues practice taxonomy, or the science of classification,
giving names to newly identified species. (Not their own names, though --
the Anopheles peytoni, discovered in Sri Lanka, and Culex peytoni,
discovered in Thailand, were named by others in Peyton's honor.) They also
use their identification skills to track the spread of potentially
dangerous mosquitoes. For instance, they were the first to identify an
Asian tiger mosquito found in the United States.
When they're in the field collecting specimens, they also identify
everything they can about habitat -- latitude and longitude, breeding
environments, anything that will help identify the species. Back in the
center, they develop "keys" -- elaborate descriptions that allow people to
distinguish between mosquito species identified worldwide. One of Peyton's
colleagues, Richard C. Wilkerson, hopes to develop a DNA diagnostic kit,
and unit manager Leopoldo M. Rueda is preparing computerized keys -- keys
that are an adjunct to the ID systems being developed at Walter Reed.
The center is, in fact, funded by Walter Reed. The U.S. military came to
the rescue in the late '80s, when the center's other grants ran out.
"We're the last of the mosquito identifiers still in the business," Peyton
says, somewhat wistfully. "Nobody wants to fund such things anymore."
Meanwhile, the idea of killing mosquitoes -- or at least driving them away
-- can still draw a crowd. DEET, or N,N-Diethyl-m-Toluamide, remains the
mosquito repellent of choice, but it has been around since the 1940s. As
researchers at Walter Reed seek something new -- something beyond Avon's
Skin-So-Soft, which repeated tests have proved ineffective -- so do
scientists at the USDA's Agricultural Research Service. They've tried traps
baited with carbon dioxide or lactic acid. They've tried essential oils
from clove or peppermint or cedarwood. They're trying mosquito-sickening
The search continues.
"Sometimes we forget in our technological world how close we are to these
diseases that ravage the Third World and tropical countries," says Lt. Col.
Rosenberg back at Walter Reed. "It's not simply that we're a colder
country, and it's not simply that we have different geography." Dengue
fever and malaria, he notes, stalk Mexico but rarely appear north of the
border although the vectors are here. "There's nothing magic about the Rio
Grande," he says. The difference is American affluence and the air
conditioning it buys.
That, he says, plus "no place in the world has got mosquito control like
the U.S. does."
After lobbing briquettes into the hollow at Newbridge, Jeannine Dorothy and
Pat Ferrao have lunch and then park by the side of a road in Bowie. They
cut across a grassy field, though a blackberry thicket and a woods to reach
another flooded hollow. In some places, the water is two feet deep. A
drowned snake is soaking in it, as is a beaver-felled tree. "I've never
seen it this wet," Dorothy says.
The mosquitoes here are close enough to maturity that the growth regulator
won't do. So Dorothy takes the nozzle from a sprayer she's wearing on her
back and starts spraying bonide oil over the water. It's a mineral oil
mixed with an agent that spreads it rapidly over water. In about 20
minutes, it should effectively drown the mosquitoes.
Later, Dorothy ends her day dipping larvae out of a ditch along a dead-end
road in Severn Crossing. That evening, she'll carry a glass jar full of
them with her when she speaks to the University Park town council about the
need for mosquito control.
Driving back to her office in College Park, she talks about one of the
minor hazards of her occupation. "You start to notice water everywhere,"
she says. Even on vacation, she finds herself musing, "I wonder if that
Martha M. Hamilton is a writer for The Post's Business section.
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