Desert 'tropics' breed mosquitoes, danger
Reprinted from:
The Arizona Republic
By: Judy Nichols
First came the people. Then the water. Ten the grasses and date
palms and orange trees.
They created a Garden of Eden, a tropical paradise if the desert. And
they saw it was good. Especially for mosquitoes.
This tropicalization of the valley , with increased humidity and more
sources of standing water, has created an environment where mosquitoes can
spread Malaria, West Nile virus and dengue fever.
Last week, mosquitoes tested positive for the West Nile virus in Wilcox,
in eastern Arizona, and a horse on the Navajo Reservation in the northeastern
corner of the state was found to have the disease.
The virus, which can cause encephalitis, or swelling of the brain and
spinal cord, has been moving toward Arizona from the east since 1999.
Dengue fever, a tropical disease that can cause fatal hemorrhaging, has
been found in Texas and Mexico, making the entire southwest a risk area.
The diseases are carried by infected birds to other animals and people
by female mosquitoes, which need blood for their eggs to mature. Males
don't bite.
When the female bites an infected bird, she becomes infected herself.
That infection spreads to her salivary glands and is passed on when
she bites her next mammal.
Water everywhere
Water , essential for mosquitoes, is everywhere in the valley, from swimming
pools to man-made lakes, backyard fountains to golf hazards. Restored
wetlands, canals and flood irrigation. And sprinklers. And misters.
In the early 1900's when Arizona's rivers flowed freely, unencumbered
by dams, there were mosquitoes.
"They were mainly along the rivers, especially the confluence of two rivers,
which was where most of the settlements forts and trading post were," said
Craig Levy, program manager for vector born diseases at the Arizona Department
of Health Services.
The mosquitoes back then were of the genus anopheles, and they carried
Malaria, infecting the settlers, soldiers and Native Americans.
But away from the rivers, where the area was a true desert, no mosquitoes.
When the rivers were dammed, and the valley became drier, mosquitoes
thinned and the potential for Malaria declined, although the anopheles mosquitoes
never died out completely.
They have been joined by the culex which can transmit West Nile virus
and other encephalitic diseases, and the newest bug on the block,
the Aedes aegypti, which can carry dengue and yellow fevers.
"The Aedes aegypti is a tropical mosquito that
is thriving in the Arizona deserts," Levy said. " It requires
increased humidity. If we did not create a tropical environment, it
could be not possibly survive."
"With all of the development and introduction
of vegetation, we have taken what used to be desert and created a subtropical
paradise."
Most of the paradise is in the backyards.
"When we were first trying to identify the areas in Tempe where
the Aedes aegypti was breeding, we found yards that looked like they were
in Jamaica or Panama." said John Townsend, vector control manager for Maricopa
County. "It feels like you're in a jungle. There's a swimming
pool, waterfall, banana trees, bamboo."
A little Oaisis
The valley has historically touted lush resorts like the Arizona Biltmore,
said Susanna Smith, a landscape designer for 23 years.
"It's a natural reaction to the heat , " Smith said. "People want
some sort of refuge."
So they plant palm trees, hibiscus, Natal plum, society garlic, cape honeysuckle
and plumbago. And they put in fountains and fish ponds.
"Most everybody wants a little oasis, maybe by their
patio in the back or private little garden," Smith said.
But she warns them to chlorinate their water or put fish into the fountains
to eat mosquito larvae.
" I have a fish pond, and I've been bitten by a mosquito," she said.
Toony Brazel, a climatolpgist and professor of geography at Arizona
State University, said backyard micro climates are very easy to create.
"If you have a protected yard with a fence or wall, some trees to protect
from dehydrationing winds and you water if to death, you can quite substantially
change the
microlimate," Brazel said.
Another contributing factor for tropical bugs may be warmer temperatures
and fewer frosts because of the urban heat island and global warming, both
areas Brazel has studied.
"No freezes allow tropical things to survive," he said.
Night time lows in the valley have increased an average 10 degrees since
the 1940s, staying in the 80s in July . The
mean temperature has increased about 6 degrees to the high 70s over the past
100 years.
The ideal birthplace for mosquitoes is stagnant water that stands
for several days. Especially if there are small plants or grass
that eggs can nestle under.
Moving water or open bodies that have even a little wave action from breezes
don't allow eggs to hatch. The eggs need oxygen and have small straw
like openings to let the larvae breathe. Any water movement will drown
them.
Things really get good for mosquitoes when backyards are neglected.
Fountains, which are fine when they are running or bubbling, become
incubators when they're turned off..
Standing water in buckets , coolers, cans or tires can hatch thousands
of mosquitoes.
Poorly maintained swimming pools become major mosquito breeding factories.
Be careful. The mosquitoes you hatch will look for you first.
Mosquitoes have been tracked miles from their breeding sites, but if they
find a blood source, they stay in the vicinity.
"Our saying is, 'you breed feed' em," Townsend said.
"They will find the first warm-blooded mammal and take a blood meal
from them."
So officials preach vigilance. Get rid of backyard clutter that holds
standing water. Maintain your pool.
If a vacant house has a green pool, Townsend said the county might put
gambusia fish in it.
"Within a few months, there will be several hundred fish," he said. "The
pool will still be green and nasty, but there won't be any mosquitoes."
They put pesticide in bodies of water to kill larvae. they spray
with malathion or synthetic pyrethum to kill adults.
Irrigation canals are not a problem because the water is moving, and irrigation
in yards or fields is fine if it soaks in within 48 hours. But in
places where there is caliche, or clay like soil, or where horses or cows
have compacted the ground, the water sometimes stands longer.
Restored wetlands also can cause problems.
"If they're designed and maintained properly, they're fine," Levy said.
"Otherwise they become mosquitoe-breeding nightmares because they also
attract the birds, which are the virus reservoirs."
Health officials carefully watch for signs of disease.
They investigate hospital reports of encephalitis symptoms, check horses
with signs of neurological problems, test dead birds, take blood samples
from flocks of chickens across the state, amd trap and test mosquitoes.
At 7 a.m last Friday, Dan Ramire of the county vector control, picked up
a mosquito trap that had been out overnight near the Water Ranch at Greenfield
and Guadalupe roads in Gilbert.
The County regularly gets complaints in this area, mostly because of over
irrigation that stands too long on small farms nearby, Ramirez said.
The trap holds dry ice to emit carbon dioxide and attracts mosquitoes fooled
into thinking it is someone's or somethings breath. It was out for
16 hours.
"There are thousands of mosquitoes here, an extreme haul," Ramirez said.
Gaurd against mosquitoes
When outside, apply insect repellent containing DEET
on skin and clothing.
Cover exposed skin with clothing: Light colors help you spot mosquitoes
better.
Be aware of peak mosquito hours, evening and early morning.
Drain standing water: birdbaths, pets' water dishes, plants wading pools.
Install or repair screens on doors and windows.
Place mosquito netting over infant carriers.