West Nile Virus and Wildlife

This pamphlet summarizes the latest information on the
virus at the time of writing. As with any medical subject,
For more nature habitat information however, information changes frequently, based on the
results of new research or changes in the virus itself.
Visit these helpful websites:

A Plant's Home With this in mind, you are encouraged to read this
A Bird's Home pamphlet, but also to visit the web sites which are
A Homesteader's Home listed, or to call your local Health Department,
in order to get the very latest updates.

West Nile Virus
and Wildlife
Usually when we complain about is fairly common in Africa, West
"problem wildlife," we’re talking Asia, and the Middle East. The
about annoyances: deer nibbling first outbreak in this country in
our shrubs; squirrels devouring our New York City in 1999 seems to be
tulip bulbs; raccoons raiding our related to a strain that appeared
trash cans. in Israel the previous year.

Generally we try advice from At this point, experts consider
friends and authorities, and either it to now be permanently
solve the problem or come to some established in the Western
kind of tolerance and Hemisphere and, depending on
accommodation. the local climate, it can be
overwintered or transmitted all
Sometimes, however, much more year around.
serious concerns also tie into our
love of wild creatures. In recent As Paul Epstein of Harvard
years, one of the most frightening Medical School’s Center for Health
of these has been the spread of and the Global Environment
West Nile Virus (WNV). explained in Scientific American ,
global warming has contributed to
Learning that it is present in conditions that favor diseases like
wild bird populations, and now WNV. Mild winters allow its survival
appears to be spreading to into the spring, giving it an earlier
mammals, can make us wonder if start in the year, while drought
our fondness for wildlife and our kills insect predators such as
attempts to enhance wildlife ladybugs and lacewings.
habitat are actually putting our
own health and that of our Drought also causes birds and
families at risk. mosquitoes to congregate in
larger numbers at smaller and
Somewhat surprisingly, we don’t fewer water sources, increasing
know the exact origin of the the likelihood of spreading the
specific virus that has reached virus, while higher temperatures
the United States, although WNV cause an increase in mosquito

© WindStar Wildlife Institute Page 1 A Plant's Home

activity, which means faster Most birds and animals which biting another animal in the same
reproduction and maturation of are infected will survive. That being vicinity. For this reason certain
the virus, and a greater number of said, the virus is expanding within habitat elements, such as bird
potential bites. many wildlife populations, and can feeders, should be more numerous
be expected to affect greater and placed farther apart than you
Of all the types of mosquitoes, numbers in the future. might normally have planned.
the one in the United States which
is the most common carrier of It is also spreading surprisingly At this time, indications are
WNV is Culex pipiens. It is most quickly throughout the country, that the originally-infected animal
prevalent in urban environments, found now in nearly every state, is only infectious (through
rather than in healthy wetlands just over three years after its mosquito transmission) for a few
and wild areas. It is the female first appearance in NY. days. Birds are considered
mosquito that does the biting, “reservoir" hosts, since an infected
needing the protein in blood to The fact that WNV is not host- bird can transfer the virus to
ensure proper development of her specific is of great concern. Even many mosquitoes.
eggs. exotic wildlife in zoos is being
affected, putting breeding Interestingly, humans and some
When the insect bites an programs in jeopardy. other mammals, such as deer, are
infected animal, the virus is stored called “dead end" hosts. This
in the mosquito’s salivary glands, In natural areas where certain means that the virus doesn’t stay
and then can be transmitted to species are hit hard by the virus, viable in their bodies long enough
the next "host" that is bitten. the balance of nature can shift. for them to transfer it to a lot of
For example, rodents can other mosquitoes.
Mosquito eggs are laid in proliferate if the number of
bunches, and each bunch can raptors drops. For some reason, while some
contain hundreds of eggs, so it’s dead end hosts (such as humans
easy to see why they can multiply As native wildlife is stressed and horses) can get sick, others
quickly. In addition, the eggs can more and more by other factors, (like dogs and cats) can be
be dormant for years if there is a such as habitat destruction, infected but won’t become ill.
drought, then hatch when water drought, and pesticide use, it is
returns. more important than ever that we An infected animal or bird can
replace lost habitat and become serve as a valuable warning
It is important to remember, educated on what can be done to system to people, indicating that
however, that even in places where attract and help wildlife without there are infected mosquitoes in
the disease has been confirmed, endangering ourselves or our the area, and that precautions
it is actually carried by a very low families.. should be taken to avoid getting
percentage of the mosquitoes in bitten.
that area. There are no documented cases
of a person getting WNV from While there is no evidence that a
At one time crows seemed to be another person or from an person can be infected by handling
both the primary sources and animal. This is an important wildlife, whether it is alive or dead,
victims of WNV. Now, however, more distinction for those who care for that has WNV, it is a reasonable
than 140 species of birds have animals, whether wild or precaution to wear gloves when
been reported, as well many other domestic. doing so, and to avoid getting any
creatures including horses, cats, blood from a suspected infected
dogs, chipmunks, skunks, bats, Although there is evidence that animal on an open wound.
squirrels, bears, alligators, and birds can now pass the virus
domestic rabbits. directly to other birds, most There is also no evidence that a
animals don’t seem to transmit person can contract the virus by
At this time, many areas still the virus to other animals, so eating an infected bird or animal,
request that dead birds be having an infected pet in contact but it is prudent to be sure that
reported to the local health with other pets, or encouraging the meat is well-cooked before
department. However, these birds groups of wildlife to congregate, being consumed.
might not be physically collected doesn’t directly encourage the
by authorities in that jurisdiction spread of the disease. It is very important to
if the presence of WNV has already emphasize the low risk to humans.
been established, since further The main danger is that a Most people who are infected with
testing would not yield any mosquito will bite the infected WNV will not actually have any
additional useful information. animal and then spread WNV by symptoms.


In those few cases where the available at the time of this a threat to the environment.
disease is present, symptoms writing. However, they are highly toxic to
appear 3 to 14 days after being bees and aquatic life, so any
bitten. Only about 20 percent of Often the first reaction of benefits are not without serious
those affected will have the typical communities faced with evidence drawbacks.
fever, headache, flu-like body of WNV is to call for chemical
aches, and perhaps a rash and spraying of neighborhoods and Any adulticide product will kill
swollen lymph glands. These mild wetlands. This process can all insects indiscriminately. Not
forms of the virus usually last just change the natural environment, only does this lower the
a few days. actually making it more population of beneficial insects,
hospitable to mosquitoes by but it also cuts down on the
There is some evidence that the killing predators (such as fish, food supply for both local and
virus can be transmitted through other insects, and birds). migratory insect-eating bird
breast milk, but there are no species.
reports of any infants infected in In addition, most insecticides
this way showing serious have been designed for agricultural Larvicides tend to be more
symptoms, and the benefits of use, and have not been tested or effective in controlling mosquito
breast-feeding are felt to outweigh evaluated for repeated contact populations than adulticides.
any possible risks. with humans. They can be applied selectively, in
more controlled conditions. They
Overall, children less than one- A further concern is the speed include both natural bacteria and
year-old are rarely infected by the at which insects reproduce, giving chemicals. Some of the more
virus. There is no evidence that them the ability to build up a common ones are microbial Bti,
WNV can be transmitted through resistance to an insecticide far which kills the larvae when they
pregnancy or birth. more rapidly than larger ingest it, and surface oils which
predators. Some of these, such as are spread on top of water to
Of those adults who do have bats, may actually die out in an suffocate eggs, larvae, and
symptoms, less than one percent area before they can build up a pupae.
will become seriously ill. Those over tolerance, while the newly-adapted
50 years of age, or with mosquitoes will keep on Although safer than
compromised immune systems multiplying. adulticides, larvicides can be
from other causes, are the most highly toxic to aquatic life,
at risk for more serious cases of There are two kinds of pesticides including amphibians, insects,
the disease. These more severe used: adulticides, which target the and fish, and in high doses can
symptoms (including high fever, mature mosquitoes, and larvicides, cause serious reactions in
stiff neck, disorientation, and which are aimed at the eggs and humans.
tremors) can last several weeks. larvae. Adulticides are the less
efficient and potentially the more Reducing the number of
At this time it is assumed that dangerous of the two. mosquitoes is obviously the best
anyone infected with WNV will way to lower the chances of being
acquire lifelong immunity. Some communities spray with bitten, but there are many
malathion, an organophosphate. precautions that people can take
There have been some reports Organophosphates are known to which pose no danger to wildlife
about possible transmission of be nerve toxins, and as such need or the environment. Basic home
WNV through blood transfusions to be used with extreme caution maintenance is important,
or organ transplants. This is being since the results of long-term including making sure that there
studied carefully, and physicians human exposure are not yet known. are screens on windows and
and blood banks are now aware of doors, and that these screens
the issue and are being as careful Other commonly-used are free from holes that would
as possible. adulticides are based on allow the insects to enter.
pyrethroids, which are derived from
It is important to remember the flowers of the pyrethrum In the yard, watch for any
that donating blood poses no risk plants (such as containers that could retain
to the donor, and that it is critical chrysanthemums) or a synthetic standing water, even in very small
that the nation’s blood supply be equivalent. amounts. These might include old
kept at safe levels. Several
companies are working to develop Pyrethroids break down quickly, tires, flower pots, clogged
screening tests, vaccinations, and especially in sunlight, and they gutters, pool covers, even
treatments, but nothing is yet bind to the soil so they are less of children’s toys.


Eliminate these, or empty them Concentrations vary from been no reported cases of
frequently, at least every couple product to product. According to negative reactions to DEET in
of days. Drill holes in the bottom the Centers for Disease Control, a pregnant or nursing mothers.
of larger containers, such as product containing 23.8 percent
those used for recycling, if they DEET provides five hours of There is a lot of research going
are kept outside. Turn over protection, while 6.65 percent on now in an attempt to develop
wheelbarrows and buckets. protects for two hours. plant-based repellents which
would be non-toxic.
You should wear light-colored If you are concerned about any
long-sleeved shirts and long negative effects from DEET, you Catnip is showing a lot of
can apply concentrations promise. Although no one yet
pants when outdoors during the
appropriate for the amount of knows why it works, the
day. Dark clothing attracts the
time that you expect to be nepetalactone which gives the
insects because it looks like a outdoors, then reapply if plant its scent appears to be even
cool, shadowy area. Put mosquito necessary. more effective than DEET.
netting over baby-carriers, and
avoid being out at dawn and dusk, There have been numerous Anecdotal evidence from
when mosquitoes bite the most studies on the safety of DEET, individuals suggests possible
frequently. and it appears to cause only rare repellent capabilities from cedar
negative reactions in sensitive oil, rubbing alcohol, Vaporub, Avon
Not all species of mosquitoes people. All the same, you Skin-So-Soft, vanilla, eucalyptus
are attracted to light, so light shouldn’t use a higher oil, and lavender, to name just a
traps are not effective, and concentration than you need, and few. Since the purpose is mainly to
usually end up killing many more it’s important to apply it as cover up your own scent and not
beneficial insects than harmful directed. attract the mosquitoes, there are
ones. plenty of possibilities for
Don’t put the repellent on open experimentation.
In one study, of the 10,000 or irritated skin, or on skin that
bugs killed by a “bug zapper," only will be covered with clothing. You Rather than increasing our risk
eight were mosquitoes. Other should spray the clothing itself, of exposure to West Nile Virus by
tests produced similar results, and then wash it before wearing it attracting wildlife to our yards,
killing far more beneficial insects again. enhancing our backyard habitat
and mosquito predators than to attract mosquito predators
mosquitoes themselves. You don’t need to apply DEET in and remove favorable conditions
large amounts in order to get full for mosquito reproduction is one
Many people turn to insect protection, and you should wash of the best ways to reduce our
repellents for protection. any treated skin once you come risk of infection.
Mosquitoes find their victims by back indoors.
smell, either from the scent of Lowering the number of
the skin, or the odor of exhaled If using spray repellent, avoid mosquitoes is obviously the best
carbon dioxide. Insect repellents getting it in your eyes or mouth by way to lower the chances of being
don’t kill mosquitoes, they just spraying it on your hands and then bitten.
cover the odors which would rubbing it on your face and neck.
normally attract them, rendering This could include providing an
us somewhat “invisible." Although no serious illnesses environment which appeals to
have been reported in children, insect-eating birds by installing
cautious experts advise using bluebird nesting boxes, landscaping
The most effective repellent on
lower concentrations (10 percent with native plants which attract
the market seems to be DEET (N,
or less) of DEET on those from 2 other insects (both as mosquito
N-diethyl-m-toluamide). Higher
to 12 years old, while others even predators and as food for birds),
percentages of DEET within a and providing water sources.
approve it for infants over two
repellent means that the
months old.
protection will last longer, but it If you have a suitable location to
won’t be any more directly It is better for adults to put attract purple martins, they will
effective in repelling the insects, repellent on their own hands, and consume some mosquitoes, but
and a concentration of more than then apply it to children. Avoid unfortunately they aren’t very
50 percent doesn’t continue to putting it on the hands of young effective at reducing the
increase the length of protection children, since their hands usually population of that particular
time. end up in their mouths. There have insect.


Mosquitoes are most active in Larger bodies of water such as Pupae are rounder and have a
the early morning and late ponds, even if they don’t include a rolling motion.
evening, in low vegetation, while waterfall or other source of
purple martins feed during the movement, will encourage the If you determine that you do
day, high in the sky. Having purple presence of frogs and other have a mosquito presence, in
martins on your property offers creatures which happily eat addition to following all of the
many other rewards, but don’t mosquito eggs and larvae, as will above practices, you might want
count on them to control any fish that you include. to add a “mosquito dunk," which
mosquitoes. is a commonly-available donut-
Female mosquitoes look for shaped concentration of Bti
The situation is similar when it sheltered spots to lay their eggs, (Bacillus thruingiensis
comes to bats. Depending on so don’t create “trapped" water, israelensis). It will kill mosquito
where you live, and the species such as between rocks, in gravel, larvae (but not eggs or pupae)
that inhabit the area, bats may or in very shallow (less than 6") without harming birds or fish or
eat a significant number of areas. other wildlife. These are also
mosquitoes, but their primary diet appropriate for birdbaths which
is moths and beetles. Avoid plants with leaves that don’t have moving water.
hang over the edges of the pond,
The little brown bat seems to since they will provide protection If reading all of the above
be the most voracious consumer from predators. The tops of precautions still leaves you
of mosquitoes, especially in potted plants can provide nervous, it is important to
urban areas, so it can be suitable egg-laying areas if they remember that humans are not
worthwhile to install bat houses extend out of the water, so keep very good hosts for West Nile
and try to attract them. As with them submerged. Virus, and that only a small
purple martins, bats provide percentage of people will
many other benefits, so Pond sides should be steep, become ill even if they happen
providing suitable habitat for and provision should be made for to get bitten by an infected
future draining of the water if mosquito.
them is definitely worthwhile for
reasons other than the control needed. If you incorporate a
The toll is greater on wildlife,
of West Nile Virus. waterfall, avoid designing it with but it is thought that, as in
small pools that will hold calm countries where WNV has been
Mosquitoes can only reproduce water. common for many years, most
when there is water available, but species will develop a resistance
getting rid of birdbaths and ponds Fish are wonderful mosquito to it through the process of
on your property is not a good predators, so allow sufficient natural selection.
step to take. All wildlife needs depth in your pond to stock it.
water, and it is becoming more Remove excessive organic In the meantime, as we deal
and more limited, whether due to material, such as leaves or with its spread in this country,
development, the filling in of flowers, since it can decay and kill the answer to the problem isn’t
wetlands, or drought conditions. off the fish. to spray indiscriminately, or to
use chemicals that can put us
As long as proper precautions Don’t overfeed your fish, and at potentially greater risk and
are followed, providing water thin aquatic plants enough to harm wildlife and the
sources will encourage wildlife, allow the fish to swim easily environment.
including mosquito predators, throughout the pond. Be aware
without raising the risk of that frog eggs are also tasty The best thing that we can
contracting West Nile Virus. fish food, so if you want to do is replace or enhance wildlife
encourage amphibians to multiply habitat to keep it healthy, and
While standing water can harbor you will need to have a section of encourage populations of
mosquito larvae, the water that is your pond inaccessible to the mosquito predators.
preferred by birds and other fish.
wildlife is changed and freshened As you build ponds to attract
frequently, and, even better, may Visual inspection will allow you dragonflies and frogs, plant
be kept in motion with a drip or to detect mosquito larvae in the native shrubs to feed birds, and
small fountain system. Moving water. This will be easier if you curb your use of pesticides so
water does not attract collect a sample in a white that predatory insects can
mosquitoes. Standard bird baths container, which makes the larvae thrive, you will not only be helping
should be filled with fresh water show up better. They will swim in wildlife, but you will be protecting
every one to two days. a wiggling, sideways manner. yourself and your family.


RESOURCES
For further reading and the latest information, call your local health
department or try these online resources:
s Centers for Disease Control West Nile web site:
http://www.cdc.gov/ncidod/dvbid/westnile/index.htm
s Information on mosquito prevention and control when building a pond:
http://www.mosquitoes.org/Publicinfo/fpconst.html
s West Nile Virus environmental issues:
http://www.des.state.nh.us/factsheets/co/co-12.htm
s Overview of history and the virus itself, geared towards teaching:
http://www.riverdeep.net/current/2000/08/
082500_westnile_arc.jhtml
s Steps to take to minimize risk of being bitten/infected:
http://www.ehs.cornell.edu/bio/WestNileVirus.htm
s Extensive information on history, transmission, symptoms, repellents:
http://www.continuingeducation.com/pharmacy/westnile/index.html
s Good set of Frequently Asked Questions:
http://www.metrokc.gov/health/westnile/
s Answers to questions related to feeding birds:
http://www.birdwatchers.com/WestNile.html
s American Bird Conservancy view on West Nile and pesticide use:
http://www.abcbirds.org/pesticides/west_nile_position_statement.htm
s North American Butterfly Association on the effects of pesticides on
other insects:
http://www.naba.org/wnvirus.html://www.naba.org/wnvirus.html
s Click on “Search" and enter “West Nile Virus" for two articles from the
Environmental Research Foundation about pesticide use:
http://www.rachel.org/home_eng.htm
This article was written by
s Purple Martin facts, including why they aren’t good for mosquito control: Maryland Master Wildlife
http://www.purplemartin.org/update/ThirtWays.html Habitat Naturalist Cathy
Discusses bat control of mosquitoes: Gilleland.
s
http://www.texasmosquito.org/Bats.html For more information or for the
s History of methods of mosquito control: name of a Master Wildlife
http://www.ces.ncsu.edu/onslow/staff/drashash/newsletr/ Habitat Naturalist in your area,
Jul2001.html please contact:

s Non-chemical mosquito control using Integrated Pest Management WindStar Wildlife Institute
methods:
http://www.colostate.edu/Depts/IPM/natparks/mosquito.html E-mail: wildlife@windstar.org
s Article on using catnip to repel mosquitoes: http://www.windstar.org
http://www.sciencedaily.com/releases/2001/08/010828075659.htm
s Suggestions for homemade insect repellents: WindStar Wildlife Institute is a
http://www.sciencedaily.com/releases/2001/08/010828075659.htm national, non-profit
conservation organization
s EPA in-depth information on lavicides: whose mission is to help
http://www.epa.gov/pesticides/citizens/larvicides4mosquitos.htm individuals and families
establish or improve the wildlife
s National Pesticide Information Center: habitat on their properties.
http://npic.orst.edu/wnv/


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West Nile Virus and Wildlife