West Nile Virus and Wildlife by Stephen McCarthy

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This pamphlet summarizes the latest information on the virus at the time of writing. As with any medical subject, however, information changes frequently, based on the results of new research or changes in the virus itself. With this in mind, you are encouraged to read this pamphlet, but also to visit the web sites which are 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 "problem wildlife," we’re talking about annoyances: deer nibbling our shrubs; squirrels devouring our tulip bulbs; raccoons raiding our trash cans.

is fairly common in Africa, West Asia, and the Middle East. The first outbreak in this country in New York City in 1999 seems to be related to a strain that appeared in Israel the previous year.

Generally we try advice from friends and authorities, and either solve the problem or come to some kind of tolerance and accommodation.

At this point, experts consider it to now be permanently established in the Western Hemisphere and, depending on the local climate, it can be overwintered or transmitted all year around.

Sometimes, however, much more serious concerns also tie into our love of wild creatures. In recent years, one of the most frightening of these has been the spread of West Nile Virus (WNV). Learning that it is present in wild bird populations, and now appears to be spreading to mammals, can make us wonder if our fondness for wildlife and our attempts to enhance wildlife habitat are actually putting our own health and that of our families at risk. Somewhat surprisingly, we don’t know the exact origin of the specific virus that has reached the United States, although WNV

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As Paul Epstein of Harvard Medical School’s Center for Health and the Global Environment explained in Scientific American, global warming has contributed to conditions that favor diseases like WNV. Mild winters allow its survival into the spring, giving it an earlier start in the year, while drought kills insect predators such as ladybugs and lacewings. Drought also causes birds and mosquitoes to congregate in larger numbers at smaller and fewer water sources, increasing the likelihood of spreading the virus, while higher temperatures cause an increase in mosquito

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activity, which means faster reproduction and maturation of the virus, and a greater number of potential bites. Of all the types of mosquitoes, the one in the United States which is the most common carrier of WNV is Culex pipiens. It is most prevalent in urban environments, rather than in healthy wetlands and wild areas. It is the female mosquito that does the biting, needing the protein in blood to ensure proper development of her eggs. When the insect bites an infected animal, the virus is stored in the mosquito’s salivary glands, and then can be transmitted to the next "host" that is bitten. Mosquito eggs are laid in bunches, and each bunch can contain hundreds of eggs, so it’s easy to see why they can multiply quickly. In addition, the eggs can be dormant for years if there is a drought, then hatch when water returns.

Most birds and animals which are infected will survive. That being said, the virus is expanding within many wildlife populations, and can be expected to affect greater numbers in the future.

biting another animal in the same vicinity. For this reason certain habitat elements, such as bird feeders, should be more numerous and placed farther apart than you might normally have planned.

It is also spreading surprisingly quickly throughout the country, found now in nearly every state, just over three years after its first appearance in NY.

At this time, indications are that the originally-infected animal is only infectious (through mosquito transmission) for a few days. Birds are considered “reservoir" hosts, since an infected bird can transfer the virus to many mosquitoes.

The fact that WNV is not hostspecific is of great concern. Even exotic wildlife in zoos is being affected, putting breeding programs in jeopardy. In natural areas where certain species are hit hard by the virus, the balance of nature can shift. For example, rodents can proliferate if the number of raptors drops.

As native wildlife is stressed more and more by other factors, such as habitat destruction, drought, and pesticide use, it is more important than ever that we replace lost habitat and become educated on what can be done to It is important to remember, however, that even in places where attract and help wildlife without endangering ourselves or our the disease has been confirmed, families.. it is actually carried by a very low percentage of the mosquitoes in that area. There are no documented cases of a person getting WNV from At one time crows seemed to be another person or from an both the primary sources and animal. This is an important victims of WNV. Now, however, more distinction for those who care for than 140 species of birds have animals, whether wild or been reported, as well many other domestic. creatures including horses, cats, dogs, chipmunks, skunks, bats, Although there is evidence that squirrels, bears, alligators, and birds can now pass the virus domestic rabbits. directly to other birds, most animals don’t seem to transmit At this time, many areas still the virus to other animals, so request that dead birds be having an infected pet in contact reported to the local health with other pets, or encouraging department. However, these birds groups of wildlife to congregate, might not be physically collected doesn’t directly encourage the by authorities in that jurisdiction spread of the disease. if the presence of WNV has already been established, since further The main danger is that a testing would not yield any mosquito will bite the infected additional useful information. animal and then spread WNV by

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Interestingly, humans and some other mammals, such as deer, are called “dead end" hosts. This means that the virus doesn’t stay viable in their bodies long enough for them to transfer it to a lot of other mosquitoes. For some reason, while some dead end hosts (such as humans and horses) can get sick, others (like dogs and cats) can be infected but won’t become ill. An infected animal or bird can serve as a valuable warning system to people, indicating that there are infected mosquitoes in the area, and that precautions should be taken to avoid getting bitten. While there is no evidence that a person can be infected by handling wildlife, whether it is alive or dead, that has WNV, it is a reasonable precaution to wear gloves when doing so, and to avoid getting any blood from a suspected infected animal on an open wound. There is also no evidence that a person can contract the virus by eating an infected bird or animal, but it is prudent to be sure that the meat is well-cooked before being consumed. It is very important to emphasize the low risk to humans. Most people who are infected with WNV will not actually have any symptoms.

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In those few cases where the disease is present, symptoms appear 3 to 14 days after being bitten. Only about 20 percent of those affected will have the typical fever, headache, flu-like body aches, and perhaps a rash and swollen lymph glands. These mild forms of the virus usually last just a few days. There is some evidence that the virus can be transmitted through breast milk, but there are no reports of any infants infected in this way showing serious symptoms, and the benefits of breast-feeding are felt to outweigh any possible risks. Overall, children less than oneyear-old are rarely infected by the virus. There is no evidence that WNV can be transmitted through pregnancy or birth. Of those adults who do have symptoms, less than one percent will become seriously ill. Those over 50 years of age, or with compromised immune systems from other causes, are the most at risk for more serious cases of the disease. These more severe symptoms (including high fever, stiff neck, disorientation, and tremors) can last several weeks. At this time it is assumed that anyone infected with WNV will acquire lifelong immunity. There have been some reports about possible transmission of WNV through blood transfusions or organ transplants. This is being studied carefully, and physicians and blood banks are now aware of the issue and are being as careful as possible. It is important to remember that donating blood poses no risk to the donor, and that it is critical that the nation’s blood supply be kept at safe levels. Several companies are working to develop screening tests, vaccinations, and treatments, but nothing is yet

available at the time of this writing. Often the first reaction of communities faced with evidence of WNV is to call for chemical spraying of neighborhoods and wetlands. This process can change the natural environment, actually making it more hospitable to mosquitoes by killing predators (such as fish, other insects, and birds). In addition, most insecticides have been designed for agricultural use, and have not been tested or evaluated for repeated contact with humans. A further concern is the speed at which insects reproduce, giving them the ability to build up a resistance to an insecticide far more rapidly than larger predators. Some of these, such as bats, may actually die out in an area before they can build up a tolerance, while the newly-adapted mosquitoes will keep on multiplying. There are two kinds of pesticides used: adulticides, which target the mature mosquitoes, and larvicides, which are aimed at the eggs and larvae. Adulticides are the less efficient and potentially the more dangerous of the two. Some communities spray with malathion, an organophosphate. Organophosphates are known to be nerve toxins, and as such need to be used with extreme caution since the results of long-term human exposure are not yet known. Other commonly-used adulticides are based on pyrethroids, which are derived from the flowers of the pyrethrum plants (such as chrysanthemums) or a synthetic equivalent. Pyrethroids break down quickly, especially in sunlight, and they bind to the soil so they are less of

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a threat to the environment. However, they are highly toxic to bees and aquatic life, so any benefits are not without serious drawbacks. Any adulticide product will kill all insects indiscriminately. Not only does this lower the population of beneficial insects, but it also cuts down on the food supply for both local and migratory insect-eating bird species. Larvicides tend to be more effective in controlling mosquito populations than adulticides. They can be applied selectively, in more controlled conditions. They include both natural bacteria and chemicals. Some of the more common ones are microbial Bti, which kills the larvae when they ingest it, and surface oils which are spread on top of water to suffocate eggs, larvae, and pupae. Although safer than adulticides, larvicides can be highly toxic to aquatic life, including amphibians, insects, and fish, and in high doses can cause serious reactions in humans. Reducing the number of mosquitoes is obviously the best way to lower the chances of being bitten, but there are many precautions that people can take which pose no danger to wildlife or the environment. Basic home maintenance is important, including making sure that there are screens on windows and doors, and that these screens are free from holes that would allow the insects to enter. In the yard, watch for any containers that could retain standing water, even in very small amounts. These might include old tires, flower pots, clogged gutters, pool covers, even children’s toys.

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Eliminate these, or empty them frequently, at least every couple of days. Drill holes in the bottom of larger containers, such as those used for recycling, if they are kept outside. Turn over wheelbarrows and buckets.

Concentrations vary from product to product. According to the Centers for Disease Control, a product containing 23.8 percent DEET provides five hours of protection, while 6.65 percent protects for two hours.

You should wear light-colored long-sleeved shirts and long pants when outdoors during the day. Dark clothing attracts the insects because it looks like a cool, shadowy area. Put mosquito netting over baby-carriers, and avoid being out at dawn and dusk, when mosquitoes bite the most frequently.

If you are concerned about any negative effects from DEET, you can apply concentrations appropriate for the amount of time that you expect to be outdoors, then reapply if necessary.

Not all species of mosquitoes are attracted to light, so light traps are not effective, and usually end up killing many more beneficial insects than harmful ones. In one study, of the 10,000 bugs killed by a “bug zapper," only eight were mosquitoes. Other tests produced similar results, killing far more beneficial insects and mosquito predators than mosquitoes themselves. Many people turn to insect repellents for protection. Mosquitoes find their victims by smell, either from the scent of the skin, or the odor of exhaled carbon dioxide. Insect repellents don’t kill mosquitoes, they just cover the odors which would normally attract them, rendering us somewhat “invisible." The most effective repellent on the market seems to be DEET (N, N-diethyl-m-toluamide). Higher percentages of DEET within a repellent means that the protection will last longer, but it won’t be any more directly effective in repelling the insects, and a concentration of more than 50 percent doesn’t continue to increase the length of protection time.

There have been numerous studies on the safety of DEET, and it appears to cause only rare negative reactions in sensitive people. All the same, you shouldn’t use a higher concentration than you need, and it’s important to apply it as directed. Don’t put the repellent on open or irritated skin, or on skin that will be covered with clothing. You should spray the clothing itself, and then wash it before wearing it again. You don’t need to apply DEET in large amounts in order to get full protection, and you should wash any treated skin once you come back indoors. If using spray repellent, avoid getting it in your eyes or mouth by spraying it on your hands and then rubbing it on your face and neck. Although no serious illnesses have been reported in children, cautious experts advise using lower concentrations (10 percent or less) of DEET on those from 2 to 12 years old, while others even approve it for infants over two months old. It is better for adults to put repellent on their own hands, and then apply it to children. Avoid putting it on the hands of young children, since their hands usually end up in their mouths. There have

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been no reported cases of negative reactions to DEET in pregnant or nursing mothers. There is a lot of research going on now in an attempt to develop plant-based repellents which would be non-toxic. Catnip is showing a lot of promise. Although no one yet knows why it works, the nepetalactone which gives the plant its scent appears to be even more effective than DEET. Anecdotal evidence from individuals suggests possible repellent capabilities from cedar oil, rubbing alcohol, Vaporub, Avon Skin-So-Soft, vanilla, eucalyptus oil, and lavender, to name just a few. Since the purpose is mainly to cover up your own scent and not attract the mosquitoes, there are plenty of possibilities for experimentation. Rather than increasing our risk of exposure to West Nile Virus by attracting wildlife to our yards, enhancing our backyard habitat to attract mosquito predators and remove favorable conditions for mosquito reproduction is one of the best ways to reduce our risk of infection. Lowering the number of mosquitoes is obviously the best way to lower the chances of being bitten. This could include providing an environment which appeals to insect-eating birds by installing bluebird nesting boxes, landscaping with native plants which attract other insects (both as mosquito predators and as food for birds), and providing water sources. If you have a suitable location to attract purple martins, they will consume some mosquitoes, but unfortunately they aren’t very effective at reducing the population of that particular insect.

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Mosquitoes are most active in the early morning and late evening, in low vegetation, while purple martins feed during the day, high in the sky. Having purple martins on your property offers many other rewards, but don’t count on them to control mosquitoes. The situation is similar when it comes to bats. Depending on where you live, and the species that inhabit the area, bats may eat a significant number of mosquitoes, but their primary diet is moths and beetles. The little brown bat seems to be the most voracious consumer of mosquitoes, especially in urban areas, so it can be worthwhile to install bat houses and try to attract them. As with purple martins, bats provide many other benefits, so providing suitable habitat for them is definitely worthwhile for reasons other than the control of West Nile Virus. Mosquitoes can only reproduce when there is water available, but getting rid of birdbaths and ponds on your property is not a good step to take. All wildlife needs water, and it is becoming more and more limited, whether due to development, the filling in of wetlands, or drought conditions. As long as proper precautions are followed, providing water sources will encourage wildlife, including mosquito predators, without raising the risk of contracting West Nile Virus. While standing water can harbor mosquito larvae, the water that is preferred by birds and other wildlife is changed and freshened frequently, and, even better, may be kept in motion with a drip or small fountain system. Moving water does not attract mosquitoes. Standard bird baths should be filled with fresh water every one to two days.

Larger bodies of water such as ponds, even if they don’t include a waterfall or other source of movement, will encourage the presence of frogs and other creatures which happily eat mosquito eggs and larvae, as will any fish that you include. Female mosquitoes look for sheltered spots to lay their eggs, so don’t create “trapped" water, such as between rocks, in gravel, or in very shallow (less than 6") areas. Avoid plants with leaves that hang over the edges of the pond, since they will provide protection from predators. The tops of potted plants can provide suitable egg-laying areas if they extend out of the water, so keep them submerged. Pond sides should be steep, and provision should be made for future draining of the water if needed. If you incorporate a waterfall, avoid designing it with small pools that will hold calm water. Fish are wonderful mosquito predators, so allow sufficient depth in your pond to stock it. Remove excessive organic material, such as leaves or flowers, since it can decay and kill off the fish. Don’t overfeed your fish, and thin aquatic plants enough to allow the fish to swim easily throughout the pond. Be aware that frog eggs are also tasty fish food, so if you want to encourage amphibians to multiply you will need to have a section of your pond inaccessible to the fish. Visual inspection will allow you to detect mosquito larvae in the water. This will be easier if you collect a sample in a white container, which makes the larvae show up better. They will swim in a wiggling, sideways manner.

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Pupae are rounder and have a rolling motion. If you determine that you do have a mosquito presence, in addition to following all of the above practices, you might want to add a “mosquito dunk," which is a commonly-available donutshaped concentration of Bti (Bacillus thruingiensis israelensis). It will kill mosquito larvae (but not eggs or pupae) without harming birds or fish or other wildlife. These are also appropriate for birdbaths which don’t have moving water. If reading all of the above precautions still leaves you nervous, it is important to remember that humans are not very good hosts for West Nile Virus, and that only a small percentage of people will become ill even if they happen to get bitten by an infected mosquito. The toll is greater on wildlife, but it is thought that, as in countries where WNV has been common for many years, most species will develop a resistance to it through the process of natural selection. In the meantime, as we deal with its spread in this country, the answer to the problem isn’t to spray indiscriminately, or to use chemicals that can put us at potentially greater risk and harm wildlife and the environment. The best thing that we can do is replace or enhance wildlife habitat to keep it healthy, and encourage populations of mosquito predators. As you build ponds to attract dragonflies and frogs, plant native shrubs to feed birds, and curb your use of pesticides so that predatory insects can thrive, you will not only be helping wildlife, but you will be protecting yourself and your family.

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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

Information on mosquito prevention and control when building a pond: http://www.mosquitoes.org/Publicinfo/fpconst.html

West Nile Virus environmental issues: http://www.des.state.nh.us/factsheets/co/co-12.htm

Overview of history and the virus itself, geared towards teaching: http://www.riverdeep.net/current/2000/08/ 082500_westnile_arc.jhtml

Steps to take to minimize risk of being bitten/infected: http://www.ehs.cornell.edu/bio/WestNileVirus.htm

Extensive information on history, transmission, symptoms, repellents: http://www.continuingeducation.com/pharmacy/westnile/index.html

Good set of Frequently Asked Questions: http://www.metrokc.gov/health/westnile/

Answers to questions related to feeding birds: http://www.birdwatchers.com/WestNile.html

American Bird Conservancy view on West Nile and pesticide use: http://www.abcbirds.org/pesticides/west_nile_position_statement.htm

North American Butterfly Association on the effects of pesticides on other insects: http://www.naba.org/wnvirus.html://www.naba.org/wnvirus.html

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

Purple Martin facts, including why they aren’t good for mosquito control: http://www.purplemartin.org/update/ThirtWays.html

Discusses bat control of mosquitoes: http://www.texasmosquito.org/Bats.html

History of methods of mosquito control: http://www.ces.ncsu.edu/onslow/staff/drashash/newsletr/ Jul2001.html

Non-chemical mosquito control using Integrated Pest Management methods: http://www.colostate.edu/Depts/IPM/natparks/mosquito.html

Article on using catnip to repel mosquitoes: http://www.sciencedaily.com/releases/2001/08/010828075659.htm

Suggestions for homemade insect repellents: http://www.sciencedaily.com/releases/2001/08/010828075659.htm

EPA in-depth information on lavicides: http://www.epa.gov/pesticides/citizens/larvicides4mosquitos.htm

National Pesticide Information Center: http://npic.orst.edu/wnv/

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This article was written by Maryland Master Wildlife Habitat Naturalist Cathy Gilleland. For more information or for the name of a Master Wildlife Habitat Naturalist in your area, please contact: WindStar Wildlife Institute E-mail: wildlife@windstar.org http://www.windstar.org WindStar Wildlife Institute is a national, non-profit conservation organization whose mission is to help individuals and families establish or improve the wildlife habitat on their properties.

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