West Nile Virus and Wildlife


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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.

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West Nile Virus and Wildlife

  1. 1. 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 Plants Home With this in mind, you are encouraged to read this A Birds Home pamphlet, but also to visit the web sites which are A Homesteaders 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 Plants Home
  2. 2. 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.© WindStar Wildlife Institute Page 2 A Plants Home
  3. 3. 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.© WindStar Wildlife Institute Page 3 A Plants Home
  4. 4. 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.© WindStar Wildlife Institute Page 4 A Plants Home
  5. 5. 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.© WindStar Wildlife Institute Page 5 A Plants Home
  6. 6. 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/© WindStar Wildlife Institute Page 6 A Plants Home