West Nile Virus and Wildlife

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This pamphlet summarizes the latest information on thevirus at the time of writing. As with any medical subject,however, information changes frequently, based on theresults of new research or changes in the virus itself.

With this in mind, you are encouraged to read thispamphlet, 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.

Usually when we complain about"problem wildlife," we’re talkingabout annoyances: deer nibblingour shrubs; squirrels devouring ourtulip bulbs; raccoons raiding ourtrash cans.

Generally we try advice fromfriends and authorities, and eithersolve the problem or come to somekind of tolerance andaccommodation.

Sometimes, however, much moreserious concerns also tie into ourlove of wild creatures. In recentyears, one of the most frighteningof these has been the spread ofWest Nile Virus (WNV).

Learning that it is present inwild bird populations, and nowappears to be spreading tomammals, can make us wonder ifour fondness for wildlife and ourattempts to enhance wildlifehabitat are actually putting ourown health and that of ourfamilies at risk.

Somewhat surprisingly, we don’tknow the exact origin of thespecific virus that has reachedthe United States, although WNV

is fairly common in Africa, WestAsia, and the Middle East. Thefirst outbreak in this country inNew York City in 1999 seems to berelated to a strain that appearedin Israel the previous year.

At this point, experts considerit to now be permanentlyestablished in the WesternHemisphere and, depending onthe local climate, it can beoverwintered or transmitted allyear around.

As Paul Epstein of HarvardMedical School’s Center for Healthand the Global Environmentexplained in Scientific American,global warming has contributed toconditions that favor diseases likeWNV. Mild winters allow its survivalinto the spring, giving it an earlierstart in the year, while droughtkills insect predators such asladybugs and lacewings.

Drought also causes birds andmosquitoes to congregate inlarger numbers at smaller andfewer water sources, increasingthe likelihood of spreading thevirus, while higher temperaturescause an increase in mosquito

West Nile Virusand Wildlife

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activity, which means fasterreproduction and maturation ofthe virus, and a greater number ofpotential bites.

Of all the types of mosquitoes,the one in the United States whichis the most common carrier ofWNV is Culex pipiens. It is mostprevalent in urban environments,rather than in healthy wetlandsand wild areas. It is the femalemosquito that does the biting,needing the protein in blood toensure proper development of hereggs.

When the insect bites aninfected animal, the virus is storedin the mosquito’s salivary glands,and then can be transmitted tothe next "host" that is bitten.

Mosquito eggs are laid inbunches, and each bunch cancontain hundreds of eggs, so it’seasy to see why they can multiplyquickly. In addition, the eggs canbe dormant for years if there is adrought, then hatch when waterreturns.

It is important to remember,however, that even in places wherethe disease has been confirmed,it is actually carried by a very lowpercentage of the mosquitoes inthat area.

At one time crows seemed to beboth the primary sources andvictims of WNV. Now, however, morethan 140 species of birds havebeen reported, as well many othercreatures including horses, cats,dogs, chipmunks, skunks, bats,squirrels, bears, alligators, anddomestic rabbits.

At this time, many areas stillrequest that dead birds bereported to the local healthdepartment. However, these birdsmight not be physically collectedby authorities in that jurisdictionif the presence of WNV has alreadybeen established, since furthertesting would not yield anyadditional useful information.

Most birds and animals whichare infected will survive. That beingsaid, the virus is expanding withinmany wildlife populations, and canbe expected to affect greaternumbers in the future.

It is also spreading surprisinglyquickly throughout the country,found now in nearly every state,just over three years after itsfirst appearance in NY.

The fact that WNV is not host-specific is of great concern. Evenexotic wildlife in zoos is beingaffected, putting breedingprograms in jeopardy.

In natural areas where certainspecies are hit hard by the virus,the balance of nature can shift.For example, rodents canproliferate if the number ofraptors drops.

As native wildlife is stressedmore and more by other factors,such as habitat destruction,drought, and pesticide use, it ismore important than ever that wereplace lost habitat and becomeeducated on what can be done toattract and help wildlife withoutendangering ourselves or ourfamilies..

There are no documented casesof a person getting WNV fromanother person or from ananimal. This is an importantdistinction for those who care foranimals, whether wild ordomestic.

Although there is evidence thatbirds can now pass the virusdirectly to other birds, mostanimals don’t seem to transmitthe virus to other animals, sohaving an infected pet in contactwith other pets, or encouraginggroups of wildlife to congregate,doesn’t directly encourage thespread of the disease.

The main danger is that amosquito will bite the infectedanimal and then spread WNV by

biting another animal in the samevicinity. For this reason certainhabitat elements, such as birdfeeders, should be more numerousand placed farther apart than youmight normally have planned.

At this time, indications arethat the originally-infected animalis only infectious (throughmosquito transmission) for a fewdays. Birds are considered“reservoir" hosts, since an infectedbird can transfer the virus tomany mosquitoes.

Interestingly, humans and someother mammals, such as deer, arecalled “dead end" hosts. Thismeans that the virus doesn’t stayviable in their bodies long enoughfor them to transfer it to a lot ofother mosquitoes.

For some reason, while somedead end hosts (such as humansand horses) can get sick, others(like dogs and cats) can beinfected but won’t become ill.

An infected animal or bird canserve as a valuable warningsystem to people, indicating thatthere are infected mosquitoes inthe area, and that precautionsshould be taken to avoid gettingbitten.

While there is no evidence that aperson can be infected by handlingwildlife, whether it is alive or dead,that has WNV, it is a reasonableprecaution to wear gloves whendoing so, and to avoid getting anyblood from a suspected infectedanimal on an open wound.

There is also no evidence that aperson can contract the virus byeating an infected bird or animal,but it is prudent to be sure thatthe meat is well-cooked beforebeing consumed.

It is very important toemphasize the low risk to humans.Most people who are infected withWNV will not actually have anysymptoms.



In those few cases where thedisease is present, symptomsappear 3 to 14 days after beingbitten. Only about 20 percent ofthose affected will have the typicalfever, headache, flu-like bodyaches, and perhaps a rash andswollen lymph glands. These mildforms of the virus usually last justa few days.

There is some evidence that thevirus can be transmitted throughbreast milk, but there are noreports of any infants infected inthis way showing serioussymptoms, and the benefits ofbreast-feeding are felt to outweighany possible risks.

Overall, children less than one-year-old are rarely infected by thevirus. There is no evidence thatWNV can be transmitted throughpregnancy or birth.

Of those adults who do havesymptoms, less than one percentwill become seriously ill. Those over50 years of age, or withcompromised immune systemsfrom other causes, are the mostat risk for more serious cases ofthe disease. These more severesymptoms (including high fever,stiff neck, disorientation, andtremors) can last several weeks.

At this time it is assumed thatanyone infected with WNV willacquire lifelong immunity.

There have been some reportsabout possible transmission ofWNV through blood transfusionsor organ transplants. This is beingstudied carefully, and physiciansand blood banks are now aware ofthe issue and are being as carefulas possible.

It is important to rememberthat donating blood poses no riskto the donor, and that it is criticalthat the nation’s blood supply bekept at safe levels. Severalcompanies are working to developscreening tests, vaccinations, andtreatments, but nothing is yet

available at the time of thiswriting.

Often the first reaction ofcommunities faced with evidenceof WNV is to call for chemicalspraying of neighborhoods andwetlands. This process canchange the natural environment,actually making it morehospitable to mosquitoes bykilling predators (such as fish,other insects, and birds).

In addition, most insecticideshave been designed for agriculturaluse, and have not been tested orevaluated for repeated contactwith humans.

A further concern is the speedat which insects reproduce, givingthem the ability to build up aresistance to an insecticide farmore rapidly than largerpredators. Some of these, such asbats, may actually die out in anarea before they can build up atolerance, while the newly-adaptedmosquitoes will keep onmultiplying.

There are two kinds of pesticidesused: adulticides, which target themature mosquitoes, and larvicides,which are aimed at the eggs andlarvae. Adulticides are the lessefficient and potentially the moredangerous of the two.

Some communities spray withmalathion, an organophosphate.Organophosphates are known tobe nerve toxins, and as such needto be used with extreme cautionsince the results of long-termhuman exposure are not yet known.

Other commonly-usedadulticides are based onpyrethroids, which are derived fromthe flowers of the pyrethrumplants (such aschrysanthemums) or a syntheticequivalent.

Pyrethroids break down quickly,especially in sunlight, and theybind to the soil so they are less of

a threat to the environment.However, they are highly toxic tobees and aquatic life, so anybenefits are not without seriousdrawbacks.

Any adulticide product will killall insects indiscriminately. Notonly does this lower thepopulation of beneficial insects,but it also cuts down on thefood supply for both local andmigratory insect-eating birdspecies.

Larvicides tend to be moreeffective in controlling mosquitopopulations than adulticides.They can be applied selectively, inmore controlled conditions. Theyinclude both natural bacteria andchemicals. Some of the morecommon ones are microbial Bti,which kills the larvae when theyingest it, and surface oils whichare spread on top of water tosuffocate eggs, larvae, andpupae.

Although safer thanadulticides, larvicides can behighly toxic to aquatic life,including amphibians, insects,and fish, and in high doses cancause serious reactions inhumans.

Reducing the number ofmosquitoes is obviously the bestway to lower the chances of beingbitten, but there are manyprecautions that people can takewhich pose no danger to wildlifeor the environment. Basic homemaintenance is important,including making sure that thereare screens on windows anddoors, and that these screensare free from holes that wouldallow the insects to enter.

In the yard, watch for anycontainers that could retainstanding water, even in very smallamounts. These might include old

tires, flower pots, cloggedgutters, pool covers, evenchildren’s toys.



Eliminate these, or empty themfrequently, at least every coupleof days. Drill holes in the bottomof larger containers, such asthose used for recycling, if theyare kept outside. Turn overwheelbarrows and buckets.

You should wear light-coloredlong-sleeved shirts and longpants when outdoors during theday. Dark clothing attracts theinsects because it looks like acool, shadowy area. Put mosquitonetting over baby-carriers, andavoid being out at dawn and dusk,when mosquitoes bite the mostfrequently.

Not all species of mosquitoesare attracted to light, so lighttraps are not effective, andusually end up killing many morebeneficial insects than harmfulones.

In one study, of the 10,000bugs killed by a “bug zapper," onlyeight were mosquitoes. Othertests produced similar results,killing far more beneficial insectsand mosquito predators thanmosquitoes themselves.

Many people turn to insectrepellents for protection.Mosquitoes find their victims bysmell, either from the scent ofthe skin, or the odor of exhaledcarbon dioxide. Insect repellentsdon’t kill mosquitoes, they justcover the odors which wouldnormally attract them, renderingus somewhat “invisible."

The most effective repellent onthe market seems to be DEET (N,N-diethyl-m-toluamide). Higherpercentages of DEET within arepellent means that theprotection will last longer, but itwon’t be any more directlyeffective in repelling the insects,and a concentration of more than50 percent doesn’t continue toincrease the length of protectiontime.

Concentrations vary fromproduct to product. According tothe Centers for Disease Control, aproduct containing 23.8 percentDEET provides five hours ofprotection, while 6.65 percentprotects for two hours.

If you are concerned about anynegative effects from DEET, youcan apply concentrationsappropriate for the amount oftime that you expect to beoutdoors, then reapply ifnecessary.

There have been numerousstudies on the safety of DEET,and it appears to cause only rarenegative reactions in sensitivepeople. All the same, youshouldn’t use a higherconcentration than you need, andit’s important to apply it asdirected.

Don’t put the repellent on openor irritated skin, or on skin thatwill be covered with clothing. Youshould spray the clothing itself,and then wash it before wearing itagain.

You don’t need to apply DEET inlarge amounts in order to get fullprotection, and you should washany treated skin once you comeback indoors.

If using spray repellent, avoidgetting it in your eyes or mouth byspraying it on your hands and thenrubbing it on your face and neck.

Although no serious illnesseshave been reported in children,cautious experts advise usinglower concentrations (10 percentor less) of DEET on those from 2to 12 years old, while others evenapprove it for infants over twomonths old.

It is better for adults to putrepellent on their own hands, andthen apply it to children. Avoidputting it on the hands of youngchildren, since their hands usuallyend up in their mouths. There have

been no reported cases ofnegative reactions to DEET inpregnant or nursing mothers.

There is a lot of research goingon now in an attempt to developplant-based repellents whichwould be non-toxic.

Catnip is showing a lot ofpromise. Although no one yetknows why it works, thenepetalactone which gives theplant its scent appears to be evenmore effective than DEET.

Anecdotal evidence fromindividuals suggests possiblerepellent capabilities from cedaroil, rubbing alcohol, Vaporub, AvonSkin-So-Soft, vanilla, eucalyptusoil, and lavender, to name just afew. Since the purpose is mainly tocover up your own scent and notattract the mosquitoes, there areplenty of possibilities forexperimentation.

Rather than increasing our riskof exposure to West Nile Virus byattracting wildlife to our yards,enhancing our backyard habitatto attract mosquito predatorsand remove favorable conditionsfor mosquito reproduction is oneof the best ways to reduce ourrisk of infection.

Lowering the number ofmosquitoes is obviously the bestway to lower the chances of beingbitten.

This could include providing anenvironment which appeals toinsect-eating birds by installingbluebird nesting boxes, landscapingwith native plants which attractother insects (both as mosquitopredators and as food for birds),and providing water sources.

If you have a suitable location toattract purple martins, they willconsume some mosquitoes, butunfortunately they aren’t veryeffective at reducing thepopulation of that particularinsect.



Mosquitoes are most active inthe early morning and lateevening, in low vegetation, whilepurple martins feed during theday, high in the sky. Having purplemartins on your property offersmany other rewards, but don’tcount on them to controlmosquitoes.

The situation is similar when itcomes to bats. Depending onwhere you live, and the speciesthat inhabit the area, bats mayeat a significant number ofmosquitoes, but their primary dietis moths and beetles.

The little brown bat seems tobe the most voracious consumerof mosquitoes, especially inurban areas, so it can beworthwhile to install bat housesand try to attract them. As withpurple martins, bats providemany other benefits, soproviding suitable habitat forthem is definitely worthwhile forreasons other than the controlof West Nile Virus.

Mosquitoes can only reproducewhen there is water available, butgetting rid of birdbaths and pondson your property is not a goodstep to take. All wildlife needswater, and it is becoming moreand more limited, whether due todevelopment, the filling in ofwetlands, or drought conditions.

As long as proper precautionsare followed, providing watersources will encourage wildlife,including mosquito predators,without raising the risk ofcontracting West Nile Virus.

While standing water can harbormosquito larvae, the water that ispreferred by birds and otherwildlife is changed and freshenedfrequently, and, even better, maybe kept in motion with a drip orsmall fountain system. Movingwater does not attractmosquitoes. Standard bird bathsshould be filled with fresh waterevery one to two days.

Larger bodies of water such asponds, even if they don’t include awaterfall or other source ofmovement, will encourage thepresence of frogs and othercreatures which happily eatmosquito eggs and larvae, as willany fish that you include.

Female mosquitoes look forsheltered 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 thathang over the edges of the pond,since they will provide protectionfrom predators. The tops ofpotted plants can providesuitable egg-laying areas if theyextend out of the water, so keepthem submerged.

Pond sides should be steep,and provision should be made forfuture draining of the water ifneeded. If you incorporate awaterfall, avoid designing it withsmall pools that will hold calmwater.

Fish are wonderful mosquitopredators, so allow sufficientdepth in your pond to stock it.Remove excessive organicmaterial, such as leaves orflowers, since it can decay and killoff the fish.

Don’t overfeed your fish, andthin aquatic plants enough toallow the fish to swim easilythroughout the pond. Be awarethat frog eggs are also tastyfish food, so if you want toencourage amphibians to multiplyyou will need to have a section ofyour pond inaccessible to thefish.

Visual inspection will allow youto detect mosquito larvae in thewater. This will be easier if youcollect a sample in a whitecontainer, which makes the larvaeshow up better. They will swim ina wiggling, sideways manner.

Pupae are rounder and have arolling motion.

If you determine that you dohave a mosquito presence, inaddition to following all of theabove practices, you might wantto add a “mosquito dunk," whichis a commonly-available donut-shaped concentration of Bti(Bacillus thruingiensisisraelensis). It will kill mosquitolarvae (but not eggs or pupae)without harming birds or fish orother wildlife. These are alsoappropriate for birdbaths whichdon’t have moving water.

If reading all of the aboveprecautions still leaves younervous, it is important toremember that humans are notvery good hosts for West NileVirus, and that only a smallpercentage of people willbecome ill even if they happento get bitten by an infectedmosquito.

The toll is greater on wildlife,but it is thought that, as incountries where WNV has beencommon for many years, mostspecies will develop a resistanceto it through the process ofnatural selection.

In the meantime, as we dealwith its spread in this country,the answer to the problem isn’tto spray indiscriminately, or touse chemicals that can put usat potentially greater risk andharm wildlife and theenvironment.

The best thing that we cando is replace or enhance wildlifehabitat to keep it healthy, andencourage populations ofmosquito predators.

As you build ponds to attractdragonflies and frogs, plantnative shrubs to feed birds, andcurb your use of pesticides sothat predatory insects canthrive, you will not only be helpingwildlife, but you will be protectingyourself and your family.



RESOURCES

For further reading and the latest information, call your local healthdepartment 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 onother 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 theEnvironmental Research Foundation about pesticide use:http://www.rachel.org/home_eng.htm

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

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

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

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

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

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

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

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

This article was written byMaryland Master WildlifeHabitat Naturalist Cathy

Gilleland.

For more information or for thename of a Master Wildlife

Habitat Naturalist in your area,please contact:

WindStar Wildlife Institute

E-mail: [email protected]://www.windstar.org

WindStar Wildlife Institute is anational, non-profit

conservation organizationwhose mission is to helpindividuals and families

establish or improve the wildlifehabitat on their properties.


Self Improvement

West Nile Virus and Wildlife