United States Environmental Protection Agency

Protect Yourself West Nile Virus (WNV) first appeared in the United States in 1999. Since its inital outbreak in New York City, the virus Wear long sleeves and has spread across the country from East to West. Female pants, especially when near stagnant or mosquitoes transmit the virus primarily by infecting polluted water. birds. Occasionally, mosquitoes transfer the virus from birds to humans, most of whom experience no Be mindful of symptoms. One out of five infected people develop West mosquito activity, Nile fever, characterized by mild, flu-like symptoms. which peaks at dusk Infection can sometimes, although rarely, be fatal for and dawn in summer months. humans. Since West Nile is lethal in some bird species, unusual bird deaths may signal human outbreaks. Consider using mosquito repellants, if Are Wetlands a Threat? swamps and salt marshes altogether. necessary, that contain DEET. ealthy wetlands are not uncontrolled Damaged or degraded wetlands can provide ideal H breeding grounds for mosquitoes. habitat for some mosquito species that carry West Healthy wetlands sustain numerous species of Nile. Excess nutrients in contaminated waters can mosquito-eating fish, amphibians, insects and spur microbial growth and cause harmful algal birds, all of which help limit mosquito blooms, which feed mosquito larvae. Filling or populations. draining wetlands may also increase mosquito outbreaks, as an altered landscape with stagnant The principal mosquito carrier of West Nile pools of water may no longer contain mosquito virus on the East coast, Culex pipiens, does predators. not prefer to reproduce in most wetlands. These species reach greatest numbers in large Sometimes, even healthy wetlands may harbor urban centers, breeding easily in artificial large numbers of mosquito species that carry containers—birdbaths, discarded tires, WNV. Unlike Culex pipiens, Culex tarsalis, the buckets—and in human-created environments, major WNV vector in western states, prefers to such as clogged gutters, animal waste lagoons breed in clean water. Therefore, it may be Broadleaf arrowhead and sewage effluent. Adapted to polluted necessary to use appropriate mosquito control habitats, these Culex species generally avoid measures to prevent WNV disease transmission. Disease Transmission Culex pipiens (House mosquito) Mosquitoes are the primary vectors of West Nile, meaning they carry Culex pipiens is the primary West Nile vector in the the virus from host to host. While nectar is their primary food source, eastern United States. It can be found in urban and females take blood in order to develop their eggs. Mosquito activity is suburban settings, has a flight range of 1/4 to 1 mile and reduced in colder months, but the virus may still persist in dormant prefers to breed in standing water, especially in water mosquitoes and eggs that survive winter. polluted with organic matter. The Centers for Disease Control and Prevention (CDC) reports that 43 Culex salinarius Found in fresh and saltwater marshes, lakes and ponds, mosquito species in the United States have tested positive for West Nile Culex salinarius also prefers artificial containers around virus. The most common carriers are the HouseCulex mosquito pipiens (Culex human residences and businesses. Because it readily pipiens) on the East coast and Culex tarsalis inFlight the W range:est. Because ¼ mile it - 1 mile feeds on humans, evidence indicates that it may be readily feeds on humans, Culex salinarius is alsoFeeding an important times: duskvector. to dawn responsible for transmitting West Nile to people. Habitat: stagnant pools, artificial Since mosquitoes primarily infect birds, unusualcontainers bird deaths may signal Culex tarsalis (Western Encephalitis mosquito) a WNV outbreak and should be reported to appropriateSeasons: late local, Spring county to or Fall An abundant mosquito in Western States, it breeds state agencies. Based on analysis of 2001 and 2002 data, the CDC primarily in irrigated agricultural areas and in temporary or seasonal depressions. It is most active at dusk and reports that counties that report WNV-infected dead birds early in the feeds on humans, domesticated animal and birds. It is the transmission season are more likely to report subequent WNV disease primary vector for West Nile in the midwestern and cases in humans. western states. Protect Your Home & Community Wetland Restoration Eliminate stagnant water and Mosquito Reduction in New Hampshire Limit the number of places available for Prior to its restoration in 1999, the two-acre Edmond Avenue wetland mosquitoes to lay their eggs by was in critical condition. Residential development near Portsmouth, 1eliminating standing water sources from New Hampshire, had partially filled the wetland, and urban and around your home (e.g., tires, garden pots stormwater runoff had contaminated the water. Increased sedimentation and bird baths). had reduced the extent of open water, and invasive plants choked out Protect wetlands from pollution native species. Including runoff from farms, lawns and roads with buffers, since By 1996, the continued degradation 2contaminated water attracts of the Edmond Avenue wetland mosquitoes. transformed the ecosystem into a major breeding site for mosquitoes, Check Stormwater Systems including the Culex species primarily Ensure that stormwater Degraded wetland - shallow, responsible for West Nile stagnant pools harbor many transmission. During 1996-1999, the catchments and constructed mosquitoes. 3wetlands are properly designed application of mosquito larvicides and maintained. and sprays jumped to 4-5 times per year, a four-fold increase from the previous 15 years. Since its restoration in 1999, the Edmond Avenue Install Screens wetland no longer requires mosquito Install or repair screens on doors control measures. The restored and windows so that mosquitoes wetland lacks stagnant depressions 4cannot get indoors. and is deep enough in some areas to support fish that eat mosquitoes. Wave action also disrupts mosquito Consider Using Pesticides breeding. Results have been If necessary, try larvicides before astonishing—a near 100% reduction adulticides, since larvicides more 5 in mosquito habitat and the virtual Restored wetland - carefully effectively control mosquitoes. elimination of Culex species, not to designed open water habitat Carefully follow instructions on the mention improved water quality and supports ducks, as well as fish that pesticide’s label. bird habitat. eat mosquitoes. EPA 843-F-04-010 Frequently Asked Office of Water August 2004 Questions: • How many people have become infected with WNV? Centers for Disease Control and Prevention, West Nile Virus For 2003, the CDC recorded 9,858 human cases http://www.cdc.gov/ncidod/dvbid/westnile/ and attributed 262 deaths to WNV nationwide. • Will draining or filling a wetland prevent Maps of West Nile Occurence in the United States WNV? http://westnilemaps.usgs.gov Draining or filling wetlands is not a necessary or appropriate way for controlling mosquitoes or State and Regional Information WNV. Healthy, functioning wetlands typically http://westnilevirus.nbii.gov/states/ have a balanced predator-prey relationship that provides natural mosquito control measures. Draining or filling a wetland may require a Cornell University, Center for the Environment federal, state, tribal or local permit. Contact http://environmentalrisk.cornell.edu/WNV your regional Army Corps of Engineer’s Office. • How far do mosquitoes travel? American Mosquito Control Association htttp://www.mosquito.org Many of the mosquitoes that transmit WNV have very short flight ranges. Therefore, eliminating backyard mosquito habitat, such as EPA’s Wetlands Division stagnant water or blocked roof gutters, can help http://www.epa.gov/owow/wetlands control mosquito populations.