New Threat
Mosquito-Borne Illness

by Mary K. Dagley

Date: Summer 1999
Location: East Coast
Situation: Campers, bitten by mosquitoes, develop malaria
How should camps respond? Here’s some background.

There are 150-200 species of mosquitoes in the United States. The majority of these species are little more than annoying pests that infringe upon outdoor leisure activities and work. However, some species of mosquitoes found in the U.S. are capable of transmitting serious diseases including malaria, dengue fever, and encephalitis. Given the nature of the camp experience, camp staff and campers may be particularly vulnerable to mosquito bites and thus mosquito-borne disease.

Camp directors have long been faced with the dilemma of mosquito control. Concern for the ecological impact of sprays, effectiveness of natural means of control, and concern for health risks posed by both the mosquito and the control agent make the decision complicated. Recent increases in mosquito-borne illness require directors to evaluate their risk-reduction procedures.

Mosquito-Borne Illnesses

Malaria is a parasitic disease transmitted from person to person through the bite of an infected mosquito. Symptoms of malaria include headache, back pain, chills, profuse sweating, myalgia, nausea, vomiting, diarrhea, and cough. Untreated, malaria can lead to coma, renal failure, pulmonary edema, and death. The disease was all but eradicated in the U.S. during the 1950s and suppressed in Third World countries during the 1960s. In recent years, however, malaria has reared its ugly head once again.

Incidences of malaria outbreaks have increased dramatically. This disease is responsible for an estimated 2.7 million deaths worldwide each year. Locally transmitted malaria has been found recently in California, Texas, Florida, Michigan, New Jersey, and New York City.

Dengue Fever is a severe hemorrhagic viral disease poorly understood by American physicians. It is primarily transmitted by mosquitoes present in southern Texas and the southeastern U.S. Clinical symptoms of dengue hemorrhagic fever are sudden onset of fever, severe headache, and muscle and joint pain. Dengue fever occasionally causes shock and hemorrhage, leading to death. Southern Texas and the southeastern U.S. have a small, but significant, risk for transmission and outbreaks because of dramatic increases in epidemic activity and geographic expansion in South America. Dengue is now endemic in eighteen South American countries. Imported dengue infections in Florida during 1997 and 1998 have been more frequent than expected.

Arboviral Encephalitides viruses are transmitted by a variety of mosquitoes found in the U.S. The main viral agents of encephalitis in the U.S. are identified below. Cases of encephalitis usually occur in the summer months (June – September) though cases can occur into the winter months in warmer areas of the country. The majority of human infections do not have any symptoms or may result in flu-like symptoms. Infection, however, can lead to full-blown encephalitis with fatal outcomes or permanent neurological consequences.

• LaCrosse Encephalitis (CAC) is most prevalent in children under sixteen years of age. The infection could result in mild illness (fever, headache, nausea, vomiting, lethargy) or progress to seizures and coma. The virus is transmitted through the bite of an infected tree hole mosquito. There are approximately seventy reported LAC encephalitis cases per year though it is believed that the illness is under-reported because the viral agent is often not identified. Reported cases generally occur in the upper Mid-Western states, Mid-Atlantic, and Southeastern regions of the U.S.

• Eastern Equine Encephalitis (EEE) is transmitted through several mosquito species. Symptoms of EEE include sudden onset of fever, general muscle pains, and headache. Many people will progress to severe symptoms including seizures and coma and approximately one-third of individuals infected will die from the disease or suffer permanent brain damage. Small human outbreaks have occurred in the Midwest, and along the Eastern Seaboard and Gulf Coast.

• Western Equine Encephalitis (WEE) is transmitted by several species of mosquitoes. Most infections have no symptoms or result in mild illness. More severe symptoms include sudden onset of fever, headache, nausea, vomiting, anorexia, and malaise. WEE is mainly seen in the western U.S. and Canada.

• St. Louis Encephalitis (SLE) is the most common mosquito-transmitted virus in the U.S. The virus is seen throughout the forty-eight states in the contiguous U.S. and is transmitted by mosquitoes found across the U.S. An average of 193 cases of SLE are seen each year; however, the majority of cases do not present symptoms and go undiagnosed. Symptoms range from mild (fever with headache) to severe (meningoencephalitis) with 95 percent of recognized cases requiring hospitalization for central nervous system infection. SLE cases are generally seen in the late summer or early fall, but can occur year-round in warmer climates. The most recent SLE outbreak occurred in New Orleans, Louisiana, in 1999.

• West Nile Encephalitis (WNE) is transmitted primarily by one species of mosquito. Fifty-nine cases, including seven deaths were identified in the New York City area in late August and September 1999. It is unknown how the virus arrived in the U.S. or how long it has been here. WNE can result in infections producing no symptoms or mild symptoms including fever, headaches, body aches, skin rash, and swollen lymph glands. In severe cases, the infection causes headache, high fever, stiff neck, disorientation, tremors, occasional convulsions, paralysis and, rarely, death.

Prevention

Prevention of mosquito-borne illness can be achieved in two major ways: personal protective measures and public health programs to reduce the mosquito populations.

Actions camps can take include eliminating mosquito breeding sites and providing barriers of protection against adult mosquitoes.

Eliminating Breeding Sites

The most effective way to control mosquito populations is to find and eliminate their breeding sites. The following are measures that should be taken to control mosquitoes:

• Destroy or dispose of tin cans, old tires, plastic sheeting, or other containers that collect or hold water. Stack containers upside down to prevent water collecting inside. Old tires are particularly well liked by mosquitoes for breeding areas.

• Clean debris from rain gutters and remove standing water under or around structures or on flat roofs. Check around faucets and air conditioning units, and repair leaks or puddles that remain for several days.

• Change the water in bird baths or wading pools at least once a week. Stock ornamental pools with top-feeding predacious minnows.

• Fill in or drain puddles, ditches, and swampy areas, and either remove, drain, or fill tree holes and stumps with mortar.

• Eliminate seepage from cisterns, cesspools, and septic tanks.

• Eliminate standing water around animal watering troughs.

• Carefully irrigate lawns and gardens to prevent water from standing for several days.

Controlling adult mosquitoes requires the camp to make a philosophical and practical decision on means of control. The camp should consult with local health or conservation authorities for recommendations of control agents, whether natural or chemical. Some effective adult mosquito-control options are:

• Keep mosquitoes outside by keeping doors, windows, and porches tightly screened with sixteen-to-eighteen inch mesh screens.

• Screen doors should open outward to prevent mosquitoes from following people in.

• Adult mosquitoes prefer to rest on weeds and other vegetation. Cut down weeds adjacent to building foundations and in yards. Mow lawns regularly to prevent weed growth.

• Apply insect repellants to the skin and clothing of campers and staff.

• Pressurized aerosol insecticide dispensers can be used inside to kill mosquitoes. Always be certain to follow label directions.

• Wear long-sleeved clothing and long pants to prevent bites at dusk and after dark when most mosquitoes are feeding.

• Use of mosquito netting may be indicated in high-risk areas or when sleeping outdoors. There are many resources on the Internet for purchasing mosquito netting.

Insect Repellents

Insect repellents are frequently used by individuals for personal protection against mosquitoes and other pests. Repellents frequently recommended for personal use in preventing mosquito bites are those containing active ingredients such as diethyl phthalate, diethyl carbate, diethyl toluamide (DEET) and ethyl hexanediol. DEET is used in many insect repellent products and does not kill mosquitoes, but acts to keep the insects from landing on a surface (such as skin or clothing) that is treated with a product containing this ingredient.

DEET has been implicated in seizures among children, but this effect has not been proven because of insufficient data. DEET is slightly toxic by eye, dermal, and oral routes. Overall environmental risk factors have not been identified, but DEET is slightly toxic to fish, birds, and aquatic invertebrates.

The Environmental Protection Agency (EPA) recently completed a reassessment of DEET and concluded that as long as consumers followed label directions and take proper precautions, products containing DEET do not present a health concern to the general population. It has been common practice to label certain products as safe for children because of a 15 percent or less formulation of DEET, however the EPA has found no evidence that any particular formulation is inherently safer for children. It is important to note that the EPA has deferred their decision on the use of DEET in sunscreens. Sunscreen application is recommended for frequent and generous use and may cause unnecessary increased exposure to the insecticide.

Oil of Citronella is a product that has been used extensively since 1948 and is not expected to pose health risks to people, including children or sensitive populations. Oil of Citronella can be found in liquid products that can be sprayed or applied to skin and clothing by hand. It is also commonly used in candles, torch oil, and rub-on products.

Choosing insect repellents should depend on the risk exposure. Mosquito repellents come in different forms (liquid, cream, lotion, spray) and concentrations of the active ingredient. For situations in which exposure to mosquitoes is minimal, a product containing a low concentration of the active ingredient should be chosen. Products with higher concentrations of the active ingredient should be used in mosquito-infested areas where exposure risk is higher. Always check the label for EPA approval and registration number. Do not use products containing active ingredients that have not been EPA approved.

Safe use recommendations:

• Apply repellents only to exposed skin or clothing, not under clothing.

• Read the product label and follow recommendations, even if you have used the product before.

• Avoid getting the product near the eyes or mouth and use sparingly around ears.

• When using sprays, do not spray directly on the face. Spray product on hands and then apply to face.

• Do not allow children to handle repellents. Do not apply to children’s hands.

• Spray in well ventilated areas and avoid breathing a repellent spray.

• Only use enough repellent to cover exposed skin and clothes. Avoid heavy applications.

• When returning indoors, wash treated skin with soap and water to remove the repellent. This is particularly important when using the product repeatedly. Also wash treated clothing before wearing again.

For specific information on the active ingredients in repellents and other pesticides, contact the National Pesticides Telecommunication Network (NPTN) at 800-858-7378. NPTN operates from 6:30 am to 4:30 pm (Pacific Time) or 9:30 am to 7:30 pm (Eastern Time) seven days a week.

Actions taken by public health authorities may involve permanent measures such as draining swampy areas where mosquitoes breed. Temporary measures of treating breeding areas to kill larvae and spraying to kill adult mosquitoes may also be undertaken by local public authorities.

Insecticides may used by state and local authorities in organized mosquito control management. The following is a list of EPA-approved insecticides most frequently used by state or local mosquito management authorities. (Note: state or local regulations may vary on the use of these insecticides.) It is important to note that insecticides are different than insect repellents. Insect repellents work to keep mosquitoes from landing on treated surfaces, however insecticides are engineered to kill mosquitoes.

• Malathion, when used for mosquito control, is required by the EPA to be applied at very low rates by sprayers operated by state or local applicators from trucks or aircraft. The EPA believes malathion can be applied in low concentrations with little risk to humans.

• Naled is mostly used for mosquito control in the southern states, particularly Florida and other Gulf states. Naled is primarily registered for use on land and should pose little risk to humans when applied at low concentrations; however, there is potential for acute and chronic risks for freshwater invertebrates.

• Sumithrin is an insecticide registered for mosquito control use in swamps, marshes, and recreational areas. Sumithrin can also be used in homes, gardens, greenhouses, and on pets. It is expected to pose little risk to humans when used in low concentrations for mosquito control.

• Resmethrin is only registered for outdoor use and is generally applied in very small amounts. This insecticide has low toxicity for humans, but is highly toxic to fish. Use of resmethrin products for mosquito control at or near aquatic sites are classified as "restrictive use pesticides" and can be used only by specially trained and licensed applicators.

• Bacillus spaericus and bacillus thuringiensis israelensis are biological pesticides used to control mosquito larvae in water. They are naturally occurring bacteria with low toxicity to humans.

Though the insecticides approved for use by the EPA are thought to have low toxicity to humans, there is still some toxic risk involved. Certain individuals may experience mild to severe allergic reactions to the active ingredients in the pesticide agents. Precautions to reduce exposure to these pesticides during spraying should be taken.

• Spray areas only when campers are not present or when they are indoors with windows and doors closed.

• If you are outdoors, avoid eye contact with the spray. If you get pesticides in your eyes, immediately rinse them with water or eye drops.

• Bring laundry and toys indoors before spraying begins and wash them with soap and water if exposed to pesticides during spraying.

• Bring pets indoors and cover ornamental fish ponds.

• Cover swimming pool surfaces if possible.

• Wash exposed skin with soap and water if you come into contact with pesticides.

• Wash exposed fruits or vegetables.

• If you think pesticides are making you sick, call the National Pesticides Telecommunications Network (NPTN) at 800-858-7378

Keep in mind that ACA standards require that chemicals be properly stored, used according to label instructions, and applied by persons trained in proper use.

Information contained in this article was obtained through the Center for Disease Control (CDC), the Environmental Protection Agency (EPA), and the American Mosquito Control Association (AMCA).

Originally published in the 2000 Winter issue of The CampLine.