West Nile Virus and Eastern Equine Encephalitis in Maine

Summer 2014

State develops plan for possible spraying

By MOFGA Staff

Arboviral diseases are transmitted by arthropod vectors such as mosquitoes and include Eastern Equine Encephalitis (EEE) and West Nile Virus (WNV). Because EEE and WNV have been detected in Maine, the Maine Legislature directed the Maine Department of Agriculture, Conservation and Forestry (MDACF) and the Maine Department of Health and Human Services (MDHHS) to develop a plan for protecting the public health from arboviral diseases.

That plan includes the possibility of ground and aerial spraying with an insecticide to control adult mosquitoes in certain areas in an emergency. The MDACF and MDHHS say that “in epidemic arboviral transmission settings, it has been consistently determined that the risk to human health from mosquito-borne diseases is greater than the risk of acute pesticide poisoning.”

Spraying – especially aerial spraying – is a risk for organic farms. One Vermont farmer lost use of a field in 2012 after it was contaminated by spraying to control WNV. In Maine, Board of Pesticides Control (BPC) rules limit options for a farm to be excluded from spraying, but towns can choose whether or not to exclude property from spraying.

Members of the public, including organic farmers, can help reduce the need for such spraying – and let towns know they have done so – by limiting mosquito breeding sites on their own land and encouraging their communities to do the same. They can also avoid being bitten by staying indoors, if possible, when mosquito populations are heavy and mosquitoes are biting (primarily between dusk and dawn) and, when outside, by wearing protective clothing and using repellents.

The Viruses
WNV exists in all 48 continental states. EEE is found primarily in the eastern United State (including Maine) and is rarer but more lethal when it occurs.
Occurrences – WNV      
Locations Dates No. Cases No. Deaths
U.S. 2012 5,674 human 286
2013 2,300 human 105
2012 1 human  
Occurrences – EEE      
U.S. 1964-2012 285 human
        71 – Florida
        45 – Mass.
        28 – Georgia
        20 – N.J.
U.S. 2012 15 human 5
              7 – Mass. 3
              2 – Vt. 2
U.S. 2013 6 human 3
Mass. 2008 1 human – virus possibly acquired in Maine  
Maine 2001-2012 Evidence in animals and mosquitoes in 15 of 16 Maine counties  
Maine 2009   15 horses and llamas
Maine 2013   3 horses, 1 flock of pheasants


Symptoms of EEE in humans usually begin four to 10 days after a bite from an infected mosquito. Many people infected with EEE virus have no symptoms; others may have mild flu-like symptoms with fever, chills, headache, general weakness, and body and muscle pain. If the central nervous system is infected, symptoms may include a sudden high fever (103 to 106 F), severe headache, stiff neck, chills and vomiting, which can be followed quickly by altered mental status, seizures, inflammation of the brain, coma and death. Those who survive may suffer permanent neurologic damage. No specific treatment for EEE exists.

In horses, symptoms of EEE can include fever, loss of appetite, drooping eyelids and lower lip, aimless wandering and circling, blindness and inability to stand. Young horses are most commonly affected. The infection kills horses in more than 90 percent of cases, usually within two to three days.

Symptoms of WNV in humans usually begin three to 15 days after a bite from an infected mosquito – although an estimated 80 percent of people infected with WNV show no signs of illness. Up to 20 percent have mild symptoms, such as fever, head and body aches, nausea, rash and swollen glands, which may last for days to months. Less than 1 percent develop serious illness with symptoms that can include high fever, altered mental status (e.g., disorientation), vision loss, neck stiffness, paralysis, convulsions, tremors, coma and sometimes death. People over age 50 are at higher risk of developing serious symptoms. A person who recovers from WNV is believed to be immune to future WNV infections, although immunity may decrease over time or with health conditions that compromise the immune system.

Controlling Larvae

Adult female mosquitoes lay eggs on the surface of standing water, including natural bodies of water (still ponds, wooded temporary pools, tree holes, salt marshes, bogs, swamps) and manmade containers (birdbaths, pools, roadside puddles …). Eggs develop into larvae, which undergo several instars before emerging as adults. Female adults bite humans, birds, horses and other animals, primarily between June and October.

Controlling mosquito larvae in a rural, wet state such as Maine “may be largely impractical” say state officials, as it would require enormous resources and would have to begin earlier in the year than the threat of mosquito-borne diseases could be characterized. Also, while eliminating stagnant water around homes is somewhat effective against WNV vectors, this strategy has limited effect on EEE vectors, which breed primarily in natural habitats that cannot be drained, such as maple and white cedar swamps. The EEE-carrying mosquitoes also breed in “crypts” among submerged tree roots and cattails in dispersed New England wetlands, where controls may not reach.

Still, taking steps like those below to control mosquitoes around your home, farm or community can reduce the insects’ populations somewhat, as some mosquito species travel less than 1,000 feet when winds are not strong. (Others can fly more than 40 miles.)

• Before mosquitoes emerge in late April, empty, clean or remove places where water may stagnate and allow mosquitoes to breed – old tires (drill holes in tires used to hold tarps down and in tire swings), open containers, rain gutters, birdbaths, cans and bottles, depressions in tarps and swimming pool covers and plastic mulch, roll-up sides of hoophouses, and areas near faucets and air conditioner units.

• Eliminate depressions in the landscape where water may puddle – including under animal watering troughs.

• Change water at least twice weekly in wading pools, birdbaths, pets’ dishes, flowerpot saucers, livestock watering troughs, urns and other open containers.

• Turn over plastic wading pools and wheelbarrows when not in use.

• Cover trash containers; screen water barrels.

• Aerate ornamental ponds with circulating pumps or stock them with native fish. Contact Maine’s Office of Inland Fisheries and Wildlife (207-287-5261) first to see whether permits are required for introducing specific fish to bodies of water.

• Clean and chlorinate swimming pools, outdoor saunas and hot tubs. Cover pools and hot tubs when not in use.

• Cut back or remove dense weeds, tall grass and bushes around houses and in wetlands and mow grassy areas to reduce sites where adult mosquitoes that transmit WNV can rest.

• Encourage native dragonflies, bats, birds, frogs, toads and other predators by maintaining habitat for them, including native plants around ponds, and by minimizing or eliminating pesticide use. Dragonflies do well around small ponds when adults can rest in the sun on vegetation growing from the water and on flat rocks around the pond. Dragonfly nymphs eat mosquito larvae, and adults eat mosquito adults.

• Communities can clear roadside ditches, culverts and storm water basins to avoid standing water.

Bacillus thuringiensis var. israelensis (Bti) or Bacillus sphericus (Bs), naturally occurring bacteria, can kill mosquito larvae when applied to bodies of water beginning in early spring and continuing throughout the season. They are believed to pose minimal risk to nontarget species. However, larval mosquito control programs in Maine are tightly regulated by the Maine Department of Environmental Protection (DEP), even for products such as Bti and Bs. Any discharge of pesticides to “waters of the state” is prohibited without a license. Be sure to contact the Maine DEP (207-287-7688) for needed permits; the Maine Board of Pesticides Control (207-287-2731) for information about pesticide applicator license requirements; and the University of Maine Cooperative Extension Pest Management Office (207-581-3880) for management recommendations. Bill Hinkel, an environmental specialist with the Maine DEP Division of Water Quality Management and a supervisor for industrial and municipal wastewater permitting, is especially knowledgeable and helpful; contact him at 485-2281.

Personal Protection

• Protect yourself from biting mosquitoes, especially from June to October.

• Wear long-sleeved shirts, long pants, mosquito netting and other protective clothing.

• Stay indoors when mosquitoes are most active –  especially from dusk to dawn.

• Be sure window and door screens fit well and don’t have holes.

• Place mosquito nets over strollers when mosquitoes are actively biting.

• Avoid wearing scented products; they may attract mosquitoes.

• Oil of lemon eucalyptus, a natural oil extracted from leaves and twigs of the lemon-scented gum eucalyptus plant, Eucalyptus citriodora, also called Corymbia citriodora, is registered by the EPA as a biopesticide repellent. It contains p-menthane-3,8-diol, or PMD. (“Pure” oil of lemon eucalyptus [e.g. essential oil] has not received similar testing for safety and efficacy and is not registered with EPA as an insect repellent.) According to Beyond Pesticides, “In tests against a 10% DEET repellent, PMD products, such as the Repel Brand (with 26% oil of lemon eucalyptus or 65% PMD), were shown to prevent bites for 4 to 7 hours after application for aggressive species of mosquito and for greater than 12 hours for less aggressive mosquitoes – a period of prevention greater than the studied DEET repellent.” A few drops of oil of lemon eucalyptus can be applied to the neck, face, hands and arms or to socks or other items of clothing. Keep the oil away from eyes and lips. Oil of lemon eucalyptus is not labeled for use on children under 3 years of age, and high concentrations may irritate skin. (PMD may also protect against deer ticks, which can carry Lyme and other diseases.)

• Bug zappers, sound emitters and scented geraniums do not appear to reduce mosquito populations.

• Vaccinate horses and other equids (e.g., donkeys, mules) annually. (No vaccine is available for humans.)

Protection from Spraying

If government-sponsored spray programs are initiated to control mosquito populations, you may have the option to “opt-out” of being sprayed. 

• In the event of a ground-based spray program, any landowner can opt-out of being sprayed, but you must take the initiative to opt out.

• In the event of aerial applications, the entity in charge of the spray program may choose to allow certified organic farms to be excluded. Certified organic farmers must make the case to their municipality that their farm should be excluded in the event of an emergency. 

How these processes will occur in the event of a public health emergency is still unclear. However, once an emergency occurs, all the planning and provisions for exclusion from spraying will likely occur within days. If you are concerned about the potential for spraying in your community, you can stay informed about monitoring results via the Maine CDC website: https://www.maine.gov/dhhs/mecdc/infectious-disease/epi/vector-borne/arboviral-surveillance.shtml.


American Mosquito Control Association

Eastern Equine Encephalitis, University of Minnesota, Center for Animal Health and Food Safety

Eastern Equine Encephalitis in Vermont 2013, Vermont Department of Health

Mosquito Management Fact Sheet, by James F. Dill and Griffin M. Dill, 2010, UMCE Pest Management

Oil of Lemon Eucalyptus – Beyond Pesticides Fact Sheet, Pesticides and You, Fall 2010;

Report To the Joint Standing Committee on Agriculture, Conservation and Forestry Pursuant to Resolve 2013, Chapter 13 Concerning the Development of A State Plan to Protect the Public Health from Mosquito-borne Diseases, Submitted by the Maine Department of Agriculture, Conservation and Forestry In Cooperation with the Maine Department of Health and Human Services, December 20, 2013 (source for data in table above).

Updated information on arborviral activity in Maine

Vector-borne Diseases, Maine Center for Disease Control & Prevention, Division of Infectious Diseases (links to fact sheets on WNV and EEE)

West Nile Basics, California West Nile Virus Website

West Nile Virus, Centers for Disease Control and Prevention

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