West Nile Virus

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OUTDOOR ACTIVITIES DURING MOSQUITO SEASON

Q. When is mosquito season in Southeastern Michigan?
A. Mosquitoes are generally active from April until the first hard freeze in the Fall [usually mid- to late October].

Q. Is there a specific time of day when mosquitoes are most active?
A. Mosquitoes tend to be most active from dusk until dawn. However, it should not be forgotten that mosquitoes may also be very active during the day time in areas which are heavily overgrown with vegetation.

Q. What are the concerns associated with mosquitoes?
A. For the most part mosquitoes are a nuisance, and can drastically reduce our enjoyment of the out of doors. Very rarely they can be associated with a number of diseases, including such "exotic" illnesses as malaria, yellow fever, and dengue fever.

However, although human cases are rare, the concern in Southeastern Michigan is with several viral infections that can attack the central nervous system, such as: Eastern Equine Encephalitis, Saint Louis Encephalitis and more recently West Nile Virus.

Q. How are these diseases spread?
A. All of these illnesses are spread to humans by the bite of an infected mosquito. You cannot get them from a person who has the disease, nor are they spread by person-to-person contact such as touching, kissing, or caring for someone who is infected.

Q. What are the symptoms of Encephalitis?
A. Most people infected will either have no symptoms or experience a mild illness with symptoms such as a fever, headache and body aches before a full recovery. However, some individuals may develop more serious symptoms that affect brain tissue. These symptoms include the rapid onset of severe headache, high fever, stiff neck, confusion, muscle weakness, and coma. Death may occur in some instances.

Q. Are children or infants at a greater risk for becoming infected with these diseases?
A. Anyone can become infected with a mosquito- borne illness if bitten by an infected mosquito. However, there is no evidence that children, including infants, are at any greater risk of infection than other individuals. But remember that children need an adult's help in taking necessary precautions to prevent mosquito bites.

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Q. Who is at greatest risk from illness associated with encephalitis?
A. While it does not appear that anyone who lives in an area where mosquito-borne virus activity has been identified is at any greater risk of being bitten by an infected mosquito. Persons greater than 50 years old have a higher risk of serious illness if they are infected.

Q. If someone in my family is bitten by a mosquito, should he or she be tested?
A. No, even in those areas where mosquito-borne illnesses are present very few mosquitoes are infected.

Q. If someone in my family is bitten by an infected mosquito, will he or she get sick?
A. Most people, including children, who are bitten by infected mosquitoes, will experience either no symptoms at all or at the worst a very mild illnesses.

Q. Should we seek medical attention if we think that someone in my family has become infected with one of the encephalitis type illnesses?
A. Even though the chances that someone would become infected are slight, you should contact a doctor immediately if anyone in your family develops symptoms such as high fever with confusion; muscle weakness; severe headaches; stiff neck; or if his or her eyes become sensitive to light.

Q. What steps can I take to control mosquitoes?
A. Eliminate any source of standing water around your home. Fill in low areas where rain water may accumulate and dispose of discarded tires or other objects that can hold water.

Maintain property by mowing lawns on a regular basis and cutting down weeds that may act as resting areas for mosquitoes.

Keep your doors and windows tightly screened to prevent mosquitoes from entering your home.

Remember that spraying insecticides to kill adult mosquitoes is only a temporary solution.

For further information see the pamphlet "Controlling Mosquitoes around the Home."

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Q. Should I stay indoors and limit outdoor activities?
A. It is not necessary to limit outdoor activities but precautions should be taken during time periods when mosquitoes are most active.

Q. What personal precautions should I take when I'm outdoors at these times?
A. From April to the Fall, when mosquitoes are most active, take the following precautions:

If outside in an area that has a heavy mosquito population or during those times when mosquitoes are most active, children and adults should wear protective clothing such as long pants, long-sleeved shirts, and socks.

Consider using an effective insect repellent.

If using a repellent that contains DEET [N, N-diethyl-methyl-meta-toluamide], remember that it should be used only ACCORDING TO MANUFACTURER'S DIRECTIONS.

Note that Vitamin B, ultrasonic devices, incense and bug zappers have not been shown to be effective in preventing mosquito bites.

Q. When working outdoors do I need to change my safety practices?
A. Unless you are working during those time periods when mosquitoes are most active, it should not be necessary for you to change your usual outdoor work schedule or practices unless there is evidence of mosquito-borne disease in the area. If it is necessary to work during those periods the precautions listed above will reduce your risk of infection.

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CONTROLLING MOSQUITOES AROUND THE HOME

The following information provides the home-owner with a number of steps they need to take in order to effectively control mosquitoes on their property.
However, it is important to remember that mosquitoes are a community wide problem, requiring each of us to do our part. Please share this information with your neighbors and help those who may be physically unable to perform some of these tasks.

Mosquito Facts

• All mosquitoes require two items in order to lay eggs: A blood meal to allow the eggs to develop and water in which to lay their eggs.
• Mosquitoes do not breed in tall grass as many people believe. However, tall grass and other shady protected areas such as shrubs and ornamental trees with low lying branches provide mosquitoes with much needed shelter and resting areas.
• A mosquito can grow from an egg to an adult in less than 10 days when the weather is favorable.
• Mosquitoes are expert fliers and many species can travel great distances from their breeding sites. However, the species that breed around the home are often called "domestic" and are rarely found far from human habitation.
• All of the domestic forms will accept humans as a blood meal host and many will enter houses to feed.
• The most common mosquitoes found in urban and suburban areas will lay their eggs in virtually any receptacle containing water and decomposing organic material such as leaves, grass clippings or even algae.
• Breeding habitats around the home may include: discarded tires, unwashed bird baths, clogged rain gutters, plastic wading pools, toys left outside or virtually any other water source allowed to lie stagnant for at least four days.

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Reducing Mosquitoes Around the Home

• Provide screening [16-18 mesh] on all outside openings [doors, windows, etc.].
• Wear an effective insect repellent, long sleeve shirts and long pants when going into an area with a high mosquito population.
• Mosquitoes can be significantly reduced by eliminating as many sources of standing water as possible.
• Dispose of tin cans, plastic containers, ceramic pots or similar water-holding containers that have accumulated on your property.
• Dispose of discarded tires which are an important breeding site for domestic mosquito.
• If your child has a used tire as a swing, drill holes in the bottom to allow rain water to drain out.
• Drill holes in the bottom of recycling containers that are left out of doors.
• Roof gutters are easily overlooked but can produce millions of mosquitoes each season and should be cleaned as often as necessary to prevent clogging.
• Bird baths should be cleaned on a regular basis to prevent the buildup of algae and dead leaves that mosquito larvae feed on. Change the water at least weekly.
• If your pet's food and water bowls are kept outside they should be kept clean and the water changed daily.
• Turn over tools and toys, such as wheelbarrows and plastic wading pools, which can accumu-late water when not in use.
• Ensure that any potted plants that are kept out of doors are draining properly and that they do not maintain standing water.
• Keep backyard swimming pools clean and chlorinated. Arrange with a neighbor or friends to maintain your pool if you are away from home for an extended period of time such as on vacation.
• Remember that the water that collects on top of a swimming pool cover may prove to be an excellent breeding area for mosquitoes.
• Ornamental pools can become major mosquito producers if they are allowed to stagnate.
  Aerate the pools or stock them with surface feeding minnows [Goldfish offer little, if any, benefit].
• Eliminate low lying areas where standing water may collect.
• Mow your lawn on a regular basis.
• Cut weeds growing next to building foundations and fence lines in order to remove mosquito hiding and resting areas.

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Remedies with Limited Value in Mosquito Control

Remember that area spraying of adult mosquitoes is only a temporary solution.

While "Bug Zappers" are very popular with home owners, their overall effectiveness is questionable since mosquitoes are attracted by the carbon dioxide given off by our bodies rather than light.

Nor, unfortunately, are bats or purple martins considered to be an effective means of controlling mosquitoes. They are opportunistic feeders and mosquitoes make up only a small percentage of their diet.

Electronic mosquito repellers have also been shown to have limited effectiveness.

CAUTION: ALWAYS REMEMBER THAT WHEN USING A PESTICIDE YOU MUST:
ONLY USE INSECTICIDES THAT ARE APPROVED FOR USE AGAINST THE SPECIFIC PEST YOU ARE TRYING TO CONTROL.

ALWAYS READ AND FOLLOW THE LABEL DIRECTIONS FOR SAFE USE.

FOR MORE INFORMATION, CONTACT:

American Mosquito Control Association
J.B. Smith Hall
176 Jones Avenue
Rutgers University
New Brunswick, NJ 08901-9536
732-932-0667

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OVERVIEW OF WEST NILE VIRUS

Q. What is West Nile encephalitis?
A. "Encephalitis" means an inflammation of the brain and can be caused by viruses and bacteria, including viruses transmitted by mosquitoes. West Nile encephalitis is an infection of the brain caused by West Nile virus, a flavivirus commonly found in Africa, West Asia, and the Middle East. It is closely related to St. Louis encephalitis virus found in the United States.

Q. Where did West Nile virus come from?
A. West Nile virus has been commonly found in humans and birds and other vertebrates in Africa, Eastern Europe, West Asia, and the Middle East, but until 1999 had not previously been documented in the Western Hemisphere. It is not known from where the U.S. virus originated, but it is most closely related genetically to strains found in the Middle East.

Q. How long has West Nile virus been in the U.S.?
A. It is not known how long it has been in the U.S., but CDC scientists believe the virus has probably been in the eastern U.S. since the early summer of 1999, possibly longer.

Q. How many cases of West Nile encephalitis in humans have occurred in the U.S. ?
A. In 1999, 62 cases of severe disease, including 7 deaths, occurred in the New York area. In 2000, 17 cases have been reported through September, including 1 death. No reliable estimates are available for the number of cases of West Nile encephalitis that occur worldwide.

Q. I understand West Nile virus was found in "overwintering" mosquitoes in the New York City area in early 2000. What does this mean?
A. One of the species of mosquitos found to carry West Nile virus is the Culex species which survive through the winter, or "overwinter," in the adult stage. That the virus survived along with the mosquitoes was documented by the widespread transmission the summer of 2000.

Q. Do the findings indicate that West Nile virus is established in the Western Hemisphere?
A. It is too early to speculate about the permanent establishment of West Nile virus. Continued surveillance will assist in answering this question.

Q. Is the disease seasonal in its occurrence?
A. In the temperate zone of the world [i.e., between latitudes 23.5° and 66.5° north and south], West Nile encephalitis cases occur primarily in the late summer or early fall. In the southern climates where temperatures are milder, West Nile virus can be transmitted year round.

Q. What precautions are needed to prevent a recurrent outbreak?
A. Active sampling for West Nile virus [i.e., surveillance] in mosquito and bird populations will greatly enhance state and local governments' early detection systems. When the first virus activity is detected in a community, prior to the occurrence of human disease, rapid mosquito control measures, such as targeted application of adulticides and larvacides, should be implemented.

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TRANSMISSION OF WEST NILE VIRUS

Q. How do people get West Nile encephalitis?
A. By the bite of mosquitoes infected with West Nile virus.

Q. What is the basic transmission cycle?
A. Mosquitoes become infected when they feed on infected birds, which may circulate the virus in their blood for a few days. Infected mosquitoes can then transmit West Nile virus to humans and animals while biting to take blood. The virus is located in the mosquito's salivary glands. During blood feeding, the virus may be injected into the animal or human, where it may multiply, possibly causing illness.

Q. If I live in an area where birds or mosquitoes with West Nile virus have been reported and a mosquito bites me, am I likely to get sick?
A. No. Even in areas where mosquitoes do carry the virus, very few mosquitoes—much less than 1%—are infected. If the mosquito isinfected, less than 1% of people who get bitten and become infected will get severely ill. The chances you will become severely ill from any one mosquito bite are extremely small.

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Q. Can you get West Nile encephalitis from another person?
A. No. West Nile encephalitis is NOT transmitted from person-to-person. For example, you cannot get West Nile virus from touching or kissing a person who has the disease, or from a health care worker who has treated someone with the disease.

Q. Is a woman's pregnancy at risk if she gets West Nile encephalitis?
A. There is no documented evidence that a pregnancy is at risk due to infection with West Nile virus.

Q. Besides mosquitoes, can you get West Nile virus directly from other insects or ticks?
A. Infected mosquitoes are the primary source for West Nile virus. Although ticks infected with West Nile virus have been found in Asia and Africa, their role in the transmission and maintenance of the virus is uncertain. However, there is no information to suggest that ticks played any role in the cases identified in the United States.

Q. How many types of animals have been found to be infected with West Nile virus?
A. Although the vast majority of infections have been identified in birds, through September 2000 CDC has received reports of WN virus infection in horses, cats, bats, chipmunks, skunks, squirrels, domestic rabbits, and raccoons.

Q. Can you get West Nile virus directly from birds?
A. There is no evidence that a person can get the virus from handling live or dead infected birds. However, persons should avoid bare-handed contact when handling any dead animals and use gloves or double plastic bags to place the carcass in a garbage can.

Q. Can I get infected with West Nile virus by caring for an infected horse?
A. West Nile virus is transmitted by infectious mosquitoes. There is no documented evidence of person-to-person or animal-to-person transmission of West Nile virus. Normal veterinary infection control precautions should be followed when caring for a horse suspected to have this or any viral infection.

Q. How does West Nile virus actually cause severe illness and death in humans?
A. Following transmission by an infected mosquito, West Nile virus multiplies in the person's blood system and crosses the blood-brain barrier to reach the brain. The virus interferes with normal centralnervous system functioning and causes inflammation of brain tissue.

Q. What proportion of people with severe illness due to West Nile virus die?
A. Among those with severe illness due to West Nile virus, case-fatality rates range from 3% to 15% and are highest among the elderly. Less than 1% of those infected with West Nile virus will develop severe illness.

Q. If a person contracts West Nile virus, does that person develop a natural immunity to future infection by the virus?
A. It is assumed that immunity will be lifelong; however, it may wane in later years.

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PREVENTION OF WEST NILE VIRUS

Q. Is there a vaccine against West Nile encephalitis?
A. No, but several companies are working towards developing a vaccine.

Q. What can I do to reduce my risk of becoming infected with West Nile virus?
A. Stay indoors at dawn, dusk, and in the early evening.

• Wear long-sleeved shirts and long pants whenever you are outdoors.
• Spray clothing with repellents containing permethrin or DEET since mosquitoes may bite through thin clothing.
• Apply insect repellent sparingly to exposed skin. An effective repellent will contain 35% DEET [N,N-diethyl-meta-toluamide]. DEET in high concentrations [greater than 35%] provides no additional protection.
• Repellents may irritate the eyes and mouth, so avoid applying repellent to the hands of children.
• Whenever you use an insecticide or insect repellent, be sure to read and follow the manufacturer's DIRECTIONS FOR USE, as printed on the product.
• Note: Vitamin B and "ultrasonic" devices are NOT effective in preventing mosquito bites.

Q. Where can I get more information on mosquito repellents?
A. Visit the American College of Physicians Web site: "Mosquitoes and mosquito repellents: A clinician's guide" [Mark S. Fradin, MD. Annals of Internal Medicine. June 1, 1998;128:931-940]. You can also find information on insect repellents containing DEET at the Environmental Protection Agency [EPA] Web site.

Q. Where can I get information about the use of pesticide sprays that are being used for mosquito control?
A. The federal agency responsible for pesticide evaluation is the Environmental Protection Agency [EPA]. See their Web site for detailed answers to the questions about pesticides used for mosquito control.

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SYMPTOMS OF WEST NILE VIRUS

Q. Who is at risk for getting West Nile encephalitis?
A. All residents of areas where virus activity has been identified are at risk of getting West Nile encephalitis; persons older than 50 years have the highest risk of severe disease.

Q. What are the symptoms of West Nile encephalitis?
A. Most infections are mild, and symptoms include fever, headache, and body aches, occasionally with skin rash and swollen lymph glands. More severe infection may be marked by headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, paralysis, and, rarely, death.

Q. What is the incubation period in humans [i.e., time from infection to onset of disease symptoms] for West Nile encephalitis?
A. Usually 3 to 15 days.

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Testing and Treating West Nile Encephalitis in Humans

Q. I think I have symptoms of West Nile virus. What should I do?
A. Contact your health care provider if you have concerns about your health. If you or your family members develop symptoms such as high fever, confusion, muscle weakness, and severe headaches, you should see your doctor immediately.

Q. How do health care providers test for West Nile virus?
A. Your physician will first take a medical history to assess your risk for West Nile virus. People who live in or traveled to areas where West Nile virus activity has been identified are at risk of getting West Nile encephalitis; persons older than 50 years of age have the highest risk of severe disease. If you are determined to be at high risk and have symptoms of West Nile encephalitis, your provider will draw a blood sample and send it to a commercial or public health laboratory for confirmation.

Q. How is West Nile encephalitis treated?
A. There is no specific therapy. In more severe cases, intensive supportive therapy is indicated, often involving hospitalization, intravenous fluids, airway management, respiratory support [ventilator], prevention of secondary infections [pneumonia, urinary tract, etc.], and good nursing care.

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WEST NILE VIRUS AND BIRDS

Q. Do birds infected with West Nile virus die or become ill?
A. In the 1999 New York area epidemic, there was a large die-off of American crows. Through September 2000, West Nile virus has been identified in at least 70 species of birds found dead in the United States. Most of these birds were identified through reporting of dead birds by the public.

Q. How can I report a sighting of dead bird[s] in my area?
A. Click here to fill out an online form to report a dead bird.

WEST NILE VIRUS AND DOGS AND CATS

Q. Can West Nile virus cause illness in dogs or cats?
A. There is a published report of West Nile virus isolated from a dog in southern Africa [Botswana] in 1982. West Nile virus has been isolated from several dead cats in 1999 and 2000. A serosurvey of dogs and cats in the epidemic area showed a low infection rate.

Q. Can infected dogs or cats be carriers [i.e., reservoirs] for West Nile virus and transmit the virus to humans?
A. West Nile virus is transmitted by infectious mosquitoes. There is no documented evidence of person-to-person, animal-to-animal, or animal-to-person transmission of West Nile virus. Veterinarians should take normal infection control precautions when caring for an animal suspected to have this or any viral infection.

Q. How do dogs or cats become infected with West Nile virus?
A. The same way humans become infected—by the bite of infectious mosquitoes. The virus is located in the mosquito's salivary glands. During blood feeding, the virus is injected into the animal. The virus then multiplies and may cause illness. Mosquitoes become infected when they feed on infected birds, which may circulate the virus in their blood for a few days. It is possible that dogs and cats could become infected by eating dead infected animals such as birds, but this is unproven.

Q. Can a dog or cat infected with West Nile virus infect other dogs or cats?
A. No. There is no documented evidence that West Nile virus is transmitted from animal to animal.

Q. How long can a dog or cat be infected with West Nile virus?
A. The answer is not known at this time.

Q. Should a dog or cat infected with West Nile virus be destroyed? What is the treatment for an animal infected with West Nile virus?
A. No. There is no reason to destroy an animal just because it has been infected with West Nile virus. Full recovery from the infection is likely. Treatment would be supportive and consistent with standard veterinary practices for animals infected with a viral agent.

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WEST NILE VIRUS AND HORSES

Q. Has West Nile virus caused severe illness or death in horses?
A. Yes, while data suggest that most horses infected with West Nile virus recover, results of investigations indicate that West Nile virus has caused deaths in horses in both the 1999 outbreak and in 2000.

Q. How do the horses become infected with West Nile virus?
A. The same way humans become infected—by the bite of infectious mosquitoes. The virus is located in the mosquito's salivary glands. When mosquitoes bite or "feed" on the horse, the virus is injected into its blood system. The virus then multiplies and may cause illness. The mosquitoes become infected when they feed on infected birds or other animals.

Q. How does the virus cause severe illness or death in horses?
A. Following transmission by an infected mosquito, West Nile virus multiplies in the horse's blood system, crosses the blood brain barrier, and infects the brain. The virus interferes with normal central nervous system functioning and causes inflammation of the brain.

Q. Can I get infected with West Nile virus by caring for an infected horse?
A. West Nile virus is transmitted by infectious mosquitoes. There is no documented evidence of person-to-person or animal-to-person transmission of West Nile virus. Normal veterinary infection control precautions should be followed when caring for a horse suspected to have this or any viral infection.

Q. Can a horse infected with West Nile virus infect horses in neighboring stalls?
A. No. There is no documented evidence that West Nile virus is transmitted between horses. However, horses with suspected West Nile virus should be isolated from mosquito bites, if at all possible.

Q. My horse is vaccinated against eastern equine encephalitis [EEE], western equine encephalitis [WEE], and Venezuelan equine encephalitis [VEE]. Will these vaccines protect my horse against West Nile virus infection?
A. No. EEE, WEE, and VEE belong to another family of viruses for which there is no cross-protection. There is no approved vaccine currently available for West Nile virus.

Q. How long will a horse infected with West Nile virus be infectious?
A. We do not know if an infected horse can be infectious [i.e., cause mosquitoes feeding on it to become infected]. However, previously published data suggest that the virus is detectable in the blood for only a few days.

Q. What is the treatment for a horse infected with West Nile virus? Should it be destroyed?
A. There is no reason to destroy a horse just because it has been infected with West Nile virus. Data suggest that most horses recover from the infection. Treatment would be supportive and consistent with standard veterinary practices for animals infected with a viral agent.

Q. Where can I get more information on horses and West Nile virus?
A. Visit the USDA Web site Animal and Plant Inspection Service [APHIS].

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WEST NILE VIRUS AND WILD GAME HUNTERS

Q. Are duck and other wild game hunters at risk for West Nile virus infection?
A. Because of their outdoor exposure, game hunters may be at risk if they become bitten by mosquitoes in areas with West Nile virus activity. The extent to which West Nile virus may be present in wild game is unknown. Surveillance studies are currently underway in collaboration with the U.S. Geological Survey [USGS] National Wildlife Health Center [in Madison, Wisconsin] and with state and local wildlife biologists and naturalists to answer this question.

Q. What should wild game hunters do to protect against West Nile virus infection?
A. Hunters should follow the usual precautions when handling wild animals. If they anticipate being exposed to mosquitoes, they should apply insect repellents to clothing and skin, according to label instructions, to prevent mosquito bites. Hunters should wear gloves when handling and cleaning animals to prevent blood exposure to bare hands and meat should be cooked thoroughly.

Q. Who should wild game hunters contact for information about the risk for West Nile virus infection in specific geographic areas?
A. Hunters should check with their local area department of wildlife and naturalist resources, state epidemiologist at the state health department, or the U.S. Geological Survey [USGS] National Wildlife Health Center,Madison, WI, 608-270-2400 for information on local area risk.

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