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Our District Conservationist, Pat Larr, retired December 3, 2009, after 35 years of service. We wish Pat good luck in her future endeavors, and we will be maintaining the articles she wrote here. Contained in them are answers to questions Pat received repeatedly on conservation and natural resources topics. We hope they provide you with a better understanding of our natural resources and what can be done to conserve them.

Pat's Archive

Much public concern, debate, and confusion has arisen over the past few years over the spread of West Nile virus: concern over illnesses and deaths resulting from it, debate over how to control it, and some confusion in the general public over how it it's contracted. Hopefully, the information I'll give here will clarify things a bit.

What is West Nile Virus (WNV)?

It is a mosquito-borne virus first discovered in the West Nile District of Uganda in 1937. WNV spread across areas of Africa, Eastern Europe, West Asia, and the Middle East, eventually appearing in the Eastern United States in 1999. Although the exact origin of the WNV found in the United States remains unknown, the strain isolated from the 1999 outbreak is most closely related to that identified in Israel in 1998 from a dead goose.

Is it prevalent in Indiana?

  • The first positive indicator in Indiana was a dead crow found on August 21, 2001, in Marion County.
  • The first human case was identified almost one year later on August 9, 2002, in a 46-year-old Wabash County resident.
  • As of August 21, 2003, 4 probable human and 1 horse case, 33 mosquito groups, 12 presumptive positive live birds, and 21 dead birds have been reported.

What's been done to control WNV?

In Southern Indiana, the Clark and Floyd County Health Departments, with assistance from Indiana University Southeast, have initiated a West Nile virus mosquito surveillance project. Students place traps around the counties to collect the insects, which are then inspected and tested in an IUS lab. Instead of waiting weeks to receive test results from the state lab and to find out whether the virus is being carried by insects in a certain area, results are known immediately. Mosquito populations where the virus is found can then be attacked quickly.

The general public also plays an important role in eradication of the infected mosquitos. Reporting areas of mosquito populations helps local health departments in their efforts to control them. In return, health departments have tried to educate the public about the whys and wherefores of West Nile.

Can WNV be spread by contact with a person/animal that has it?

No. As I mentioned above, it is a mosquito-borne virus. It is spread by the bite of an infected mosquito. It's important to understand that not all mosquitos carry the virus; note, I said the bite of an infected one.

Humans and domestic mammals are considered "dead-end" hosts, who do not contribute to the transmission cycle, but can develop an illness because of infection. Most people who become infected will not have any type of illness. It's estimated about 20% will develop mild symptoms of West Nile fever that include fever, headache and body aches, occasionally a skin rash on the trunk of the body, and swollen lymph glands. Those people that develop a more severe form of the disease (1 in 150 persons) will show signs of headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, and paralysis.

Is there a certain species of mosquito that carries the virus?

The mosquito most closely associated with transmitting West Nile virus in the United States, and in Indiana, is the Northern House Mosquito (Culex pipiens). The larvae of this species prefer to live in nutrient-rich, organic (often polluted) sites, such as leakage from septic tanks, abandoned swimming pools, clogged gutters, and similar enriched-water containers.

When you're out on your back porch in the evening, you may think that the neighborhood mosquitos instinctively attack any human in force. This is not necessarily the case. Culex is selective of its host. It prefers birds, and after feeding on a bird, will seek out another bird rather than a person or other mammal. Culex are generally weak fliers and do not move far from home, although they have been known to fly up to two miles.

Mosquitos acquire WNV when feeding on infected birds that have high levels of WNV in their blood. The virus is then stored in the mosquito's salivary glands and transmitted to humans or other animals when the mosquito bites.

What can the average person do to help fight mosquitos?

There are many ways you can prevent being bitten by mosquitos and reduce mosquito-breeding areas around your home. Before I get into what you can do to help, however, let me talk a little bit about mosquitos' habitats and life cycle. This will give you a better insight into the prevention measures.

There are about 200 species of mosquitos found in the United States, each with their own habitat, unique behavior, and host they prefer. Despite their differences, all mosquitos share some common traits, one of which is as a four-stage life cycle.

Egg - female mosquitos lay their eggs directly on the surface of stagnant water;

Larva - the eggs hatch and a mosquito larva or "wriggler" emerges. The larva lives in the water, feeds, and develops into the third stage of the life cycle;

Pupa - the pupa or "tumbler" lives in the water but does not feed;

Adult - the mosquito emerges from the pupal case in the water as a fully developed adult. It flies a short time after when its body parts have hardened.

 

Mosquitos lay their eggs in standing water. Although the location of the water varies among species, the fact that it is stagnant does not. Lakes, streams are usually relatively free of mosquito larvae due to the natural predators they support. Insects, wildlife (including birds such as swallows and ducklings, and bats), and fish eat immature mosquitos (larvae) in the water, or eat flying adults. Frogs, salamanders, and many aquatic insects such as water striders, damselflies, and dragonflies also feed on mosquitos.

Wetland areas have created some controversy in discussions of mosquito control. Before reading on, you may want to read Pats Page - What is a wetland? for an explanation of what a wetland is and does. Contrary to what some may believe, healthy wetland areas are relatively free of mosquitos just as lakes and streams are and for the same reason; they are home to many mosquito-eating predators. O.k. Note again that I said healthy. Problems arise when storm water runoff and incompatible surrounding land use practices adversely affect natural wetlands. This includes storm water runoff from urban and newly urbanizing areas and sediment from both agriculture and construction activities. As a result, these wetlands often have stagnant water, increased nutrient levels, and few natural mosquito predators - essentially, all the things mosquitos love.

Some mosquito control programs have recommended draining wetlands in order to control mosquitos. This solution can backfire, however. As I've explained, mosquitos do require standing water to breed, but they also have a very short life cycle (4 days to a month), and the eggs can remain dormant for more than a year. Therefore, even after a wetland is drained, it may still hold enough water after a rain to breed mosquitos. In fact, it may produce more mosquitos than before because it can no longer support natural mosquito predators.

Enough said about the mosquitos themselves, let's move on to preventative actions you can take against mosquitos and West Nile. Keep in mind that:

  • Mosquitos breed in standing water.
  • Any place where water stands for more than a week is sufficient to breed mosquitos.
  • Eliminating mosquito habitat on your property is the primary method of minimizing mosquito population booms.

You can take the following steps to reduce mosquito-breeding opportunities around your home:

  • Eliminate or empty any artificial water-collecting containers such as unused buckets, water troughs, and wheelbarrows, when not in use.
  • Clean out house roof gutters.
  • Clean bird baths and animal water bowls at least once a week.
  • Empty plant pots or drip trays at least once a week.
  • Get rid of unused tires, or keep them under cover, so they do not collect water. In 2002, the Fort Wayne/Allen County Department of Health surveyed mosquito-breeding sites near human West Nile virus cases. The survey found that 66% of these breeding sites were TIRES.
  • Clean and chlorinate outdoor swimming pools, saunas and hot tubs. If not in use, keep empty and covered.
  • Check for standing water below air conditioner drain outlets and outdoor faucets.
  • Drain and cover boats.
  • Check for standing water especially after any rain, watering the lawn or garden, or after washing the car.
  • Drain culverts and ditches containing stagnant water.
  • Drain or cover old cisterns.
  • Level the ground around your home so water can run off or be absorbed evenly and not collect in low spots.
  • Fill or drain tire ruts.
  • Check for soggy areas over septic absorption fields.

To reduce your contact with mosquitos, you can:

  • Use a mosquito repellent that contains DEET (N, N-diethyl-meta-toluamide). Be sure to follow label directions.
  • Wear clothing that covers the skin such as long sleeve shirts and pants when out after dusk or in shaded areas during the daytime.
  • Reduce outside activity during dawn and dusk when mosquitos are actively feeding.
  • Make sure that doors and windows have tight-fitting screens. Repair or replace all screens that have tears or holes.
  • Use the proper type of light outside; incandescent lights attract mosquitos, whereas fluorescent lights to not (they don't repel them either).
  • Be aware that crowds or other "mass gatherings" give off large amounts of carbon dioxide, which can attract more mosquitos from a greater distance.
  • Vitamin B and "ultrasonic" devices are NOT effective in preventing mosquito bites.

Things you think might help, but may not:

Mosquito fish. Some county mosquito-control programs distribute mosquito fish as a means of control. C. pipiens normally thrive in artificial containers, so this may be somewhat effective in ornamental ponds. However, if wetland areas they can be detrimental. Most Indiana wetlands that will support fish are often already inhabited by insect-eating fish as effective as mosquito fish. Studies indicate that mosquito fish will feed on naturally occurring mosquito predators such as amphibians and reptiles.

Bug Zappers. Studies have shown that bug zappers are relatively ineffective to control mosquitos around the home. In fact, you're more likely to be bitten by a mosquito in the vicinity of a zapper. Bug zappers kill more insect predators and parasites than biting insects, and release insect-borne bacteria and viruses as they do so. They also release insect particles that are potential allergens and/or cause various respiratory conditions such as asthma.

 

Keep in mind that West Nile virus is new to North America and there are still many unknowns. As scientific research continues, information is constantly changing. It's best to keep updated on the most current information to effectively control the mosquitos and combat the virus. The following list of agencies and resources have a store of useful, up-to-date information to help you.

Centers for Disease Control and Prevention (CDC) - West Nile Virus Basics

What do I do if I find a dead bird?

Don't handle it! In Indiana, if you find a dead blue jay, crow, falcon, or hawk, contact your local health department and ask them if they would like to pick it up and send it to the State Laboratory. The Clark County Health Department is located at 1216 Akers Ave., Jeffersonville, IN, and may be reached at (812) 282-7521.

Blue jays, crows, falcons, and hawks are highly sensitive to the virus, and therefore are the best indicators of West Nile virus activity in a community. They are the only species of birds that the State Laboratory is testing for the virus.

If you need to dispose of a dead bird, don't handle it with your bare hands. Use gloves or a plastic bag turned inside out over your hand to pick up the bird and dispose of it in the trash.

What is DEET?

DEET (N, N-diethyl-meta-toluamide) is the active ingredient in many insect repellent products. It is used to repel biting pests such as mosquitoes and ticks, including ticks that may carry Lyme disease. Studies indicate that DEET repels ticks for about three to eight hours, depending on the percentage of the chemical in the product. Products containing DEET are available to the public in a variety of liquids, lotions, sprays, and impregnated materials (such as wrist bands). It was designed for direct application to human skin to repel insects rather than kill them. Always follow label directions when using a product containing DEET.