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How
Mosquitoes Work It's summer time. You're out in your backyard enjoying the sun and grilling your dinner. Ouch! You look down at your arm and see a painful, swelling mosquito bite. Moments later, you feel another one bite you. What are these pesky insects? Why do they bite? Do they carry diseases? What can you do to protect yourself?
In
this edition of HowStuffWorks, we'll take a close-up look at mosquitoes
-- how they breed,
The word "mosquito" is Spanish for "little fly," and its use dates back to about 1583 in North America (Europeans referred to mosquitoes as "gnats"). Mosquitoes belong to the order Diptera, true flies. Mosquitoes are like flies in that they have two wings, but unlike flies, their wings have scales, their legs are long and the females have a long mouth part (proboscis) for piercing skin. Mosquitoes are insects that have been around for over 30 million years. And it seems that, during those millions of years, mosquitoes have been honing their skills so that they are now experts at finding people to bite. A mosquito has a battery of sensors designed to track their prey, including: Chemical sensors -- mosquitoes can sense carbon dioxide and lactic acid up to 100 feet (36 meters) away. Just about any mammal or bird gives off these gases as part of its normal breathing. Certain chemicals in sweat also seem to attract mosquitoes (people who don't sweat don't get nearly as many mosquito bites). Visual sensors -- if you are wearing clothing that contrasts with the background, and especially if you move while wearing that clothing, mosquitoes can see you and zero in on you. It's a good bet that anything moving is "alive", and therefore full of blood, so this is a good strategy. Heat sensors -- Mosquitoes can detect heat, so they can find warm-blooded mammals and birds very easily once they get close enough. Something with this many sensors sounds more like a military aircraft than an insect. That's why mosquitoes are so good at finding and biting you! As we'll see later, one of the only ways to stop mosquitoes from finding you is to confuse their chemical receptors with something like DEET. Like all insects, adult mosquitoes have three basic body parts: Head - This is where all the sensors are, along with the biting aparatus. The head has two compound eyes, antennae to sense chemicals and the mouth parts called the palpus and the proboscis (only females have the probiscus, for biting). Thorax - This segment is where the two wings and six legs attach. It contains the flight muscles, compound heart, some nerve cell ganglia and trachioles. Abdomen - This segment contains the digestive and excretory organs. The parts of a mosquito There are over 2,700 species of mosquitoes in the world, and there are 13 mosquito genera (plural for "genus") that live in the United States. Of these genera, most mosquitoes belong to three:
Aedes
- These are sometimes called "floodwater" mosquitoes because
flooding is important for their eggs to hatch. Aedes mosquitoes
have abdomens with pointed tips. They include such species as the
yellow-fever mosquito (Aedes aegypti) and the Asian tiger mosquito
(Aedes albopictus). They are strong fliers, capable of travelling
great distances (up to 75 miles/121 km) from their breeding sites.
They persistently bite mammals (especially
Anopheles - These tend to breed in bodies of permanent fresh water. Anopheles mosquitoes also have abdomens with pointed tips. They include several species, such as the common malaria mosquito (Anopheles quadrimaculatus), that can spread malaria to humans. Culex - These tend to breed in quiet, standing water. Culex mosquitoes have abdomens with blunt tips. They include several species such as the northern house mosquito (Culex pipiens). They are weak fliers and tend to live for only a few weeks during the summer months. They persistently bite (preferring birds over humans) and attack at dawn or after dusk. Their bite is painful. Some mosquitoes, such as the cattail mosquito (Coquilettidia perturbans), are becoming more prevalent pests as humans invade their habitats. Let's examine how mosquitoes live and breed.
Life
Cycle and Breeding
Larva The mosquito eggs hatch into larvae or "wigglers," which live at the surface of the water and breathe through an air tube or siphon. The larvae filter organic material through their mouth parts and grow to about 0.5 to 0.75 inches (1 to 2 cm) long; as they grow, they shed their skin (molt) several times. Mosquito larvae can swim and dive down from the surface when disturbed (see Mosquito Life Cycle for a Quicktime movie of free-swimming Asian tiger mosquito larvae). The larvae live anywhere from days to several weeks depending on the water temperature and mosquito species.
Pupa
Adult One of the first things that adult mosquitoes do is seek a mate, mate and then feed. Male mosquitoes have short mouth parts and feed on plant nectar. In contrast, female mosquitoes have a long proboscis that they use to bite animals and humans and feed on their blood (the blood provides proteins that the females need to lay eggs). After they feed, females lay their eggs (they need a blood meal each time they lay eggs). Females continue this cycle and live anywhere from many days to weeks (longer over the winter); males usually live only a few days after mating. The life cycles of mosquitoes vary with the species and environmental conditions.
Mosquito
Bites
Photo
courtesy Centers for Disease Control & Prevention, photographer
Jim Gathany If she is disturbed, she will fly away. Otherwise, she will remain until she has a full abdomen. If you were to cut the sensory nerve to her abdomen, she would keep sucking until she burst. After she has bitten you, some saliva remains in the wound. The proteins from the saliva evoke an immune response from your body. The area swells (the bump around the bite area is called a wheal), and you itch, a response provoked by the saliva. Eventually, the swelling goes away, but the itch remains until your immune cells break down the saliva proteins. To treat mosquito bites, you should wash them with mild soap and water. Try to avoid scratching the bite area, even though it itches. Some anti-itch medicines such as Calamine lotion or over-the-counter cortisone creams may relieve the itching. Typically, you do not need to seek medical attention (unless you feel dizzy or nauseated, which may indicate a severe allergic reaction to the bite).
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Often called "punkies", "no-see'ums" or sand flies, the biting midges are viscious where they occur. They are often more troublesome than mosquitoes because they can easily enter dwellings through ordinary 16-mesh window screen. The presence of these insects can decrease property values and severly hamper use of recreational areas. Vacationers and campers literally have been driven away from areas by these tiny biters. Snad flies can also cause loss to cattlemen in terms of annoyance to cattle and transmission of various nematode diseases. Sand flies are members of the insect order Diptera and undergo a complete development with egg, larva, pupa, and adult forms. The adults are less than 1/16-inch long, dark gray to black in color. and have one pair of wings, which are spotted. The sand flies breed predominantly in salt marshes; however some species that are found inland breed in fresh water areas and tree holes. Larvae of sand flies are found in mud, sand, and deris around the edges of ponds, springs, lakes, creeks, and in tree holes or slime covered bark. In the water they are free swimmers and are commonly found on floating twigs or leaf trash. The larvae pupate on floating debris or at the water's edge. The adult females, like mosquitoes, require blood to mature the eggs. Males do not bite. Sand fly larvae can be found in marshes the year-round; however, the period of greatest adult activity is June to August. Sand fly activity is associated with air movement. Adults of most species seldom bite when there is air movement. Sand flies are also sensitive to temperature. Animals having high body temperature are attractive to great numbers of female sand flies. Persons performing hard labor out-of-doors frequently are severely annoyed by these insects. |
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A
SINGLE FLY CAN CONTAMINATE FEED/FOOD The fly is an enemy because it is one of the biggest disease carriers in existance. Moist, warm, decaying material protected by sunlight is favored for fly eggs to hatch and in only 8 short hours for fly larvae or maggots to grow. An uncovered garbage can is an ldeal breeding place. Flies feed and reproduce on filth, decaying matter, and water. Flies are tranmitters of disease primarily because they feed on human and animal wastes. The dangerous bacteria present in these wastes stick to the mouth, footpads and hairs of flies and may then be deposited in feed intended for animal consumption. Fly feces, which contain disease-bearing organisms, can also contaminate human food. Flies defecate every four to five minutes. And since flies have no teeth and must take their nourishment in liquid form, they spit on solid food and let the dissolve before consuming it. Fly spittle, or vomitus, is swarming with bacteria and contaminates feed and areas where feed is stored. A fly can infect feed/food by merely landing on it. Flies can enter a building that has openings not much larger than the head of a pin. Although they rarely travel very far from where they are hatched, flies may be lured to the sources of attractive odors. Flies may also be carried long distances by air current. One female fly can produce thousands of offspring in a single breeding season. flies have favorite resting places. They are especially fond of places protected from the wind and on edges such as garbage can rims and electric wires Flies carry bacteria that can cause many diseases known and unknown to man. One fly can carry over 33 million disease-causing microorganisms on the inner and outer surfaces of its body. There are over 87,000 different fly species. The fly is one of the fastest flying insects. A fly's vision is sharp for only 24 to 36 inches. One successful hatch can result in well over 2 million flies. One season can breed as much as 25 generations. |
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Aug 14, 2002 Florida
Reports 1st Human Case Of West Nile TAMPA - Health officials confirmed the first human case of West Nile virus in Florida on Tuesday and expanded a health alert to four more counties, including Sumter and Orange, bringing the total to six. The newest alert also covers Lake and Marion counties. The Sumter County man who tested positive for the mosquito-borne virus may have been bitten in Louisiana, where 85 people have contracted West Nile and seven have died. "We don't know for sure,'' said April Crowley, spokeswoman for the state Department of Health. Earlier this week, a dead crow found five miles west of Brooksville in Hernando County tested positive for West Nile. Last week, the Department of Health issued medical alerts for Escambia and Volusia counties. The alerts are issued to advise people the virus is present in their counties so that they can avoid mosquito bites, and also to prompt doctors to be more aware of potential cases. The virus previously occurred in Africa, the Middle East, western Asia and Europe. It was first discovered in this country in 1999. The disease spreads when mosquitoes bite infected birds and then bite a person. Humans cannot spread the disease. Health officials test dead birds, horses and chickens kept in outdoor cages to monitor several mosquito-borne diseases including West Nile and eastern equine encephalitis. Although Sumter was the only county in the newest list of counties put under alert with a human case, birds, horses and chickens in the other three have tested positive for West Nile. In Lake County, two birds and three horses have been found with the virus. Marion had six horses and one bird. Orange had nine chickens, a horse and two birds, and Sumter had one horse. No animal cases of West Nile have been found in Hillsborough, but eight chickens have tested positive for the virus in Pinellas and one bird in Pasco. To the south, Manatee has had a horse and a chicken with the disease. Only about 10 percent of people bitten by infected mosquitoes show any symptoms, which are similar to the flu. Only about 1 in 200 people develop encephalitis, a potentially fatal swelling of the brain. So far this year, fewer people have contracted West Nile in Florida than in 2001. "Last year by this time, we had three human cases. We're seeing a little more animal cases this year,'' Crowley said. |
| June
15, 2002
First
West Nile Case of the Year Pinellas County is dealing with their first West Nile virus case of the year. It didn’t come as a surprise to Pinellas County Mosquito Control when a sentinel chicken tested positive for the virus. Nancy Page with mosquito control says, she knew it was a matter of time. "We were expecting it eventually." she says. "We had it come up last year in November (and) it was spreading throughout the state this year, so we knew it would arise in Pinellas county again this year." The chicken came from a St. Petersburg coop, which is one of the best weapons in detecting mosquito-born diseases like WEST NILE. Pinellas County Mosquito Control has eight chicken coops across the county that test the blood from sentinel chickens each week. Wednesday, one of these samples tested positive. WEST NILE is transmitted from birds to mosquitoes, who can then pass it on to humans. The virus first showed up in the U.S. in New York in 1999. Two years later, Florida had its first case. While scientists don't know a lot about WEST NILE, aerial spraying and fogging to control the mosquito population seems to be the best way to fight it. Looking for recorded information on Florida cases of the West Nile virus? Call the Department of Health Bureau of Epidemiology's Arboviral Encephalitis and West Nile virus hotline at 1-888-880-5782. |
| Sunday,
March 31, 2002 Polk County Horse Tests Positive For West Nile Virus The
disease is spread primarily through infected mosquitoes. |
| Diseases:
Mosquitoes
can carry many types of diseases that are caused by bacteria, parasites
or viruses. These diseases include: • Encephalitis - Encephalitis is caused by viruses that are transmitted by mosquitoes such as the Aedes mosquitoes or Culiseta mosquitoes. The symptoms of encephalitis include high fever, stiff neck, headache, confusion and laziness/sleepiness. There are several types of encephalitis that can be transmitted by mosquitos, including St. Louis, Western equine, Eastern equine, La Crosse and West Nile. West Nile encephalitis is on the rise in the eastern United States, which has raised concerns about mosquito control (see Overview of West Nile Virus for more information). • Dengue Fever - Dengue fever is transmitted by the Asian tiger mosquito, which is native to East Asia and was found in the United States in 1985. It is also transmitted by Aedes aegypti in the tropics. Dengue fever is caused by a virus that produces a range of illnesses, from viral flu to hemorrhagic fever. It is especially dangerous for children (see Dengue Fever & Dengue Hemorrhagic Fever for more information).
------------------------------------------------------------------ WEST NILE VIRUS HITS FLORIDA Its just a short time before the VIRUS spreads further. NOW!! is the time to protect your horses, cattle, poultry and children from this potentially deadly virus WEST NILE VIRUS & ENCEPHALITIS FACT SHEET What is West Nile encephalitis? "Encephalitis" is 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. It is closely related to St. Louis encephalitis virus found in the United States. How long has West Nile virus been in the United States and where did it come from? It is not known how long it has been In the U.S. CDC scientists believe the virus has been in the eastern U.S. since the early summer of 1999, possibly longer. 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 has not previously been documented in the Western Hemisphere, It is not known from where the U.S. virus originated. In the Temperate Zone of the world (i.e., between latitudes 23.5 and 66.5 degrees 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 ran be transmitted year round. What
Is the incubation period in humans (or time from infection to onset
of disease Usually 5 to 15 days. What are the symptoms of West Nile encephalitis? Mild infections have symptoms that include fever, headache, and body aches, often 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. If you believe you have West Nile, seek medical care as soon as possible. Is a woman's pregnancy at risk if she gets West Nile encephalitis? There
is NO documented evidence that a pregnancy is at risk due to infection
with West Nile How do people get West Nile encephalitis? The bite of a mosquito that is infected with West Nile virus is all it takes to transmit the infection. Mosquitoes become infected when they feed on infected birds. After an incubation period of 1 to 2 weeks, infected female mosquitoes can then transmit West Nile virus to humans and animals while biting. The mosquitoes and the bites they cause do not differ from those bites of an uninfected mosquito. Can you get West Nile encephalitis from an infected person or an infected bird? 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. There is NO evidence that a person can get the virus from handling live or dead infected birds. However, avoid contact with any dead bird or animal, by using gloves or plastic bags to place it in a garbage can. Can you get West Nile virus directly from other insects or animals? 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 transmitted West Nile virus to patients in the New York area outbreak. Infected mosquitoes are the primary source for West Nile virus and have been found to cause the recent outbreak in the New York City metropolitan area. Although other animals (e.g., horses and dogs) may become infected with West Nile Virus, there have been no reports of the disease being transmitted from the infected animal to humans or other animals. Contact a Veterinarian if you have questions about pets or other animals. How is West Nile encephalitis treated? There is NO specific therapy or vaccine for West Nile infection. In more severe cases, intensive supportive therapy is indicated which includes hospitalization. Who is at risk for getting West Nile encephalitis? All residents of areas where virus activity had been identified are at risk of getting West Nile encephalitis; persons greater than 50 years of age have the highest risk of severe disease. What can I do to reduce my risk of becoming infected with West Nile virus?
If
you are outdoors in the evening hours, wear long-sleeved shirts
and long pants. Have
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