Bites and Stings



Bites And Stings 2380
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Many insects, spiders, reptiles, and other animals can bite or sting humans. A person's reaction to bites and stings depends on the type and amount of venom (if any) injected into the bite, whether the person is allergic to the venom, and whether the biting animal was carrying a disease-causing agent.

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Infection

Vectors

Venom

Wounds

What Kinds of Animals Bite or Sting?

In addition to bites by mammals such as dogs, cats, and humans, many other animals can bite or sting people. Some animals inject venom, which is a poisonous substance, into the skin when they bite. Depending on the type of venom, a person can experience pain, itching, red bumps, nerve damage, or, rarely, death. Bites from mosquitoes and ticks also can be dangerous in places where those biters are vectors * (carriers) for diseases caused by bacteria, viruses, or parasites.

Some of the animals that sting or bite are described in the following sections. For most of these animals, the best way to prevent being bitten or stung is to avoid areas where they live or to wear protective clothing when there is the possibility of encountering them.

Insects

Mosquitoes

In many parts of the United States, mosquitoes are a summertime annoyance. Only the females among these small flying insects bite. When they bite, they inject saliva into the skin. The red itchy bump that appears at the site of the bite is an allergic reaction to the saliva. Mosquito bites go away on their own after several days. Mosquito repellent sprays help deter mosquitoes from biting, and calamine lotion or hydrocortisone cream may help ease the itching caused by bites.

In some parts of the world, certain types of mosquito can transmit diseases. For example, parasites carried by mosquitoes cause malaria and filariasis (fil-a-RY-a-sis). Mosquitoes also spread the viruses that cause dengue fever, yellow fever, and some types of encephalitis.

* vectors are animals or insects that carry diseases and transfer them from one host to another.

Chiggers

Chiggers, also called redbugs, are the larvae (immature stages) of red mites. They live in woods, pastures, and areas with high grass and weeds. Chiggers attach to a person's clothing and then move to bare skin around the tops of socks, armpits, or waistbands. There they bite the skin, inject a fluid that dissolves cells, and suck up the liquefied tissue. Chiggers cause extremely itchy bumps that can keep itching for days after the larvae are removed. Bathing and scrubbing after exposure to chiggers will kill or dislodge them, and rubbing alcohol followed by calamine lotion is said to help relieve the itching.

Fire Ants

In the United States, fire ants come in a variety of types: imported (from South America) or native, red or black. Different types live in different geographic regions, but they are most common in the southeastern states. Fire ants usually build mounds in soft soil, but sometimes they nest in the walls of buildings.

Fire ants are very aggressive and territorial. When a person or animal disturbs their nest, they swarm. Thus, many ants can sting people at once. The venom causes a painful burning sensation, hence the name "fire" ant, followed by tiny itchy white blisters. Fire ant stings can be fatal, but only to the small number of people who are allergic to their venom.

Ticks

Ticks live in woods and fields all over the United States. Their flat dark bodies are about the size of a match head. Ticks bite humans and other animals because they need blood to survive. Usually, a tick bite causes only minor itching or irritation, but ticks also spread a number of diseases with their bites, including Rocky Mountain spotted fever and Lyme disease, both of which can be very serious illnesses. If a tick is seen on the skin, tweezers should be used to pull the tick up and out of the skin. The bite should be washed with soap and water and watched for signs of infection.

Spiders

Almost all spiders have glands that contain venom, but only 20 to 30 of the 30,000 species of spider in the world are potentially dangerous to humans. Spider bites can cause pain, nausea, fever, and cramps, but the majority of bites are minor and cause only swelling, a blister, and temporary pain. The brown recluse spider and the black widow spiders are the most dangerous spiders found in the United States. Tarantulas also bite, but the bite usually is no worse than a bee sting.

The brown recluse spider is mostly found in the south central United States, in dark places like woodpiles, sheds, and barns. With legs extended, this spider can be as large as a half-dollar. Males and females look alike and vary in color from orange to brown. They are covered with short hairs and have a violin-shaped marking on their back. Brown recluse bites usually are not fatal, but the spider's venom can cause serious illness, especially for children and the elderly.

Following a bite by a brown recluse spider, the skin around the bite may quickly become warm and swollen. Within about 15 minutes the bitten person may become dizzy and sick to the stomach. Other symptoms include fever, chills, weakness, convulsions, and joint pain. After about four days, the bite area gets hard to the touch, and it takes about six to eight weeks for the body to recover. There is no known antidote for brown recluse venom, so treatment involves several medications, usually antibiotics, antihistamines, and steroids.

Anaphylactic Shock

For most people, insect bites cause pain or itching. For some people, however, insect bites can cause anaphylactic (an-a-fa-LAK-tik) shock. This is a severe allergic reaction that can be caused by insect bites or certain foods and drugs. The severity of the allergic reaction varies from person to person, but in general, this is what happens:

The reaction usually begins within minutes of being bitten or stung. To neutralize the insect's venom, a person's body releases huge amounts of chemicals called histamines, which cause the blood vessels to expand. A little bit of histamine helps to heal infected tissue and fight germs in the bloodstream, but too much lowers blood pressure and keeps the lungs from working properly.

At first, a person might begin sneezing, itching, and feeling weak, nauseated, and panicky. The chest and stomach muscles then begin to tighten. The lungs start working abnormally, making it very difficult to breathe, and the heart loses its normal rhythm, making it hard for blood to circulate as it should.

Anaphylactic shock must be treated quickly or it may cause death. A shot of a chemical called epinephrine usually is given to stimulate the heart and improve airflow through the lungs. Antihistamines and other drugs are given to counteract the allergic reaction, raise blood pressure, and increase the flow of blood.

People who know they are allergic to insect venom often learn how to use an anaphylaxis kit, which contains epinephrine and antihistamine, and they keep the kit nearby at all times.

Black widow spiders live in all parts of the United States but are most common in the warmer parts. They live in the same types of places as brown recluse spiders. Black widows are about a half inch long (not including the legs), and they can be identified by the reddish-orange hourglass shape on the belly of their black bodies.

Black widow spiders do not bite unless they are disturbed. Among black widows, only adult females bite. The juveniles and adult males are harmless. Most people who are bitten by black widows experience some swelling and redness at the bite site, followed by increasing pain for up to 48 hours. Black widow venom affects the nervous system, and it may cause cramps in the legs, arms, and chest. Other symptoms include sweating, chills, convulsions, fever, nausea, headache, and breathing difficulty. Treatment involves cleaning the bite and receiving antivenin * medicine and antibiotics. In 99 percent of the cases, complete recovery takes place within a few hours. Complications do occur occasionally in children, the elderly, or people with allergies, and in the most serious cases they may result in death.

Scorpions

Scorpions are about as long as an index finger. They have eight legs and a curled tail with a stinger on the end. There are 30 different kinds of scorpions in the United States, and they can be found all over the country. The stings of two species, both of which live in the southwestern states, can be fatal.

A scorpion's venom causes a burning feeling in the skin, followed by swelling and discoloration of the skin. About a day later, the face, mouth, and jaw muscles become hard to control. Other symptoms include nausea, vomiting, drooling, convulsions, and difficulty breathing. Scorpion bites are treated with antivenins and other medications to control muscle spasms and convulsions. In 99 percent of cases, complete recovery occurs after three days. However, if a person is particularly sensitive to the venom, and if muscle spasms begin right after the sting, then the person may die.

Bee and stinger. People who are allergic to bee stings may be taught to carry an anaphylaxis kit with them in case of a severe allergic reaction. © David M. Phillips, Visuals Unlimited.
Bee and stinger. People who are allergic to bee stings may be taught to carry an anaphylaxis kit with them in case of a severe allergic reaction.
© David M. Phillips, Visuals Unlimited.

Bees, Wasps, and Yellow Jackets

Honeybees and bumblebees are fat and round, and when they sting they leave their stinger in the skin. Wasps and yellow jackets are long and thin, and when they sting they keep their stinger and they can sting again. All of these insects inject venom into the skin, which causes pain, itching, swelling, and redness. For most people, bee stings are painful but not dangerous. However, some people are allergic to bee venom; for these people, bee stings can be fatal unless they are given medication right away. "Africanized" bees, also often called "killer" bees, are dangerous because they swarm and many bees can sting a person at once. Even nonallergic people can be killed by killer bees, but this is very rare.

* antivenin is an antibody (protein) capable of neutralizing a specific venom.

After a sting, the stinger should be scraped off the skin, as pulling it out may squeeze more venom into the bite. Ice or cold compresses may help reduce pain and swelling.

Snakes

Twenty species of poisonous snake live in the United States, and at least one type can be found in every state except Maine, Alaska, and Hawaii. Pit vipers, which include the rattlesnakes, copperheads, and cottonmouths, cause 99 percent of poisonous snake bites in the United States. Coral snakes cause the other 1 percent.

Venoms of different snake species range in toxicity, and a poisonous snake does not always release venom when it bites. The poisons in some species are mild, whereas others are neurotoxins (noor-o-TOK-sins) that may cause damage to the brain or spinal cord or cause people to stop breathing.

Any snake bite should be treated as an emergency because many people do not know what kind of snake bit them, and even nonpoisonous snakes can cause infection or an allergic reaction. Each year, up to 15 people die out of about 8,000 people bitten by poisonous snakes.

How to treat snakebites is a controversial * topic, but most doctors agree that ice packs, tourniquets * , and incisions should not be used. Bites should be washed with soap and water, the bitten area should be kept still and lower than the heart, and a doctor should be seen as soon as possible. Most bites do not occur in remote areas, so medical care is usually close by. Suction devices from snakebite kits or a bandage wrapped snugly 2 to 4 inches above the bite might slow the spread of venom until a hospital can be reached. Bites of poisonous snakes often are treated with antivenin.

Jellyfish

The oceans are home to many types of animal that bite or sting. The most familiar culprit is the jellyfish. All types of jellyfish have stinging tentacles that can cause a burning welt on a person's skin. In Australia, the sting of the box jellyfish can be fatal, but most jellyfish stings are just painful. Jellyfish such as the Portuguese man-of-war and sea nettles are common in coastal waters in the United States near the Atlantic Ocean. Avoiding contact with jellyfish while swimming can sometimes be difficult, especially when there are many of them in the water. Vinegar, calamine lotion, and antihistamines are said to help relieve the pain of stings.

* controversy means discussions with many different and opposing points of view.

* tourniquet is a device, often a bandage twisted tight around an arm or a leg, used to stop blood flow or hemorrhage.

Resources

Books

Aaseng, Nathan. Poisonous Creatures (Scientific American Sourcebooks). New York: Twenty First Century Books, 1997.

Foster, Steven, Roger Caras, Norman Arlott, and Amy Eisenberg. A Field Guide to Venomous Animals and Poisonous Plants. New York: Houghton Mifflin, 1998.

Nichol, John. Bites and Stings: The World of Venomous Animals. New York: Facts on File, 1990.

Organization

The U.S. Centers for Disease Control and Prevention, Division of Vector-Borne Infectious Diseases, 1300 Rampart Road, Colorado State University Foothills Research Campus, P.O. Box 2087, Fort Collins, CO 80522.
Telephone 970-221-6400
http://www.cdc.gov/ncidod/dvbid/dvbid.htm

See also
Animal Bites
Dengue Fever
Elephantiasis
Lyme Disease
Malaria
Rocky Mountain Spotted Fever
Yellow Fever
Zoonoses



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