INFECTIOUS DISEASE Bacterial • Lyme disease • Toxic shock syndrome • Tetanus • Strep throat • Tuberculosis • Whooping cough • Plague • Diphtheria • Typhoid fever • Cholera • Rocky Mountain spotted fever • Botulism • Ehrlichiosis • Tularemia • MRSA infection • Whipple's disease • Brucellosis

Note: All links within content go to MayoClinic.com

In 1975, unusually large numbers of children in Lyme, Conn., were diagnosed with what appeared to be juvenile rheumatoid arthritis. Although young people do get arthritis, children in Lyme were developing joint disease at a rate 100 times greater than normal. Eventually, researchers traced the children's signs and symptoms not to arthritis, but to a bacterial infection transmitted by deer ticks. The infection was named Lyme disease.

Since then, Lyme disease has spread across the United States. Although cases have been reported in almost every state, the disease remains heavily concentrated in three main areas: the Northeast, upper Midwest and northern California. Lyme disease is also found throughout much of Asia and Europe. Even in endemic areas, not all deer ticks are infected with the bacteria that cause Lyme disease, and only a small percentage of people or pets bitten by a deer tick actually become sick.

Still, it's important to take common-sense precautions in areas where Lyme disease is prevalent. Although most people treated with antibiotics in the early stages of the disease recover completely, a few may have recurring or lingering symptoms long after the infection has cleared. Untreated Lyme disease can spread throughout the body, leading to arthritis and other serious health problems.

Lyme disease can affect various parts of the body, producing a wide range of signs and symptoms. Not everyone with the disease will have all of the signs and symptoms, and the signs and symptoms of infection in the United States may be different from those in other countries. But in general, Lyme disease can cause:

• Rash. A small, red bump may appear within a few days to a month at the site of the tick bite — often in your groin, belt area or behind your knee. It may be warm to the touch and mildly tender. Over the next few days, the redness expands, forming a rash that may be as small as a dime or as large as 12 inches across. It often resembles a bull's-eye, with a red ring surrounding a clear area and a red center. The rash, called erythema migrans, is one of the hallmarks of Lyme disease, affecting about 80 percent of infected people. If you're allergic to tick saliva, redness may develop at the site of a tick bite. The redness usually fades within a week. This is not the same as erythema migrans, which tends to expand and get redder over time.
• Flu-like symptoms. A fever, chills, fatigue, body aches and a headache may accompany the rash.
• Migratory joint pain. If the infection remains untreated, you may develop bouts of severe joint pain and swelling several weeks to months after you're infected. Your knees are especially likely to be affected, but the pain can shift from one joint to another.
• Neurological problems. In some cases, inflammation of the membranes surrounding your brain (meningitis), temporary paralysis of one side of your face (Bell's palsy), numbness or weakness in your limbs, and poor muscle movement may occur weeks, months or even years after an untreated infection. Memory loss, difficulty concentrating, and changes in mood or sleep habits also can be symptoms of late-stage Lyme disease.
• Less common signs and symptoms. Some people may experience heart problems — such as an irregular heartbeat — several weeks after infection, but this rarely lasts more than a few days or weeks. Eye inflammation, hepatitis and severe fatigue are possible as well.
• Skin problems. In Europe, people with advanced Lyme disease may develop skin nodules and patches of thinning skin on their hands, elbows or knees.

In the United States, Lyme disease is caused by the bacterium Borrelia burgdorferi, which is carried primarily by deer ticks. The ticks are brown and often no bigger than the head of the pin, which can make them nearly impossible to spot.

Like vampires, ticks thrive on blood, latching onto a host and feeding for four or five days until they're swollen to many times their normal size. During feeding, ticks that carry disease-producing bacteria can transmit the bacteria to a healthy host. Or they may pick up bacteria themselves if the host is infected. In areas where Lyme disease is common, as many as 50 percent of deer ticks may carry Borrelia burgdorferi.

Deer ticks prefer the blood of mice, small birds and deer, but aren't averse to dining on humans, cats, dogs and horses. They live in low bushes and tall grasses of wooded areas, waiting for warmblooded animals to pass by and are most active in the spring, summer and fall.

To contract Lyme disease, you must be bitten by an infected deer tick. The bacteria enter your skin through the bite and eventually make their way into your bloodstream. But because the bacteria aren't transmitted for about 48 hours after the bite, removing the tick as soon as possible can help prevent infection.

Where you live or vacation can affect your chances of getting Lyme disease. So can your profession and the type of outdoor activities you enjoy. The most common risk factors for Lyme disease include:

• Spending time in wooded or grassy areas. In the United States, deer ticks are most prevalent in Massachusetts, Connecticut, Rhode Island, New York, New Jersey, Minnesota, Wisconsin and California. All have heavily wooded areas where deer ticks thrive. In these regions, children who spend a lot of time outdoors are especially at risk. So are people with outdoor occupations and those who live where mice are common. Deer ticks feed on mice, which are a prime reservoir for Lyme disease bacteria.
• Having exposed skin. Ticks attach easily to bare flesh. If you're in an area where ticks are common, protect yourself and your children by wearing long sleeves and long pants. Don't allow your pets to wander in tall weeds and grasses.
• Not removing ticks promptly or properly. Bacteria from a tick bite can enter your bloodstream only if the tick stays attached to your skin for 48 hours or longer. If you remove a tick within two days, your risk of acquiring Lyme disease is low — about 1 percent.

Only a minority of deer tick bites lead to Lyme disease. The longer the tick remains attached to your skin, the greater your risk of contracting the disease. If you know you've been bitten and experience signs and symptoms of Lyme disease — particularly if you live in an area where Lyme disease is prevalent — contact your doctor immediately. Treatment for Lyme disease is most effective if begun early.

It's important to consult your doctor even if signs and symptoms disappear because the absence of symptoms doesn't mean the disease is gone. Left untreated, Lyme disease can spread to the rest of your body from six months to two years after infection — causing arthritis and nervous system problems. Occasionally, ticks can also transmit other illnesses, such as Rocky Mountain spotted fever, Colorado tick fever, ehrlichiosis and tick paralysis.

Lyme disease can be difficult to diagnose. Its variable signs and symptoms mimic other conditions, including viral infections, various joint disorders, muscle pain (fibromyalgia) and chronic fatigue syndrome. What's more, the ticks that transmit Lyme disease can spread other, similar diseases at the same time.

If you don't have the characteristic Lyme disease rash, your doctor will ask detailed questions about your medical history and do a physical exam. Lab tests to identify antibodies to the bacteria may be used to help confirm the diagnosis. These tests are most reliable a few weeks after an infection because it takes your body some time to develop antibodies. Even then, however, the tests aren't entirely foolproof. They include:

• Enzyme-linked immunosorbent assay (ELISA) test. The test used most often to check for Lyme disease, ELISA detects antibodies to B. burgdorferi. But because it can sometimes provide false-positive results, it's not used as the sole basis for diagnosis.
• Western blot test. If the ELISA test is positive, another test — the Western blot — is usually done to confirm the diagnosis. The Western blot detects antibodies to several proteins of B. burgdorferi.
• Polymerase chain reaction (PCR). This test helps detect bacterial DNA in fluid drawn from an infected joint. It's used for people who may have chronic Lyme arthritis. It may also be used to detect persistent infection in the cerebrospinal fluid of people who have nervous system symptoms.

Left untreated, Lyme disease can cause:

• Chronic joint inflammation (Lyme arthritis), particularly of the knee
• Neurological symptoms, such as facial palsy and neuropathy
• Cognitive defects, such as impaired memory
• Sometimes, heart rhythm irregularities

Late-stage symptoms may include:

• Memory loss
• Difficulty concentrating
• Changes in mood or sleep habits

Oral antibiotics — usually doxycycline for adults and children older than 8, or amoxicillin or cefuroxime axetil for adults and younger children — are the standard treatment for early-stage Lyme disease. These drugs often clear the infection and prevent complications. A 14- to 21-day course of antibiotics is usually recommended, but some studies suggest that courses lasting 10 to 14 days are equally effective. In some cases, longer treatment has been linked to serious complications.

If the disease has progressed, your doctor may recommend treatment with an intravenous antibiotic for 14 to 28 days. This is usually effective, although it may take some time to recover. Intravenous antibiotics can cause various side effects, including a lower white blood cell count, gallstones and mild to severe diarrhea.

The Food and Drug Administration (FDA) warns consumers and health care providers to avoid bismacine, an injectable compound prescribed by some alternative medicine practitioners to treat Lyme disease. Bismacine, also known as chromacine, contains high levels of the metal bismuth. Although bismuth is safely used in some oral medications for stomach ulcers, it's not approved for use in injectable form or as a treatment for Lyme disease. Bismacine can cause bismuth poisoning, which may lead to heart and kidney failure.

In March 2005, one person was hospitalized after receiving a bismacine treatment, according to the FDA. In April 2006, another person died as a result of treatment with bismacine.

You can decrease your risk of contracting Lyme disease with some simple precautions:

• Wear long pants and sleeves. When walking in wooded or grassy areas, wear shoes, long pants tucked into your socks, a long-sleeved shirt, a hat and gloves. Try to stick to trails and avoid walking through low bushes and long grass. Keep your dog on a leash.
• Use insect repellents. Apply an insect repellent with a 10 percent to 30 percent concentration of DEET to your skin and clothing. Choose the concentration based on the hours of protection you need — a 10 percent concentration is effective for about two hours, while higher concentrations last longer. Keep in mind that chemical repellents can be toxic, and use only the amount needed for the time you'll be outdoors. Don't use DEET on the hands of young children or on infants younger than age 2 months. According to the Centers for Disease Control and Prevention, oil of lemon eucalyptus, a more natural product, offers the same protection as DEET when used in similar concentrations. Other natural repellents, such as citronella and oil of geranium, also offer some protection.
• Do your best to tick-proof your yard. Clear brush and leaves where ticks live. Keep woodpiles in sunny areas.
• Check yourself, your children and your pets for ticks. Be especially vigilant after spending time in wooded or grassy areas. Deer ticks are often no bigger than the head of a pin, so you may not discover them unless you search carefully. It's helpful to shower as soon as you come indoors. Ticks often remain on your skin for hours before attaching themselves.
• Don't assume you're immune. Even if you've had Lyme disease before, you can get it again.
• Remove a tick with tweezers. Gently grasp the tick near its head or mouth. Don't squeeze or crush the tick, but pull carefully and steadily. Once you've removed the entire tick, apply antiseptic to the bite area.

Lyme disease vaccine
In 2002, distribution of a Lyme disease vaccine (Lymerix) was halted due to concerns about the drug's safety and effectiveness. Research on other vaccines against B. burgdorferi continues.