Infelction: Lyme Disease
Infelction: Lyme Disease
Lyme disease is an infectious disease caused by a spirochete (spiral-shaped bacterium) transmitted to humans by the bite of an infected deer tick. The alternate name of Lyme disease—borreliosis—comes from the scientific name of the bacterium, Borrelia burgdorferi. Lyme disease can be classified as an infectious arthritis because the body's immune response to the bacterium produces inflammation and arthritis-like joint or muscle pain in some people.
Lyme disease is considered a zoonosis, or disease transmitted by animals to humans, as well as an emerging infectious disease. Household pets (cats and dogs) that are allowed outdoors can be infected with Lyme disease as well as humans. Typical symptoms of Lyme disease in animals include joint soreness, limping or lameness, fever, and loss of appetite.
An infectious disease, Lyme disease is caused by a spiral-shaped bacterium that lives inside deer ticks. The tick transmits the disease from one animal to another or from animals to humans when it feeds on their blood. The symptoms of the disease vary from person to person. Not everyone who gets Lyme disease has all the symptoms or has them with equal severity.
The first stage of Lyme disease is often (though not always) marked by a red rash known as erythema chronicum migrans, or EM, at the site of the tick bite. The rash may have a circular or bull's-eye appearance. It occurs in about 80 percent of patients within three to thirty days after the bite. The rash expands over the next few days to cover as much as 12 inches (30 centimeters) of skin. Patients may also have flulike symptoms, including fatigue, chills, low-grade fever, headache, muscle and joint aches, and swollen lymph nodes. In some cases, these flu-like symptoms may be the only indication of Lyme infection.
If the infection is not treated, patients may develop a second stage of symptoms that can include heart palpitations, fatigue, headaches, temporary paralysis of facial muscles, meningitis, or dizziness.
Some patients experience a third stage of the disease, marked by arthritis-like pain in the joints and muscles, numbness in the arms and legs, loss of memory, and other neurological symptoms.
The Centers for Disease Control and Prevention (CDC) reported 23,305 cases of Lyme disease in the United States in 2005. Most occurred in the coastal Northeast, the Mid-Atlantic States, Wisconsin and Minnesota, and northern California. Most cases of Lyme disease occur in the spring and summer months when ticks are most active and people are spending more time outside. In both the United States and Europe, the age groups most likely to be affected are children between the ages of five and nine years, and adults between fifty and fifty-nine. Among children, boys are
The Long History of Lyme Disease
Lyme disease is named for Old Lyme, the town in Connecticut where an outbreak of the disease among children in the early 1970s was described by a physician at nearby Yale University. The infectious form of arthritis, however, had been described as far back as the early 1900s in Europe. In 1909, Swedish doctor Arvid Afzelius described a patient with a rash now known as erythema chronicum migrans—or simply erythema migrans (EM)—an early symptom of the disease. By 1934 other European doctors had noted that patients with the strange circular rash eventually developed arthritis-like joint pain and in some cases, psychiatric or neurological symptoms. They had also traced the rash to tick bites.
After World War II, European doctors found that newly developed antibiotics were quite effective in treating the tick-borne disease. The first known case of EM in the United States was reported in 1970 by a doctor in Wisconsin who was treating a patient bitten by a tick while hunting. The first cluster of cases of Lyme disease in the United States occurred in 1976 at a U.S. naval base in Connecticut. The following year saw cases involving the school children of Old Lyme. At that time, the disease was called Lyme arthritis. In 1982 Willy Burgdorfer, a researcher with the Rocky Mountain Laboratories of the National Institutes of Health, identified the cause of Lyme disease while gathering black-legged ticks in Montana. The organism was named Borrelia burgdorferi in his honor. Researchers have shown two other Borrelia species cause the European form of Lyme disease.
more likely to be infected than girls, but in the older age group, women are slightly more likely than men to get Lyme disease. In 1998, Caucasians accounted for 76 percent of reported cases of Lyme disease in the United States, but it is not known whether this statistic indicates greater susceptibility to the disease or simply regional differences in reporting.
The cause of Lyme disease is a spirochete carried from one animal or human host to another by several varieties of ticks found in the United States. These ticks have a two-year life cycle. They are born in the summer as larvae and feed only once, on the blood of field mice. The next spring, the larva becomes a nymph and feeds again on a mouse's blood. In the fall, the nymph becomes an adult tick and feeds on the blood of a white-tailed deer. If the tick has picked up the spirochete from the mice or the deer, it can transmit the disease to a human at this point.
It takes one to three days for the tick to transmit B. burgdorferi to a human because it takes time for the bacterium to multiply inside the tick after it has bitten a person. Once feeding begins, the bacteria inside the tick multiply rapidly and move into the salivary glands of the tick after one to two days or so. The tick then injects the bacteria into the human as it continues its feeding. This time delay is one reason why prompt removal of a tick is usually effective in preventing Lyme disease and most other tick-borne infections.
The diagnosis of Lyme disease is complicated by several factors. The first is that only 20 percent of patients are aware that they have been bitten by a tick. If they do not develop the characteristic EM rash, the diagnosis may be delayed. Second, the ticks that carry Lyme disease also often carry other diseases like ehrlichiosis or babesiosis, so that a person may have another tick-borne infection alongside or instead of Lyme disease. Third, most of the symptoms of Lyme disease can be caused by a variety of other disorders, including rheumatoid arthritis, complications of gonorrhea, lupus, or gout.
The CDC recommends as of 2007 that doctors look for three factors when evaluating a patient who might have Lyme disease:
- A history of possible exposure to ticks in parts of the United States known to have a higher than average rate of Lyme disease
- Physical symptoms that include EM
- A blood test that shows the patient has antibodies to B. burgdorferi
Even so, blood tests are not 100 percent accurate, particularly if they are given before the patient's body has had time to develop antibodies to the spirochete. In most parts of the United States, an initial blood test for antibodies is followed up by a second test known as a Western blot test to confirm the diagnosis.
Early-stage Lyme disease can be effectively treated with a fourteen- to twenty-one-day course of antibiotics taken by mouth. These drugs usually clear the infection and reduce the risk of later complications. Second- or third-stage Lyme disease is treated with either a thirty-day course of an oral antibiotic or fourteen to twenty-eight days of an intravenous antibiotic.
The prognosis of Lyme disease is difficult to estimate because of the fact that EM is sometimes misdiagnosed. Further, many patients do not return for follow-up visits, which complicates the doctor's ability to measure the effectiveness of treatment or record the length of time that the patient had symptoms. In general, children who are treated early with antibiotics have an excellent prognosis for complete recovery. Adults are more likely to develop chronic muscle and joint pain or fatigue, but generally recover given time and appropriate treatment. Although there have been a few fatal cases of Lyme disease in humans as of 2008, the overall mortality rate is extremely low.
A vaccine effective against Lyme disease was released in 1998 but was taken off the market because of the possible side effects reported by some patients and because it was not widely used. Although research into a better vaccine is ongoing, there was no vaccine available against the disease as of mid-2008. Preventive measures against Lyme disease are important because of the lack of an effective vaccine. The CDC recommends the following precautions:
- Stay away from wooded, brushy, and grassy areas, especially in May, June, and July. These are the months when ticks are most likely to feed on humans and pets.
- Wear light-colored clothing (which allows the ticks to be seen more easily); shoes that cover the entire foot; long pants tucked into socks or shoes; and long-sleeved shirts tucked into pants. Also wear a hat for additional protection.
- Use insect repellent containing a chemical called DEET on clothes and exposed skin other than the face. Another repellent that can be used on clothing is permethrin, which kills ticks on contact.
- When hiking in the woods, walk in the center of the trail or path; avoid brush and tall grasses.
- Remove clothing after being outside; wash it in hot water and dry it in a dryer on a high setting.
- Check the body for ticks after being outside, particularly the hair, the groin area, and the armpits.
- Check pets allowed outdoors for ticks in their fur, and give them tick-repellent collars. There is a vaccine to protect dogs against Lyme disease; there is, however, no vaccine for cats as of 2008. Cats appear to be much less likely to get the disease than dogs, which can develop fatal kidney problems from Lyme disease.
- Remove a tick properly if one is found on the body. Grasp the tick near its head or mouth, as it is critical to remove the head intact. Do not crush the tick but pull it backward from the skin slowly and carefully. Take the tick to a doctor or local public health department so that it can be tested to see if it is a Lyme disease-related tick.
Lyme disease is likely to become more common in North America in the years ahead because of the rising number of deer, mice, and other small rodents that can be infected by B. burgdorferi, and the increased amount of contact between humans and these animals in wooded areas. This increased contact is partly due to the growing popularity of woodland hiking and fishing and partly to the building of new houses in tick-infested areas. The CDC reports that Lyme disease was one of the fastest-growing infectious diseases in the United States as of 2008 and that it has spread from the regions where it was first noticed to forty-nine of the fifty states. Researchers are working on developing a new vaccine against Lyme disease. In addition, other scientists are trying to learn more
about the bacterium that causes the disease in order to develop better ways to diagnose and treat it.
SEE ALSO Lupus; Rheumatoid arthritis
WORDS TO KNOW
Babesiosis: A malaria-like disease that can be transmitted by ticks.
Ehrlichiosis: A tick-borne disease found primarily in dogs that can also be transmitted to humans.
Emerging infectious disease (EID): A disease that has become more widespread around the world in the last twenty years and is expected to become more common in the future.
Endemic: A term applied to a disease that maintains itself in a particular area without reinforcement from outside sources of infection.
Erythema chronicum migrans (EM): The medical name for the distinctive rash that is often seen in early-stage Lyme disease.
Larva: The immature form of a deer tick.
Meningitis: Inflammation of the membranes covering the brain and spinal cord.
Nymph: The second stage in the life cycle of the deer tick.
Spirochete: A spiral-shaped bacterium. Lyme disease is caused by a spirochete.
Tick: A small bloodsucking parasitic insect that carries Lyme disease and several other diseases.
Zoonosis: A disease that animals can transmit to humans.
Food and Drug Administration (FDA) Consumer Update. “Beware of Ticks … and Lyme Disease,” June 27, 2007. Available online at http://www.fda.gov/consumer/updates/lymedisease062707.html (accessed May 24, 2008).
American College of Physicians (ACP). “Lyme Disease: A Patient's Guide.” Available online at http://www.acponline.org/clinical_information/resources/lyme_disease/patient/ (updated 2008; accessed May 23, 2008).
American Lyme Disease Foundation. “Lyme Disease.” Available online at http://www.aldf.com/lyme.shtml (updated 2006; accessed May 23, 2008).
Centers for Disease Control and Prevention (CDC). “National Lyme Disease Risk Map.” Available online at http://www.cdc.gov/ncidod/dvbid/lyme/riskmap.htm (updated 2004; accessed May 23, 2008).
Patient Education Institute, National Library of Medicine. “Lyme Disease.” Available online at http://www.nlm.nih.gov/medlineplus/tutorials/lymedisease/htm/lesson.htm (accessed May 23, 2008). This is an interactive tutorial with voiceover about Lyme disease.