Malaria is not the only insect-borne disease now afflicting Americans.
Lyme disease, named after the city in Connecticut where it was first identified, comes from the bite of a tick infected with a spirochetal bacterium.
Two species of tick, Ixodes scapularis and I. pacificus, are the primary villains. I. scapularis lives in the East and Midwest; I. pacificus, as its name suggests, is found along the coast of California. But it may be that being worried sick about Lyme disease is more common than being sick with the bacterium that causes it.
You need three things in the environment for Lyme disease to occur: the bacterium, the tick, and mammals, usually deer and mice. Without these three elements, you can’t have Lyme disease. Unfortunately, there are many parts of the country in which all three elements thrive together.
Ixodes ticks have a long and complicated life cycle that takes two years to complete. The adult ticks live on large animals like deer, where they feed on blood and then mate. This happens in the fall and early spring. By summer, the female ticks drop off the animal and lay eggs on the ground, where they hatch into larvae. These larvae attach themselves to birds and small mammals to get their blood meals.
The following spring, they molt into nymphs. The nymph stage also feeds on small mammals and birds and then in the fall molts again, becoming an adult. It is at the nymph and larval stages that the tick becomes infected with Borrelia burgdorferi, usually by feeding on the white-footed mouse, and the bacterium continues to live in the insect after it becomes an adult. Then the adults feed on deer, starting the life cycle over again. When the tick bites a human, it inserts the bacterium into the person’s bloodstream, where it causes Lyme disease.
These insects are tiny, hardly bigger than a pinhead in their larval and nymph stages, and only slightly larger as adults. They’ll attach themselves anywhere, but they seem to prefer hairy and hidden areas, armpits, groin, scalp. The ticks, and in humans, it is usually the nymph stage that does the biting, are so small that they often go unnoticed, and remain unnoticed during the two days of feeding usually required to transmit infection.
The adults are easier to see, and therefore more likely to be removed before they cause infection. (Also, the adults live in cooler weather, when people are less likely to be outdoors where they can encounter them.) The larval stage, while it may be infected, usually doesn’t carry the infection at the time it feeds, so it doesn’t play a significant role in transmission.
Ticks don’t jump, fly, or otherwise move through the air. And they don’t live in trees. They crawl around in grass and shrubs, and you have to rub up against them to get them attached to you. If a tick makes it as far as your scalp, it crawled there from some other part of your body (unless you’ve had your head lying on the ground, which is of course possible).
After they bite (and they do not insert their whole bodies, only their mouth parts) they spend about two days feeding before their meal is done. Mosquitoes, flies, and fleas don’t carry Lyme disease. You can’t catch it from another person no matter how close your contact. You can’t get it from handling live or dead infected birds. You can’t get Lyme disease directly from deer or domestic animals, you can’t get it from the air, water, or food you consume, you can’t get it from having sex, and although in theory you could get it from contact with blood or a blood transfusion, there’s never been a documented case of that happening.
While the number of cases reported has gone up and down in the past few years, there is little question that the overall trend is upward. The geographic area affected expanded in the early years but has since stabilized. In 1999, three states, Connecticut, New York, and Pennsylvania, accounted for 10,398 of 16,273 cases reported. There have been cases reported in all 48 contiguous states, but most of the cases are concentrated in the mid-Atlantic and north central regions in the East, and in a few counties of northern California.
The earliest sign of Lyme disease is a circular “bull’s-eye” rash, red around the edges and white at the center, with the circumference growing over time. This is called “erythema migrans.” There are also often nonspecific symptoms, headaches, muscle and joint pains, fatigue, malaise. The rash usually appears about 7 to 14 days after the infection, but it can appear as soon as three days or as many as 30 days after.
As the disease progresses, the rash spreads, and disseminated infection may appear as a disease of the nervous system, the musculoskeletal system, or the heart. Neurological manifestations can include dysfunctions of the cranial nerves (including facial nerves) and spinal cord nerves. You can be infected without any symptoms, a blood test can determine this by detecting the antigens to B. burgdorferi. Having produced antigens to B. burgdorferi does not inevitably confer immunity to repeated infection.
Lyme disease accounts for 95 percent of all vector-borne disease (that is, requiring an animal carrier before you can be infected) in the United States. There have been more than 128,000 cases since reporting began in 1982, but the true figure may be larger because of underreporting.
The best way to avoid Lyme disease, obviously, is to avoid areas where there are ticks, especially in the spring and summer when the nymphs are feeding. But if your backyard is in, say, Connecticut or along the Pacific coast north of San Francisco, it may not be practical to follow this advice.
Ticks like a moist, shaded environment, particularly overgrown grassy areas, leaf litter, and low-lying vegetation. So it’s helpful to clean up these areas or just stay away from them. Wearing long-sleeved shirts and long pants tucked into socks or boot tops is also a good idea. And the application of insect repellents that contain DEET (n,n-diethyl-m toluamide) to clothes and skin also helps. A concentration of 35 percent DEET is effective; higher concentrations than that provide no additional protection. Permethrin, which kills ticks on contact, can be applied to clothes.
If a tick attaches itself to you, you have about 36 hours to get rid of it before it can cause Lyme infection, so checking for ticks and removing them when you find them is important. Before they bite, and they can be on you for hours before they settle down for a meal, they can simply be wiped or washed off. After they’ve attached themselves to the skin, fine-tipped tweezers are the best way to pull them off. Petroleum jelly, hot matches, nail polish, and other home remedies don’t work. When you pull the tick off, it doesn’t matter if the mouth parts remain in the skin, the bacteria are in the insect’s stomach. The area should be cleansed with antiseptic when you’re done. You only need medical treatment if the early signs of Lyme disease appear.
There are two vaccines for Lyme disease. One called LYMErix is manufactured by SmithKline Beecham Pharmaceuticals and can be used for people over the age of 15. The other is called ImuLyme, made by Pasteur Merieux Connaught, but as of early 2002 was not licensed for use in the United States. The Advisory Commission on Immunization Practices of the CDC recommends that people between 15 and 70 years old who live, work, or spend leisure time in areas of high or moderate risk and engage in activities that result in prolonged exposure to tick-infested habitats should get the vaccination. It can be considered for people whose exposure is less frequent, but it is not recommended for people who have only minimal exposure to tick-infested habitats.
Travelers to high-risk areas should consider having the vaccination, but should remember that they cannot achieve full protection until three doses have been given. Since doses must be given at 0, 1 month, and 12 months, it is a full year before the protection reaches its maximum.
Also, vaccine administration (by intramuscular injection) should be timed so that the second and third doses are administered several weeks before the beginning of the B. burgdorferi transmission season, which usually begins in April. There aren’t enough data to know whether boosters are necessary after two years. Considering everything, personal protection may be a better or at least equally effective approach for travelers.
Pregnant women shouldn’t get the vaccination because its safety during pregnancy has not been established, and because acute Lyme disease during pregnancy responds well to antibiotic therapy without harming the fetus.
There are no data on the safety of the vaccine for people with impaired immune systems, those with musculoskeletal illnesses, or those with chronic joint or neurological illness, so they should not be vaccinated, nor should people who have treatment-resistant Lyme arthritis or second or third-degree atrioventricular block, a form of heart disease.
If you get Lyme disease, the latest research indicates that it can easily be stopped with a single dose of the antibiotic doxycycline. A study conducted in Westchester County, New York, divided 482 people who had found deer ticks on their bodies into two groups. One group got a single dose of doxycycline, administered in two pills. The other group got two placebo pills. The results showed that the single dose worked, only one of the people who got the antibiotic, 0.4 percent of the total, came down with Lyme disease. In the placebo group, 3 percent came down with the illness. This suggests two things: first, Lyme disease is hard to catch; and second, it’s not hard to cure.
The antibiotic, however, can cause problems in itself, nausea, vomiting, and abdominal pain, and among those in the study who took it, there would have been little chance of getting Lyme disease even if they hadn’t taken it. The latest recommendation is to watch the site of the bite to see if a rash develops. If it does, a few weeks of antibiotic treatment will cure the illness. Those who have symptoms after this are probably not suffering from Lyme disease, but from some other ailment.
In fact, most people who are infected get better without any treatment at all. A small percentage of infected people develop more serious symptoms, arthritis or heart disease, but even the majority of these people get better without treatment. Worrying about Lyme disease may cause more problems than Lyme disease itself.
Dr. Leonard H. Sigal, a Lyme disease expert at the University of Medicine and Dentistry of New Jersey–Robert Wood Johnson Medical Center in New Brunswick, was quoted in the New York Times: “Lyme disease, although a problem, is not nearly as big a problem as most people think. The bigger epidemic is Lyme anxiety.”