Tick-Borne Disease Risk Peaks in Spring and Summer

Harvard Health

Lyme disease is by far the most common tick-borne disease in the United States. Between 20,000 and 30,000 cases have been reported in most of the past several years, and health officials suspect many more go unreported. The incidence is highest in New England, the Mid-Atlantic states, and Wisconsin.

Deer ticks are responsible for the vast majority of Lyme disease cases, although a related tick, Ixodes pacificus, found in the western United States, also can transmit the Borrelia burgdorferi bacteria that cause Lyme disease.

Ticks are a source of human illness because they're able to harbor a disease-causing organism acquired at an earlier stage, which they transmit in their saliva as they enjoy a blood meal during their next one. Deer ticks, for example, pick up the B. burgdorferi when they feed on mice as larvae or nymphs. Neither the ticks nor the mice are the least bit fazed by the bacterial infection. But if an infected tick then feeds on a person, and enough B. burgdorferi gets into that person's skin, he or she may come down with Lyme disease.

DEER, DOG, AND LONE STAR

Deer ticks are called by that name because during their adult phase they favor deer. They're also known descriptively as black-legged ticks, and the scientific binomial is Ixodes scapularis.

Deer ticks shouldn't be confused with dog ticks (which are sometimes called wood ticks: Dermacentor variabilis). The two species are prevalent in the same parts of the United States, although dog ticks are a little more widespread. One way you can tell the two species apart is by their size: Dog ticks are much larger than deer ticks. The size difference is especially apparent during the warmer months. Both the adult dog ticks and deer tick nymphs will be active, and adult dog ticks are more than 10 times larger than tiny deer tick nymphs, which are about the size of a poppy seed.

Coloring and markings are also clues. The female deer tick has a two-tone appearance because of a reddish body and a dark area on its back near the head. The male is black or dark brown. The dog tick has distinctive whitish markings on its back.

The deer ticks in this country transmit pathogens that cause two other diseases besides Lyme: babesiosis, an illness that resembles malaria, and human granulocytic anaplasmosis (often shortened to just anaplasmosis), which causes flulike symptoms. Some studies have shown that people can get one of these other diseases and Lyme disease simultaneously.

Deer ticks also harbor and spread viruses, but in the United States, viral disease hasn't been a problem, although in 2009 there was a case report of a 62-year-old New York State resident dying from a deer tick virus infection.

Dog ticks aren't a cause of Lyme disease. However, they can infect people with the Rickettsia rickettsii bacterium that causes Rocky Mountain spotted fever, which isn't as common as Lyme disease, but is lethal in a small percentage of cases. The name is now a bit misleading: Most of the 1,000 or so cases of Rocky Mountain spotted fever that occur each year affect people living in a swath of south-central states that includes Oklahoma, Arkansas, Tennessee, and North and South Carolina. Dog ticks elsewhere are far less likely to be infected with R. rickettsii.

Another type of tick, the lone star, is spreading into the Northeast from the Southeast. It gets its name because of the distinctive white spot on its back. Lone star ticks don't carry B. burgdorferi but their bites can result in diseases with similar symptoms.

LYME SYMPTOMS AND TREATMENT

The first time many of us heard about a bull's-eye rash was in the mid-1970s, when Lyme disease was first recognized. The red rash with a clear center was supposed to be the calling card of the new disease. That turned out to be misleading. Erythema migrans, the medical term for the rash, may take on the bull's-eye appearance, but not right away; early on, it's usually uniformly red or, occasionally, blotchy. The telltale feature is that it gets larger. If you mark the border in pen and it doesn't grow outside the pen mark in 24 hours, then it's probably not erythema migrans.

Common locations include hard-to-see places like the groin and the armpits. The rash may not appear until weeks after the tick has detached and is long gone, and people with Lyme disease often miss the tick bite that initiated the disease. Early on, Lyme disease also makes people feel crummy, like they have the flu.

If the infection spreads beyond the site of the bite, the B. burgdorferi bacteria can cause arthritis and get into nervous tissue, resulting in a number of neurological symptoms, including numbness and pain in the arms and legs, facial paralysis on one side, a stiff neck, and severe headaches. Very rarely, the heart is affected.

Lyme disease is diagnosed based on symptoms and a history of possible exposure to infectious ticks. Lab tests for antibodies to the infection can help clinch the diagnosis but need to be interpreted carefully. If blood is tested during the early part of the infection, when the rash is the main symptom, then the test is likely to be negative for antibodies. A second follow-up test about a month later should be ordered. But if antibiotics are started early, there's a good chance that the second test may be negative.

Antibiotics effectively treat most cases of Lyme disease. If the infection is caught early, an oral course is sufficient and should limit the symptoms to the rash and the flulike symptoms. Arthritis from Lyme disease is also treated with oral antibiotics. If neurological symptoms occur, the intravenous route may be necessary.

Generally speaking, doctors won't give someone antibiotics for just a tick bite, but current guidelines say a single dose of the antibiotic doxycycline may be appropriate if the tick has been attached for 36 hours and came from an area with a lot of Lyme disease.

THE BIG CONTROVERSY

Some community doctors and Lyme disease patients have argued -- often passionately -- that B. burgdorferi can evade courses of antibiotics and become a chronic infection that needs long-term antibiotic treatment, even though conventional antibody tests are negative. Chronic Lyme disease has been blamed for causing pain, fatigue, muscle aches, cognitive shortcomings, and a host of other problems.

But many -- some might say most -- Lyme disease experts don't believe active infection persists after antibiotic treatment and once blood tests are negative for antibodies. They've been critical of what they see as unreliable tests for infection and unwarranted, possibly harmful, long-term antibiotic therapy.

Post-Lyme disease syndrome has been proposed as an alternative explanation -- and label -- for some of these cases of lingering illness. The notion is that some people are sick because their immune system has become dysfunctional or they've developed some other abnormality. Others may be ill for reasons unrelated to Lyme.

In most medical contexts, specialists would politely discuss these issues. But in Lyme disease circles, the debate has been emotional, and acrimonious. Charges of quackery and of conspiracies with insurance companies have flown back and forth. Connecticut's attorney general, Richard Blumenthal, got involved by opening an antitrust investigation into the Infectious Diseases Society of America, which recommended against long-term antibiotics in its 2006 guidelines. Eventually, the society entered into an agreement with Blumenthal that included a voluntary review of the guidelines.

NOW IT THE TIME TO BE WARY

The spring and summer months are when you need to be most wary of deer ticks and the potential for coming down with Lyme disease. The nymphs are most active in May, June, and July, months when people get outside. Over 95 percent of all Lyme disease cases start with a bite by a nymph, not an adult tick, partly because the nymphs are so tiny that they're difficult to spot. Adult deer ticks are also a source of Lyme disease, but they're active during the fall and on warm winter days.

Deer ticks would be even more of a menace if it weren't for the fact that they're slow eaters: it takes them several days to get a full blood meal and for their bacteria-laden saliva to infect someone. In fact, the chances of a tick transmitting B. burgdorferi during the first 24 hours of its meal is almost zero and slowly climbs over a four-day period.

If you remove a tick early, even if it has put its long, barbed mouthparts into you, your chances of getting Lyme disease are low. Moreover, even in areas where Lyme disease is common, usually only a minority of the ticks are carrying the bacteria that cause the disease.

TIPS TO WARD OFF TICKS

The Connecticut Agricultural Experiment Station published an excellent handbook about tick management several years ago. We've posted a link to it (the full text is available online) on our Web site: www.health.edu/healthextra. Meanwhile, here are eight tips for protecting yourself from ticks, culled mainly from the handbook:

1. Wear light-colored clothing.

Light colors make ticks easier to spot, especially the tiny deer tick nymphs.

2. Tuck your pants inside your socks.

It's not a flattering look, and the Connecticut handbook says it's unclear just how effective it is, but tucking your pants into your socks does create a physical barrier against ticks.

3. Wear insect repellent.

Most of the chemicals that repel mosquitoes are somewhat effective against ticks, although it may take a heavier concentration of DEET -- between 30 percent and 40 percent -- to really keep the them away. Permethrin is a stronger chemical that kills ticks as well as repels them. Products containing permethrin should be sprayed on clothes, not on the skin. Picaridin repels mosquitoes and other insects but not ticks.

4. Stay in the middle of the path (or fairway).

Ticks can't fly or jump, so they can only get on you if you come into contact with the kind of environment they live in: moist, often shady, wooded areas, with leaves, low-lying plants, and shrubs. There's a joke that duffers are more likely to get Lyme disease than good golfers because they're in the rough more often.

5. Inspect yourself and your children, especially the legs and groin.

Most ticks probably get picked up on the lower legs and then climb upward in search of dinner. The chances of contracting Lyme disease are minimized if a tick is removed soon after it's attached, and there's no risk if it's still crawling around. The shower is a good place to conduct a tick check. Feel for any new bumps on soaped-up skin.

6. Remove gently.

Use tweezers to grab the tick as close to the skin as possible. You can also use a needle to very gently pry it off. If the mouthparts break off and are left in the skin, they don't usually cause any harm.

7. Put your clothes in the dryer.

Deer ticks and lone star ticks can survive a hot-water wash, but an hour in a dryer will kill them.

8. Think sunny.

Ticks don't do well in dry, open areas. Lawn furniture and playground equipment should be set back from the edge of wooded, shady areas. If you're picnicking, pick a patch of well-tended lawn or some open ground -- and put on sunscreen.

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