Recognizing and avoiding tick-borne illness

Most tick bites won't make you sick, but the ones that do can be serious.

June is here and the bugs are out — in yards and gardens, at the beach, and along hiking trails and pathways. Most are just an annoyance, but some are vectors, or transmitters, of disease.

In the United States, the chief culprits are ticks — in particular, the deer tick (also called the black-legged tick), which can carry and transmit the bacterium responsible for Lyme disease. Considered somewhat rare in the mid-1980s, Lyme disease is now the most common vector-borne illness in the United States. About 20,000 cases are reported annually to the CDC, and the agency says that's only 10% of the total.

We consulted tick expert Dr. Jonathan Edlow of Harvard Medical School and Boston's Beth Israel Deaconess Medical Center, whose book Bull's Eye: Unraveling the Medical Mystery of Lyme Disease, outlines the history of this emerging infectious disease. According to Dr. Edlow, there are several reasons for the rising incidence of Lyme disease. Its geographical range has expanded, mostly because of the growing deer population, which harbors the ticks. Also, land once cleared for farming has become reforested, attracting more deer (and other tick hosts) as well as suburban development. As a result, says Dr. Edlow, "people's day-to-day activities — their hobbies, their work, and where they live — put them in closer contact with wildlife than they were in the 1950s." Finally, both patients and clinicians recognize the disease more readily than ever before.

Lyme disease is the predominant tick-borne illness in the United States, but it's not the only one. Ticks can spread other bacterial and viral diseases, including babesiosis, anaplasmosis, ehrlichiosis, tularemia, Rocky Mountain spotted fever, relapsing fever, Colorado tick fever, and southern tick-associated rash illness (STARI). Tick paralysis, another tick-borne disease, is caused not by an infectious organism but by a toxin that the tick itself produces. Most tick bites won't give you a disease, but some can, and there is no vaccine to protect you from the vast majority of these diseases. (There is a vaccine for European tick-borne encephalitis). It's almost impossible to avoid ticks completely, especially if you spend time outdoors. But you can take steps to lower your risk of getting bitten or, if you're bitten, of becoming ill.

What makes a tick tick?

A deer tick's life cycle typically spans two years and involves four stages of development: egg, larva, nymph, and adult. At the larval stage, the tick is barely bigger than a pinpoint. A nymph tick is about the size of a poppy seed. An adult tick looks like a tiny spider and is not quite one-eighth of an inch long (other tick species may be slightly larger). An adult tick engorged with blood may be the size of a small marble. To mature from one stage to the next, the tick needs a blood meal. Larvae and nymphs feed on small vertebrates such as birds and rodents (in particular, the white-footed mouse). Adult ticks attach to larger hosts — chiefly deer — where they mate and feed before the female drops off to lay eggs. Over a lifetime, a tick may feed on a wide variety of animals, potentially putting it in contact with several infectious organisms.

If ticks weren't bloodsucking, disease-spreading parasites, we might be more inclined to admire how well engineered they are. They have receptors on their front legs that detect small vibrations and the breath of passing animals and people. A tick that is "questing" — seeking a blood meal — will perch on tall grass or low bushes and wave its front legs, which are equipped with small barbs for latching on to fur, feathers, or skin. Once it gets on its host, the tick may crawl around for several hours before attaching.

To feed, the tick inserts a tube-like mouthpart called a hypostome into the skin (see the illustration below) and secretes a salivary cement to hold the mouthpart in place. Backward-pointing barbs on the hypostome help secure the connection. Tick saliva also contains substances that facilitate feeding (and disease transmission), including anticoagulants, anti-inflammatory and immunosuppressive agents, and vasodilators. During the blood meal, pathogenic (disease-causing) organisms in the tick's gut migrate to the salivary gland and can be transmitted to the host.

It's not clear how long an infected tick must be attached before it transmits a disease (a crawling tick doesn't transmit anything). For Lyme disease, it probably takes one to three days. "It's a spectrum, but the faster you get it off, the less likely you are to get sick from it," says Dr. Edlow.

Signs, symptoms, and treatment

Tick-borne diseases occur throughout the United States, chiefly in late spring and summer, when ticks are most active and most likely to come in contact with humans. Symptoms vary but usually include fever, chills, muscle aches and pains, headache, and sometimes nausea or a rash. Lyme disease, caused by the bacterium Borrelia burgdorferi, is usually heralded by erythema migrans (EM), an expanding area of redness surrounding the tick bite. Rocky Mountain spotted fever and tick-borne relapsing fever start with sudden high fever and chills.

Most tick-borne illness is caused by bacteria, so it can be treated with antibiotics. But it's important to diagnose the problem early, to avoid complications. For example, a delay in diagnosing Lyme disease can result in cardiac symptoms, neurological problems, and arthritis. Luckily, most people develop EM, the telltale early sign, although you can miss it if it appears on the scalp or another hard-to-see area. Some EM clears centrally to form a "bull's eye," which is regarded as a diagnostic sign of Lyme disease and a reason to start antibiotic therapy. But the most common pattern is "a uniform redness without the bull's eye," says Dr. Edlow.

The most lethal tick-borne disease in the United States is Rocky Mountain spotted fever, caused by the Rickettsia rickettsii bacterium. Despite its name, the disease is found mostly in the southeastern United States; 600 to 1,000 cases are reported each year, but health experts think many more cases are not reported. Cells in the lining and walls of blood vessels are infected and organs and systems throughout the body may suffer. Even with prompt treatment, 3% to 5% of cases result in death; without treatment, mortality may be as high as 25%. Other emerging tick-borne diseases in humans include babesiosis, a malaria-like parasitic infection that was once largely a veterinary problem, and anaplasmosis and ehrlichiosis, which have similar symptoms but are caused by different organisms. Tick-borne encephalitis, a viral disease, is found throughout Europe and Asia but is still rare in the United States.

Some ticks transmit more than one disease, sometimes from the same bite. The deer tick can transmit babesiosis and anaplasmosis as well as Lyme disease. Lone star ticks are linked to human ehrlichiosis and STARI, a Lyme-like disease. The American dog tick carries Rocky Mountain spotted fever and tularemia; it can also cause tick paralysis.

How to protect yourself

If you may have been exposed to ticks and you develop flulike symptoms or a rash, see your clinician — even if the symptoms go away on their own. Tick-borne infection usually causes no lasting harm if it's recognized and treated early. Of course, it's better to avoid getting infected in the first place. To that end, here are some measures you can take:

Protect yourself. Whenever possible, avoid tick habitats — wooded, bushy, or grassy areas, including those near beaches and sand dunes. If you'll be outdoors in tick-infested areas, wear light-colored clothing (to make ticks easier to spot) with long sleeves and long pants tucked into your socks (to keep ticks away from your skin). Use a DEET-containing insect repellent on exposed skin (but not under clothes). Don't spray the DEET directly on your face; spray it into your hands and then apply it to the face. Consult a pediatrician before using it on young children. Wash your hands afterward to avoid getting it into your eyes and mouth. Use permethrin-containing products on clothing, footwear, and camping gear (including cots, nets, and tents). Spray items for 30 to 45 seconds and allow them to dry for two to four hours before wearing or using them. Permethrin should not be applied to the skin.

Do a tick drag. This is a way to find out whether there are ticks in your yard. Attach a square yard of white flannel to a 3-foot stick and tie a rope to each end of the stick. Drag the cloth over the lawn and leaves, and examine it for ticks that have latched on. Do this several times. To check bushy or grassy vegetation, use a tick "flag," which is similar to the drag but mounted like a flag on a stick. (This tip comes from the Tick Management Handbook, available from the Connecticut Agricultural Experiment Station Web site, www.ct.gov/CAES.) Reduce the number of ticks in your yard by clearing leaf litter, low brush, and tall grasses. You may also want to contact a pest-control professional about chemical options and wildlife control.

Check yourself. If you're in an area inhabited by ticks, check yourself once a day. (Check children and pets in your care, too.) To remove ticks from clothing, you can use an adhesive lint brush or masking or cellophane tape rolled around your hand, sticky side out. Undress and examine your skin, using a mirror (or mirrors) for hard-to-see places, such as the back of the knees, armpits, back of the neck, and scalp. If you find a tick attached to your skin, remove it as soon as possible. (See "How to remove a tick.") Note the date, and save the tick for a month for reference or testing in case you develop symptoms.