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Lyme disease is the most common insect-borne illness in the U.S., by far. The Centers for Disease Control and Prevention logs some 30,000 cases each year, and the agency says tenfold more go unreported.
With so many people affected, it’s little wonder how much misinformation there is on the subject. Depending on where your web searching takes you, you might be convinced that the disease can be sexually transmitted like Zika virus (it can’t), or spread through contaminated deer meat (not true), or that pretty much any tick bite guarantees that you’ll be infected (it doesn’t).
You might also think the question of how Lyme disease can and can’t spread is a silly one to ask at the end of summer. Don’t ticks die off, along with all other biting insects, once autumn arrives?
Unfortunately, they don’t.
In fact, adult tick populations tend to swell in midfall—especially in the Northeastern states, where Lyme is most prevalent. “Things quiet down in August and September,” says Thomas Mather, director of the University of Rhode Island TickEncounter Resource Center and one of the nation’s foremost tick experts. “But then bam! In about the second week of October, we get a ticknado.”
Mather says that because most people aren’t aware of this surge, they become complacent once the temperature drops. Flea collars come off, insect repellents get packed away, and average woods-walking humans stop checking for ticks. “It’s a battle to keep this stuff in people’s minds once you hit September,” Mather says.
To help with that battle, and to dispel some persistent myths, Consumer Reports compiled a rundown of what science says about how you can and can’t catch Lyme disease, along with some reminders about how to stay safe this fall.
How Lyme Disease Does NOT Spread
Let’s start with the myths.
Sexual transmission: A 2014 study found Borrelia burgdorferi—the bacteria that transmits Lyme disease—in vaginal secretions and semen from infected study participants, but not from uninfected control groups. The study’s authors noted that the bacteria itself resembles the syphilis bacteria (both are spiral-shaped), and suggested that their results point to sexual transmission. But finding infectious microbes in the genital tract is not the same as proving that they were deposited there during sex. So far, the CDC says—and most experts agree—that there is no solid epidemiological evidence to substantiate this claim.
Blood and breast milk: No cases of Lyme disease have been linked to breast milk or blood transfusions. However, the bacteria have been found in stored blood, and the American Red Cross advises anyone who has tested positive for Lyme disease to hold off donating until their treatment is complete and their tests come back negative.
Animals and other insects: It’s true that forest critters and household pets can bring disease-laden ticks into your yard, and thus into close proximity with you. It’s also true that dogs can develop the actual disease. But none of these animals can pass the bacteria directly to you. Neither can mosquitoes, fleas, lice, or any tick species other than the two noted above. (The Lone Star tick, American dog tick, and Rocky Mountain wood tick have not been shown to pass Lyme. Only the black-legged varieties have.)
Eating meat: There is no credible evidence that Lyme can spread through contaminated food, including deer or squirrel meat. You’ll still want to cook your meat thoroughly, of course. And also be mindful of ticks when you are hunting or dressing deer to eat.
How Lyme Disease Spreads
The list of ways you can catch Lyme disease is conspicuously shorter, especially given how many people are infected each year. The illness is caused by B. burgdorferi, bacteria that can be passed to humans from just two types of tick: the black-legged or “deer” tick (Ixodes scapularis) in the Northeastern U.S., and the Western black-legged tick (Ixodes pacificus) along the West Coast.
When they bite, infected ticks can pass the bacteria to humans, forest critters, and household pets alike. For humans, the bugs make their way onto clothing and into one of the body’s dark, moist areas, namely the scalp, groin, or armpit. (They usually make this journey from the ground up, Mather says. The notion that they drop down from trees is a popular but incorrect one.)
For the most part, doctors and scientists believe that it takes 36 to 48 hours (or longer) for the bacteria to pass from a tick’s body into yours. Like most ticks, the black-legged variety can stay attached to your skin for much longer than that. Once it finds a warm, dark spot to feed, the bug secretes two chemicals: an anti-inflammatory compound that anesthetizes you to the bite, and a gluelike substance that enables it to stay attached.
Most humans are infected by immature ticks called nymphs, which tend to feed during the spring and summer months. Because these babies are very small (no bigger than a poppy seed) and very difficult to see, the warmer season is generally recognized as the most dangerous time for Lyme disease transmission: You can’t remove what you don’t detect, so once it latches on, a nymph stands a good chance of remaining attached long enough to infect you.
But adult ticks can transmit B. burgdorferi, too, and as noted above they tend to be active in the cooler months—from midautumn into early winter.
Pregnancy and Protection
There is one tick-free route by which Lyme-causing bacteria can be transmitted: It can cross from an infected mother into the placenta. There have been documented cases of stillbirths resulting from such transmissions. But the available evidence indicates that when a pregnant woman receives proper antibiotic therapy, her fetus is unlikely to be affected by the infection.
The best way to protect yourself from Lyme disease is to avoid tick bites as much as possible. See our expert tips for protecting your yard and your skin. (Our testing indicates that any repellent that works against mosquitoes should also work against ticks.) And you can learn the proper technique for removing the ticks you do find.
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