Study Suggests Lyme Disease Could Be Sexually Transmitted Between Humans


A new study suggests that tiny deer tick bites may not be the only risk factor when it comes to Lyme disease transmission—the disease may be sexually transmitted.

Lyme disease is caused by a corkscrew-shaped (or spirochete) bacteria called Borrelia burgdorferi, which looks very much like syphilis under a microscope. The bacteria is carried by rodents and deer and is transmitted to humans through the bite of blacklegged ticks. Most Lyme disease cases reported to the Centers for Disease Control and Prevention (CDC) occur in the Northeast and upper Midwest, with 96 percent of cases happening in 13 states. Typical symptoms include fever, headache, fatigue, and the bullseye-shaped rash but many of these are missed or mistaken for other common illnesses. If left untreated, infection can spread to joints, the heart, and the nervous system. Though it can be treated with antibiotics if detected, Lyme disease can be hard to diagnose, and the symptoms can mimic other serious disorders, including multiple sclerosis, fibromyalgia, chronic fatigue syndrome, and Alzheimer’s disease. The CDC estimates that 300,000 people in the United States are diagnosed with Lyme disease each year.

The study was presented at the annual Western Regional Meeting of the American Federation for Medical Research, and an abstract of the research was published in the January issue of the Journal of Investigative Medicine. For the study, an international team of researchers divided participants into three groups: a control group that did not have Lyme disease, a random group of men and women who did have it, and a group of married, heterosexual couples who had Lyme disease and engaged in unprotected sex. They then tested vaginal secretions and semen samples. What they found was that the control group did not have the bacteria in their vaginal secretions or semen, but all of the women who had Lyme disease had the bacteria present in their vaginal secretions, and about half of the men showed the bacteria in their semen. Other bacteria found in these fluids, such as those that cause chlamydia and gonorrhea, are easily transmitted from one person to another during sex. The researchers believe the bacteria that cause Lyme could be transmitted that way.  The researchers say their most interesting finding is that one of the married couples had identical strains of the bacteria, suggesting one had transmitted it sexually to the other.

Sexual transmission would mean that a person who contracted Lyme from a tick could give it to his/her partner. It could also mean that now that the disease is so prevalent in humans, it is being spread from one person to another without any ticks involved. As Marianne Middelveen, one of the lead scientists on this research, said in a press release, “It explains why the disease is more common than one would think if only ticks were involved in transmission.” She added, “Our findings will change the way Lyme disease is viewed by doctors and patients.”

Another researcher on the team, Raphael Stricker, put it this way: “There is always some risk of getting Lyme disease from a tickbite in the woods. But there may be a bigger risk of getting Lyme disease in the bedroom.”

Other experts, however, caution that this is one study, and while we should pay attention to its findings, we should not overact. RH Reality Check spoke to William Smith, executive director of the National Coalition of STD Directors (NCSD). He said the results are interesting but noted that the primary finding of sexually transmitted Lyme disease was made because of a single married couple who had the same strand of the bacteria. “This is a very limited study. … Additional inquiry is warranted, but there is no evidence here for even a hint of alarm,” he said.

Smith also pointed out that we know condoms work well to prevent sexually transmitted diseases (STDs) that are transmitted through the exchange of fluids, including vaginal secretions and semen, again, such as chlamydia or gonorrhea. If it does turn out that Lyme disease is among those STDs, condoms will be the best protection for sexually active individuals (especially those who live in heavily wooded areas).

Correction: A version of this article incorrectly noted, in a quote from William Smith of the National Coalition of STD Director, that two people could be bitten by the same tick. This is not, in fact, possible. We regret the error.

In addition, this article has been updated the reflect the CDC’s latest estimates of Lyme disease diagnoses in the United States, which in 2013 was increased from an estimated 30,000 per year to an estimated 300,000 per year.

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  • Cindy Casey Holman

    Lyme Disease is known to be sexually transmitted in canines. Syphilis, a similar spirochetal infection is known to be readily sexually transmitted in humans. The prevalence of Lyme Disease in canines and humans is on a rapid increase. So yeah…I certainly do think these preliminary findings are of great significance. In fact I would hope that the nation’s health organizations, CDC in particular, would lead further investigation. Currently there is no accurate diagnostic test for Lyme Disease and over 50% of cases are missed. It’s extremely important for accurate testing to be developed as well further investigation into modes of transmission.

  • DorothyLeland

    “They could well have been bitten by the same tick,” is a statement that lacks knowledge of how ticks transmit disease. They take a blood meal ONCE during each of the three stages of their life cycle (larval, nymphal, adult). After engorging on your blood, they fall off and won’t feed again until they have progressed to their next stage.

  • vforba

    There is also evidence that it can be passed in utero.