The CDC says absolutely not. Research shows it does not occur in animal models. It turns out humans, at least most of us, aren’t rodents. Admittedly I have not studied rat copulation but on its face the anatomy and physiology are different. The amount of body fluid exchanged, the presence of a large mucous membrane, methods and time are different for starters. Observations have been made that Lyme spirochetes have been recovered from human female genital secretion and to a lesser extent male. This is not a surprise since male seminal fluid contains natural antibiotic substances. The paper in 2014 states the same strains of Lyme were found in both sexual partners. The findings are interesting but not proof. Alternate explanations are feasible: husband and wife did the same activities and were exposed to the same ticks. Retrospective data may be unreliable. We don't know if spirochetes in genital secretions are alive, dead or viable. When passed from a tick spirochetes are wrapped in a protective protein and secreted below the outer epidermis; we don't know if such steps are necessary for transmission. On the other hand, it is clear that vertical transmission occurs: a pregnant mother can clearly transmit Lyme to her unborn child.
The CDC claims that epidemiology does not support the notion of sexual transmission. I don’t think we have data to support that claim. Most Lyme infected individuals are asymptomatic and most symptomatic Lyme patients are misdiagnosed. Lyme is slippery and not easy to track like STDs with known calling cards – like gonorrhea. We really don’t know how many Americans are infected with Lyme. There are other STDs that have been missed because of their subtly, like HPV. It took decades for doctors to realize that the majority of the sexually active population is infected since the only manifestation in most cases is cervical cancer. The epidemiology argument does not hold water for now.
We are left with considerations of biological plausibility. The argument is made that Lyme is like syphilis. Lyme is a vector borne zoonosis. It resides in host animals and is occasionally passed to humans by specific ticks; the humans become accidental hosts. It is different from syphilis which is solely sexually transmitted. The two come from different family trees: one is from the genus Borrelia and the other Treponema. Biologically they are different. The two pathogens evolved along very different lines. After all, syphilis is not transmitted by ticks but humans are the only host of syphilis; this argument is weak. We have to consider other biological specificity. Malaria is transmitted by only one species of mosquito and plague by a specific rate flea. Well – this applies to vector specificity. We know there is Lyme vector specificity. This doesn’t prove anything. The question is: Is it biologically plausible for a vector borne organism to be spread by some other means, such as physical or sexual contact? The answer is maybe. Pathogens adapt. For example, the bubonic plague transmitted only by rat fleas evolved. It became the pneumonic plague transmitted by a cough.
There are Lyme cases that are difficult to explain without conjuring the hypothesis of sexual transmission. In my practice these seem rare. Two recent patients tested positive for Lyme, one male and one female. One is a city apartment dweller who never goes outside. Her husband is an outdoorsman. The other lives in Colorado, a Lyme free zone and never ventures into the great outdoors. He became ill after an encounter with a female partner who resides in the East Coast. Interestingly, the female was suffering with a flulike illness at the time of the encounter. It is tempting to latch on to data from the 2014 study. I am not there yet.
I tell my patients not to panic. Sexual transmission if it does occur may be rare. I think. We don’t really know: is Lyme like hepatitis B – sexually transmitted or hepatitis C – rarely sexually transmitted?
I think it is irresponsible to categorically stake out a position on this issue. The first order of business is an intelligent proportional, science-based discussion. Perhaps this doesn’t help patients who want a clear yes or no. Perhaps other interested parties who will happily meet that need. Not me.
Patients ask: are you a Lyme literate doctor. I answer: that is not important. The question is, are you a Lyme literate patient? It seems very few things Lyme are black or white. If you don't like dealing with murky shades of gray you picked the wrong disease.
It is important for us to acknowledge that which we know and that which we do not.