Xenodiagnosis: Using Ticks to Test for Lyme Disease

“Xenodiagnosis was positive for B. burgdorferi DNA in a patient with erythema migrans early during therapy and in a patient with PTLDS [post-treatment Lyme disease syndrome],” writes Marques from the National Institute of Allergy and Infectious Diseases at the National Institutes of Health. However, there wasn’t enough evidence to conclude that viable spirochetes were present in either patient.

Researchers have allowed ticks to feed on animals while conducting animal studies. “Xenodiagnosis has long been used in Lyme disease research to provide definitive evidence of a host’s infection status,” explains Turk and colleagues in a recently published paper, Xenodiagnosis Using Ixodes scapularis Larval Ticks in Humans.

But Marques’ endeavor was the “first clinical study of the use of I. scapularis larva for the xenodiagnosis of B. burgdorferi infection in humans.”

How the Tick Testing Method Works

How to get a tick to bite a human for this test was described in the journal Methods of Molecular Biology. The larval ticks were uninfected. “Specific pathogen-free I. scapularis larval ticks were obtained from Dr. Sam Telford from a laboratory-maintained tick colony at Tufts Veterinary School,” Turk states.

The ticks were free of B. burgdorferi, Babesia spp., Anaplasma phagocytophilum, Borrelia miyamotoi, Bartonella spp., Rickettsia spp., deer tick virus, orbiviruses, Francisella tularensis, spirochetes, and alphaproteobacteria.

The larval ticks were applied to the subject using a wooden toothpick. “If any tick escapes from the placement site or vial during the process,” Turk states, “a piece of adhesive tape can be used to rapidly capture the tick.” An adhesive liner held the ticks in place.

The subject was sent home with specific instructions on how to care for the site where the tick attached.

Patient Instructions for Xenodiagnosis

Your dressing is to remain in place for 4–6 days. The dressing keeps the ticks in place. Please do not open or remove the dressing during the study period.

Do not scratch the dressing site if it itches. You may take oral diphenhydramine (Benadryl) for itching.

When showering, please cover the dressing site with AquaGuard. Remove the AquaGuard promptly after showering. Gently pat dry the dressing if necessary.

Please check that the dressing is firmly in place. Refrain from aerobic exercise or any activity that would induce heavy perspiration.

Check the dressing daily to make sure all edges are sealed. Call the study personnel if there is a problem with the dressing.

What If a Tick Escapes?

Not to worry if you lose a tick, writes the author. “Loss of ticks should not pose a risk to either the participant or other people in contact with the subject.” He elaborates, explaining:

Ixodes ticks require high moisture content and would not survive in an indoor or urban setting for more than 1 or 2 days.

Unfed ticks would be uninfected and at most, would attach at a site other than the xenodiagnostic site on the participant or, perhaps, on a family member.

Fed ticks are not expected to feed again for 3 – 6 months.

Current Status and Limitations

The authors point out that “Xenodiagnosis using Ixodes ticks in humans remains an experimental method and must be performed under an approved clinical research protocol.”

This method is not available for routine clinical use. It exists primarily as a research tool to definitively establish infection status in patients where standard serologic testing may be unreliable.

The fact that xenodiagnosis detected B. burgdorferi DNA in both a patient with early Lyme disease and a patient with post-treatment Lyme disease syndrome suggests that spirochetes may persist despite antibiotic therapy. However, detection of DNA does not confirm the presence of viable, culturable bacteria.

Why This Method Matters for Research

Xenodiagnosis provides a unique window into persistent infection that other testing methods cannot offer. Standard serologic testing detects antibodies, not active bacteria. PCR testing of blood or tissue may miss low-level infection. Culture is notoriously difficult for Borrelia burgdorferi.

By allowing uninfected larval ticks to feed on patients, researchers can determine whether spirochetes are present and accessible to feeding ticks—even when other testing methods fail to detect infection.

The positive xenodiagnosis in a patient with post-treatment Lyme disease syndrome is particularly significant, as it suggests spirochetes may persist after standard antibiotic courses in at least some patients.

Frequently Asked Questions

What is xenodiagnosis for Lyme disease?
Xenodiagnosis is an experimental method where uninfected larval ticks feed on a patient to detect Borrelia burgdorferi infection. The ticks are then tested for bacterial DNA after feeding. It’s used in research, not routine clinical practice.

Is tick testing for Lyme disease available to patients?
No. Xenodiagnosis using larval ticks remains an experimental research method. It must be performed under an approved clinical research protocol and is not available for routine diagnostic use.

How accurate is xenodiagnosis?
Xenodiagnosis detected B. burgdorferi DNA in patients with both early Lyme disease and post-treatment Lyme disease syndrome. However, detecting DNA does not confirm viable, culturable bacteria are present.

What if the tick escapes during testing?
Escaped ticks pose minimal risk. Ixodes ticks require high moisture and won’t survive indoors for more than 1-2 days. Unfed ticks are uninfected, and fed ticks won’t feed again for 3-6 months.

Does xenodiagnosis prove persistent infection after treatment?
Xenodiagnosis detected B. burgdorferi DNA in a patient with PTLDS, suggesting spirochetes may persist after treatment. However, DNA detection doesn’t definitively prove viable bacteria are present or causing symptoms.

Clinical Takeaway

Xenodiagnosis represents an innovative approach to detecting Borrelia burgdorferi infection when standard testing methods fail. By allowing uninfected larval ticks to feed on patients, researchers can determine whether spirochetes are present and accessible—even when serology, PCR, and culture produce negative results. The method’s most significant finding came from detecting B. burgdorferi DNA in a patient with post-treatment Lyme disease syndrome. This suggests spirochetes may persist after standard antibiotic courses in at least some patients, though detecting DNA does not definitively prove viable bacteria are present. For patients, this research validates what many have long suspected: negative test results do not exclude persistent infection. Standard serologic testing detects antibodies, not bacteria. PCR may miss low-level infection. Culture is extremely difficult for Borrelia. Xenodiagnosis fills a diagnostic gap by directly assessing whether spirochetes are present and accessible to feeding ticks. However, this method remains experimental and unavailable for routine clinical use. It exists as a research tool, not a diagnostic option patients can request. The real value lies in what it reveals about testing limitations. If xenodiagnosis can detect infection when other methods fail, this confirms that negative standard tests cannot definitively rule out Lyme disease—particularly in patients with persistent symptoms after treatment.