In theory, one could simply determine whether B. burgdorferi can be detected in bits of tissue or blood extracted from volunteers with post-treatment symptoms. This is what was done in the mouse studies that I described in my previous post. It's easy to culture B. burgdorferi from untreated mice that have been infected for a long time. However, humans are not mice. Except in those with Lyme arthritis, the spirochete is hard to detect by culture or PCR in patients at later stages of Lyme disease, even in those who haven't taken antibiotics.
In fact, three of the four randomized controlled retreatment trials that I keep on bringing up on this blog included attempts to detect B. burgdorferi in cerebral spinal fluid or blood of PTLDS patients by culture and PCR. No specimen was culture positive except for one, and none were PCR positive. The single positive culture turned out to be a contaminant.
The rest of the scientific literature is littered with claims that Lyme Borrelia can be detected by culture or PCR in blood, urine, or CSF of treated patients. However, critics have raised several concerns about these studies. For instance, alternative explanations for the findings such as contamination or reinfection weren't ruled out.
With all of this as background, Marques and colleagues decided to test a different approach – xenodiagnosis. For this procedure, uninfected ticks are deliberately placed on the skin and left for several days to give them time to take a blood meal. If there are any spirochetes in the skin nearby, they will move towards the feeding site because they are attracted to the tick's saliva. The spirochetes then get drawn into the tick's feeding tube along with the blood meal. The fed ticks are then removed and tested for the presence of B. burgdorferi. The sensitivity of xenodiagnosis can be enhanced by placing multiple ticks to increase the chance that at least one tick will drink blood containing B. burgdorferi. Xenodiagnosis is done routinely with mice in the research setting, and I mentioned in my previous post that B. burgdorferi can be detected in antibiotic-treated mice by xenodiagnosis.
The first thing to do was a pilot study to make sure that the procedure was safe for volunteers. 25 subjects who had been treated for Lyme disease took part in the study. 10 of the 25 had PTLDS. Ten healthy volunteers and one subject with untreated erythema migrans (EM), the skin rash of early-stage Lyme disease, were included in the study.
As for the ticks, the investigators bred and maintained Ixodes scapularis in the laboratory. The ticks were carefully screened to make sure they were free of known infectious agents.
25-30 ticks were placed on each volunteer and covered with a special dressing to keep them in place (see images below). The ticks were left alone for a week so that they could consume a blood meal. Some of the fed ticks were tested for the presence of B. burgdorferi DNA by standard PCR or by a more sensitive technique: isothermal amplification followed by PCR and mass spectrometry (IA/PCR/ESI-MS). The remaining ticks were cultured or were placed on immune-deficient mice to determine whether B. burgdorferi, if present, could be transmitted.
|Figure 1 from Marques et al., 2014. Left panel: ticks covered with a special dressing on forearm. Right panel: feeding ticks attached to forearm, dressing removed.|
So did anyone test positive by xenodiagnosis? Yes. B. burgdorferi DNA was detected in two subjects. One was the subject with untreated EM. This subject served as sort of a positive control. I say "sort of" because antibiotic therapy was started at the same time that the ticks were placed on the EM lesion – it would not have been ethical to delay treatment while the ticks were feeding. B. burgdorferi DNA was detected in two of the ten ticks tested. The subject was tested by xenodiagnosis again seven months later, and all ten ticks that were tested were negative for B. burgdorferi DNA.
The other positive test came from one of the PTLDS subjects. One of the five ticks that were tested was positive for B. burgdorferi DNA. The same subject tested positive by xenodiagnosis again 8 months later: one of three ticks tested positive for B. burgdorferi DNA by IA/PCR/ESI-MS.
Of course DNA doesn't equal viability. The study didn't provide much evidence that the DNA detected in the single case of PTLDS came from spirochetes that were alive at the time that the ticks were placed. A skin biopsy taken from where the xenodiagnostic ticks were feeding was culture negative, as were the fed ticks themselves. The ticks also failed to transmit B. burgdorferi to immune-deficient mice, a process that probably requires live, motile spirochetes. To be fair, this was just a pilot study with the primary goal to assess the safety of xenodiagnosis. Nothing terrible happened to the volunteers, although half experienced mild itching at the feeding site. The investigators are recruiting additional subjects for a larger study to determine whether positive test results by xenodiagnosis are associated with post-treatment symptoms.
Marques A, Telford SR 3rd, Turk SP, Chung E, Williams C, Dardick K, Krause PJ, Brandeburg C, Crowder CD, Carolan HE, Eshoo MW, Shaw PA, & Hu LT (2014). Xenodiagnosis to detect Borrelia burgdorferi infection: a first-in-human study. Clinical Infectious Diseases, 58 (7), 937-45 PMID: 24523212
Bockenstedt LK, & Radolf JD (2014). Xenodiagnosis for posttreatment Lyme disease syndrome: resolving the conundrum or adding to it? Clinical Infectious Diseases, 58 (7), 946-8 PMID: 24523213
Telford SR 3rd, Hu LT, & Marques A (2014). Is there a place for xenodiagnosis in the clinic? Expert Review of Anti-infective Therapy, 12 (11), 1307-10 PMID: 25301228
- Video microscopy of ticks acquiring the Lyme disease spirochete from mice
- Resurgence of Borrelia burgdorferi in mice a year after antibiotic treatment