Xenodiagnosis Tested for Persistent Lyme Disease

Disease-free ticks have been used to detect Lyme disease bacteria in people who continue to experience symptoms such as fatigue or arthritis after completing antibiotic therapy.

The technique, called xenodiagnosis, attempts to find evidence of a disease-causing microorganism indirectly, through use of the natural disease-carrier, in this case, ticks of the Ixodes genus.

Scientists at the Tufts Medical Center (Boston, MA, USA) and their colleagues from other institutions enrolled 36 adult volunteers in the study at locations in Maryland, Connecticut, and Massachusetts. Participants included 10 people with post-treatment Lyme disease syndrome (PTLDS); 10 who had high levels of an antibody against Borrelia burgdorferi after antibiotic treatment; 5 who had erythema migrans, a bull's-eye rash typical of Lyme disease, and had received antibiotic treatment in the past; 1 with erythema migrans who began antibiotic therapy at the time of tick placement; and 10 healthy volunteers.

Participants consented to have up to 30 laboratory-bred, pathogen-free, larval ticks I. scapularis, placed under a dressing. When possible, the ticks were placed near areas where a rash had been observed or near affected joints. After four to six days, investigators removed the ticks and processed them to detect whether any Lyme disease bacteria were present.

Ticks were tested for B. burgdorferi by polymerase chain reaction (PCR), culture, and/or isothermal amplification followed by PCR and electrospray ionization mass spectroscopy. In addition, attempts were made to infect immunodeficient mice by tick bite or inoculation of tick contents. Xenodiagnosis was repeated in seven individuals. Ticks and skin biopsies were extracted using Qiagen DNEasy columns from the DNEasy Blood and Tissue Kit (Qiagen; Valencia, CA, USA).

Not all of the placements yielded enough blood-engorged ticks to perform xenodiagnosis, but 23 volunteers with Lyme disease had at least one tick tested and of these, 19 people tested negative. Two people had indeterminate results, thought to be due to laboratory contamination. Xenodiagnosis was positive for B. burgdorferi DNA in the person with erythema migrans who underwent xenodiagnosis early during therapy, and in a volunteer with PTLDS.

Adriana Marques, MD, the lead author, said, “Xenodiagnosis using ticks to detect B. burgdorferi has been used previously in animal studies, but this is the first time it has been tried in people. Our primary goals in this initial trial were to develop procedures for tick xenodiagnosis and to determine its safety in humans.” The authors concluded that future studies are necessary to determine the incidence of positive xenodiagnostic results for B. burgdorferi after antibiotic treatment, if these results represent viable organisms or remnants of infection, and whether these results can be related to ongoing symptoms in patients after therapy for Lyme disease. The study was published on February 11, 2014, in the journal Clinical Infectious Diseases.

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