A while ago we reported on efforts to use the technique of xenodiagnosis to detect Lyme disease. The hope was that this slightly bizarre way of testing could help confirm a diagnosis in humans who were symptomatic of Lyme disease but who have otherwise returned negative results on Lyme disease blood tests. A new study suggests, however, that xenodiagnosis for Lyme disease in humans may be no better really than currently available tests.
This latest research looked at the safety and efficacy of xenodiagnosis, a technique where uninfected ticks are allowed to bite those suspected of infection in order to see if they themselves become infected. Thirty-six volunteers had 25-30 Ixodes scapularis ticks placed on their skin, with the ticks remaining attached and covered with a special dressing until they had finished feeding. Ticks were removed a few days after application and were then incubated for up to 14 days to allow any bacteria to develop.
Ten of the volunteers had never had Lyme disease, while the remaining 26 had either persistent symptoms after Lyme disease treatment, or still had irritation at the original site of the bite, or high levels of antibodies even where treatment appeared successful.
No Viable Bacteria in Xenodiagnosis for Lyme
Ticks were then tested for the Lyme disease bacteria, Borrelia burgdorferi, using polymerase chain reaction (PCR), culture, and isothermal amplification followed by PCR and electrospray ionization mass spectroscopy. Immunodeficient mice were also exposed to the potentially infected ticks and injected with the ticks’ contents in order to see if they became infected. Seven of the volunteers underwent a second round of xenodiagnosis.
In all cases the volunteers tolerated xenodiagnosis and no severe adverse effects were observed. Mild itching at the site of tick bite was the most commonly reported discomfort. Results were negative for 16 patients with post-treatment Lyme disease syndrome (PTLDS) and/or high C6 antibody levels. Results were also negative in 5 patients who had completed antibiotic therapy for erythema migrans.
One patient who had erythema migrans (the Lyme disease rash) early during therapy tested positive for B. burgdorferi DNA, as did a patient with PTLDS. However, in neither patient was there enough evidence to conclude that viable spirochaetes were present, meaning that the infection was not ongoing.
Xenodiagnosis Safe, but is it Useful?
Xenodiagnosis has been used successfully to diagnose persistent Lyme disease infection in animals, as well as to detect other infections such as Chagas disease. This research suggests, however, that xenodiagnosis for Lyme disease still needs further investigation before its use is recommended. Some 10-20% of people who get Lyme disease continue reporting pain, fatigue, aches and other symptoms of the infection even after it appears that the infection has been eradicated and xenodiagnosis could offer support for a diagnosis of persistent infection undetectable using ELISA and Western blot.
The main purpose of this study was to see if xenodiagnosis was safe and viable in humans, which it appears to be. Further studies looking at the usefulness of the technique will now be carried out.
Adriana Marques, Sam R. Telford III, Siu-Ping Turk, et al. Xenodiagnosis to Detect Borrelia burgdorferi Infection: A First-in-Human Study. Clin Infect Dis. 2014 Feb 11.