Xenodiagnosis for posttreatment Lyme disease syndrome: resolving the conundrum or adding to it?

The first reports of Lyme disease in Connecticut in the mid-1970s, followed by the discovery of its tick-borne etiologic agent, Borrelia burgdorferi, in 1983, has spawned one of the longest controversies in the history of biomedical research [1]. Whereas some clinical signs, such as the hallmark skin lesion erythema migrans (EM), can be explained by the inflammatory response elicited by spirochetes, other features remain enigmatic. Impressive generalized symptomatology can accompany EM and last for weeks to months following therapy and resolution of clinical signs. A minority of people (<10%) continue to experience fatigue, musculoskeletal pain, and/or cognitive dysfunction, a condition called posttreatment Lyme disease syndrome (PTLDS) [2]. The issue at the heart of the current, often acrimonious debate is whether persistent infection drives protracted symptomatology. Four randomized, placebo-controlled trials have evaluated whether extended courses of antimicrobials ameliorate symptoms, ostensibly by eliminating persistent organisms [3–5]. The first 2 trials enrolled seropositive subjects with a previous episode of Lyme disease and seronegative subjects with physiciandocumented EM [3]. These were the most rigorous, as they evaluated therapeutic responses in a large number of subjects and also sought evidence of infection in blood and cerebrospinal fluid using culture and polymerase chain reaction (PCR). The treatment regimen (1 month of intravenous ceftriaxone followed by 2 months of oral doxycycline) was selected because both agents have good tissue penetration (including the central nervous system) and well-documented in vitro and in vivo activity against B. burgdorferi. The results of the intervention were clear: No evidence was obtained for persistent spirochetes, and antimicrobials provided no benefit over placebo. The remaining 2 trials showed either a similar lack of efficacy after 10 weeks of ceftriaxone [4] or only improvement in fatigue after a 4-week course [5], with an unacceptable rate of treatment-associated adverse events. Critics countered that the lack of therapeutic response reflected the persistence of spirochetes in a state that renders them insensitive to antimicrobials. Investigators turned to animal models to examine this possibility (reviewed in [6]). A study in dogs infected using adult ticks found culture positivity and persistence of arthritis in 3 of 12 treated animals [6, 7]. A follow-up study, however, failed to replicate these findings; only DNA was detected and dogs remained culture negative even after prednisone immunosuppression [6, 8]. The first study to use xenodiagnosis, the use of uninfected ticks to detect low-level infection, was conducted in mice [9]. Rare, avirulent spirochetes were visualized by immunofluorescence in tick midgut contents 3 months posttreatment but not thereafter. A different group reported that nymphs molted from xenodiagnostic larvae transmitted DNA, but not spirochetes, to severe combined immunodeficiency (SCID) mice—a truly perplexing result [10]. A rhesus macaque study [11], hailed by some for providing definitive evidence of persistent infection, has evoked considerable skepticism [12]. In 1 of 2 experiments, all monkeys had positive skin biopsy cultures assessed during the first 4 weeks of untreated infection, but postmortem, only 1 of 12 monkeys in each of the treated and control groups was culture positive. A second experiment used xenodiagnosis to detect infection in 5 monkeys. Prior to treatment, infection status was examined by both culture and PCR of skin biopsies but only PCR was positive, even though monkeys were Received 11 December 2013; accepted 16 December 2013; electronically published 11 February 2014. Correspondence: Linda K. Bockenstedt, MD, Section of Rheumatology, Yale University School of Medicine, PO Box 208031, New Haven, CT 06520-8031 (linda.bockenstedt@ yale.edu). Clinical Infectious Diseases 2014;58(7):946–8 © The Author 2014. Published by Oxford University Press on behalf of the Infectious Diseases Society of America. All rights reserved. For Permissions, please e-mail: journals. permissions@oup.com. DOI: 10.1093/cid/cit942