The already thorny process of diagnosing Lyme disease may have just gotten even hazier.  Lyme is a tick-borne illness that afflicts hundreds of thousands of people every year with a rash of debilitating symptoms.  Three species of bacteria are known to cause the disease in Europe, but only one (Borrelia burgdorferi) lives in North America.  However, after studying over 100,000 samples from American patients with the disease, researchers discovered six specimens that contained a never-before-seen bacterium.  Ticks collected from likely exposure sites also harbored this microbe, which suggests that it may be a new causative agent of Lyme disease.

This finding could eventually represent an important advance in a poorly understood field, but several hurdles stand in the way of therapeutic relevance.  In particular, further testing is needed to conclusively determine if this new microbe causes Lyme disease.  To distinguish causation from mere correlation, researchers may infect a mouse or rabbit with the bacterium and observe whether the animal develops Lyme-like symptoms.  If the animal gets sick, being able to recover the suspected pathogen from the diseased animal would provide additional support for causality.

If true, a new cause of Lyme disease could help to explain why Lyme remains such a nebulous diagnosis. Surprisingly little is known about Borrelia bacteria – especially how they interact with ticks and humans – because they often grow poorly in the laboratory.  As a result, doctors must rely upon highly variable symptoms and indirect measures of infection when offering diagnoses.  Any new data regarding the underlying biology of Lyme disease, therefore, will be a welcome sight to microbiologists and physicians alike.

Acknowledgments: Many thanks to Dr. Daria Van Tyne, a postdoctoral fellow in the Gilmore Lab at Harvard Medical School, for providing her expertise and commentary on the topic.

Managing Correspondent: Christopher Gerry

Original Research Article: Identification of a novel pathogenic Borrelia species causing Lyme borreliosis with unusually high spirochaetaemia: a descriptive study – The Lancet Infectious Diseases

Media Coverage: New Cause for Lyme Disease Complicates Already Murky Diagnosis – Scientific American