NIAID Study Compares Virulence of Lyme Disease Bacterium in Fed, Unfed Ticks











NIAID Study Compares Virulence of Lyme Disease Bacterium in Fed, Unfed Ticks

A new NIAID study suggests that Borrelia burgdorferi infectivity depends in part on previously unidentified changes that occur when deer ticks take a blood meal from a mammal. B. burgdorferiis the spirochetal bacterium that causes Lyme disease. The study shows that as few as 30 spirochetes from fed ticks can cause infection when injected in mice, whereas an inoculum containing 10,000 spirochetes from unfed ticks is largely noninfectious. Scientists know that B. burgdorferi spirochetes adapt to different environments during transmission from ticks to mammals. They also know that ticks need a blood meal for spirochetes to replicate and thrive, but they didn’t know the absolute extent to which the blood meal influenced virulence in those spirochetes.

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NIAID Study Compares Virulence of Lyme Disease Bacterium in Fed, Unfed Ticks

A new NIAID study suggests that Borrelia burgdorferi infectivity depends in part on previously unidentified changes that occur when deer ticks (Ixodes scapularis) take a blood meal from a mammalian host. B. burgdorferi is the spirochetal bacterium that causes Lyme disease. The study, published online March 7, 2016, in Parasites and Vectors, shows that as few as 30 B. burgdorferispirochetes from fed ticks can cause infection when injected in mice, whereas an inoculum containing 10,000 spirochetes from unfed ticks is largely noninfectious.

Background

Prior to this study, scientists knew that B. burgdorferi spirochetes successfully adapt to different environments during transmission from tick vectors to mammalian hosts—a process that typically takes at least 48 hours. They also knew that ticks need a blood meal for spirochetes to replicate and thrive, but they didn’t know the absolute extent to which the blood meal influenced virulence in those spirochetes.

The results: Of 65 mice injected with viable B. burgdorferi from unfed ticks, just one became infected. Of 37 mice injected with similar numbers of spirochetes from fed ticks, 35 became infected.

Next Steps

Directly comparing the gene products that spirochetes make in ticks before and after feeding should identify critical components of the adaptive response that spirochetes use to infect mammals. A better understanding of spirochetes in the tick vector will help in the design of measures to prevent and treat Lyme disease.

Reference:

Kasumba et al. Virulence of the Lyme disease spirochete before and after the tick blood meal: a quantitative assessment. Parasites and Vectors DOI: 10.1186/s13071-016-1380-1 (2016).