Ticks have a bad reputation because they are thought to cause Lyme disease (LD). This is only partly true; in fact, ticks are simply carriers of bacteria known as Borrelia burgdorferi that are the true disease-causing agents. Ticks deliver these bacteria when they bite humans. Beyond B. burgdorferi, closely related bacteria B. afzelii and B. garinii are also carried by ticks and can cause LD. All of these bacteria are obligate parasites, meaning that their survival and reproduction depend on exploiting their relationship with a host.
This article investigates how the immune status of an individual impacts the pathogenicity (an organism’s potential of causing disease) of LD-causing bacterium in infected ticks. Humans are not defenseless against Borrelia infection; once an individual has been infected with one species of LD-causing bacteria, they cannot be re-infected by the same species; however, they remain susceptible to infection by different species. The researchers wanted to learn how the human host’s blood, containing immune factors developed in response to different infections, could affect bacteria in the tick and alter the course of the disease. They were the first to show that immunity to LD-causing bacteria actually occurs in the feeding tick, prior to transmission, through neutralization mechanisms. Moreover, they found infected host blood impacted the disease-causing bacteria differently depending on the strain of bacteria. Blood from an infected host negatively impacted infection of similar bacterial strains, thus protecting the host from super-infection. Blood from infected hosts promoted infection by different strains.
These findings can be used to develop immunity-based LD treatment options, and also contribute to epidemiology-based studies that analyze the distribution of LD, based on a population’s specific immune characteristics.
Summary by: Mairin Hogan
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Infection history of the blood-meal host dictates pathogenic potential of the Lyme disease spirochete within the feeding tick vector
Bharti Bhatia, Chad Hillman, Valentina Carracoi, Britney N. Cheff, Kit Tilly, Patricia A. Rosa