Single-tick experiments uncover shifting immune defenses during earliest stages of bacterial infection

by University of South Alabama

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Bacteria from the Gulf Coast tick can be transmitted to its host within one hour of attachment before spreading rapidly to lymph nodes and internal tissues, according to new research by a recent graduate of the Frederick P. Whiddon College of Medicine.

Chanakan "Nam" Suwanbongkot, Ph.D., published findings from her dissertation research in the journal PLOS Pathogens, advancing understanding of how tick-borne bacteria enter the body and interact with the immune system. Her study, conducted in the laboratory of Kevin Macaluso, Ph.D., professor and chair of microbiology and immunology at the University of South Alabama, used a single-tick model designed to more closely reflect how people are naturally exposed to tick-borne pathogens.

"Tick-borne diseases, including spotted fever group Rickettsia, have become an increasingly important public health concern in the United States over the past few decades," Suwanbongkot said. "Although these diseases occur worldwide and reported cases of rickettsioses are rising, little is known about tick-to-vertebrate transmission biology."

The Gulf Coast tick is the primary vector for Rickettsia parkeri, the bacterium that causes R. parkeri rickettsiosis. R. parkeri can cause febrile illness and a characteristic eschar—a dark, necrotic lesion that develops at the site of a tick bite.

The research findings offer new insight into the earliest stages of infection and a foundation for future research into tick-borne disease prevention.

"This work really pushes the field forward with a thorough analysis of tick transmission of a bacterial pathogen," Macaluso said. "I was impressed by Nam's ability to develop the bioassay and orchestrate the experiments with collaborators, all leading to an impactful publication."

A single tick models natural exposure

Many studies of Rickettsia infection use needles to introduce bacteria into the body, an approach that cannot fully capture the interactions among the tick, the pathogen and the host during a natural bite. To address this gap, Suwanbongkot and her collaborators developed a model using a single infected tick to study bacterial transmission and the host's immune response at the attachment site.

Because tick saliva can influence the host's immune response, this approach allows researchers to investigate aspects of natural transmission that needle-inoculation models may not capture. Additionally, the bacterial load delivered by the tick was substantially lower than the doses typically used in needle-inoculation studies.

The team also tracked changes in skin inflammation and immune activity over time. Although inflammation developed as ticks fed regardless of their infection status, infected skin showed a distinct immune response later in the feeding process. By six days after tick attachment, macrophages were the dominant immune cell type at the bite site, accompanied by changes in inflammatory signals consistent with a delayed pro-inflammatory response to infection.

"Suwanbongkot's study employed a novel single-tick feeding model that reflects natural human exposure," said Robert Barrington, Ph.D., professor of microbiology and immunology. "Her study advances our understanding of the earliest events in tick-borne infections and provides a valuable foundation for future studies aimed at preventing tick-borne disease."

Publication details

Chanakan Suwanbongkot et al., Spotted fever group Rickettsia infection kinetics and cutaneous host response during single tick feeding events, PLOS Pathogens (2026). DOI: 10.1371/journal.ppat.1014626

Journal information: PLoS Pathogens

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Infectious diseasesAllergy and immunologyCommon illnesses & Prevention Provided by University of South Alabama Who's behind this story?

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