# First detection of rickettsiae in a US chigger population and the potential risk to people

> **NIH NIH R03** · NORTH CAROLINA STATE UNIVERSITY RALEIGH · 2022 · $87,502

## Abstract

Project Summary/Abstract
 Trombiculid mites belonging to several genera (Ascoschoengastia, Eutrombicula,
Neotrombicula, Leptotrombidium, etc.) demonstrate a unique mode of parasitism compared
to other medically important arthropod vectors. Particularly, the genus Leptotrombidium is
the exclusive biological vector of scrub typhus, caused by Orientia tsutsugamushi (Ot), an
obligate intracellular Gram-negative bacterium closely related to the genus Rickettsia
(Rickettsiales: Rickettsiaceae). This disease is a significant source of morbidity and
mortality; an estimated billion people are at risk and approximately one million cases are
reported each year. Scrub typhus occurs in Korea, Japan, throughout southern Asia, the
Asian-Pacific region, and northern Australia. More recently, scrub typhus reports in the
Middle East, southern Chile, and Africa have reshaped our thinking about the
epidemiological of this disease, suggesting it has a wider geographical distribution. Despite
the growing number of studies and discoveries of chigger-borne human disease outside of
the Tsutsugamushi Triangle, the role of chiggers in human infection of rickettsial pathogens
in the US is still a total unknown. We have preliminary data that chiggers collected from NC
are infected with Rickettsia species. Examining the prevalence of rickettsiae in chiggers is
significant because chiggers in the US feed on the same animal reservoirs as ticks that carry
and transmit human diseases, and there is the potential that human diseases attributed to
ticks might be from chiggers. In this proposal, we will detect and determine the prevalence
of rickettsiae DNA in chigger samples from different rodent species and for free-living
(unfed, host-seeking) chiggers in North Carolina. Also, investigate for the first time the
bacterial microbiome of chiggers in the North Carolina. This study will investigate the impact
of host feeding versus transovarial transmission on the chigger pathogen, the association of
bacteria with specific mite and animal species, and the relationship between chigger
microbiome composition, endosymbiont interactions, and vector competency. This
proposal exactly fits the goal of the R03 grants program, assessing the health risk to
humans of chigger bites, which is a complete black box (has never been conducted
before in the US). Similar studies on other continents, including South America, have
found chiggers to harbor human pathogens.

## Key facts

- **NIH application ID:** 10352841
- **Project number:** 1R03AI166406-01
- **Recipient organization:** NORTH CAROLINA STATE UNIVERSITY RALEIGH
- **Principal Investigator:** Loganathan Ponnusamy
- **Activity code:** R03 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $87,502
- **Award type:** 1
- **Project period:** 2021-11-01 → 2023-10-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10352841

## Citation

> US National Institutes of Health, RePORTER application 10352841, First detection of rickettsiae in a US chigger population and the potential risk to people (1R03AI166406-01). Retrieved via AI Analytics 2026-05-27 from https://api.ai-analytics.org/grant/nih/10352841. Licensed CC0.

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