Study Links Cat Fleas to Rising Typhus Cases in Texas

As human cases of flea-borne murine typhus continue in South Texas, researchers are examining what role cats and their fleas may play in spreading the disease. In a recent study, scientists at the Texas A&M College of Veterinary Medicine and Biomedical Sciences (VMBS) detected DNA from Rickettsia typhi, the bacterium that causes murine typhus, in cat fleas collected from domestic cats in the Rio Grande Valley, a region with some of the highest rates of human cases in the state.

Murine typhus spreads to humans when flea feces carrying R. typhi enter the body through a bite or mucous membrane, and it can typically be treated with antibiotics. Cases in Texas have risen over the past decade, with more than 6,700 reported in South Texas between 2008 and 2023, according to the Texas Department of State Health Services.

“The last time flea-borne typhus was rampant, rats and rat fleas were the main reservoir and vector,” said Sujata Balasubramanian, first author of the study published in Parasites & Vectors. “Now, there is a layer of cat fleas contributing to this uptick.”

The research team tested fleas from 167 sampled cats and detected R. typhi in fleas from six of them, offering some of the first regional data on the pathogen’s presence in cat flea populations. Fleas and cats also carried Bartonella henselae and Bartonella clarridgeiae, bacteria linked to cat scratch disease. While the study did not examine transmission directly between cats, fleas and people, the findings clarify which pathogens are circulating in local flea populations.

Senior author Sarah Hamer noted that transmission depends on multiple ecological factors: “We must think about the ecology of the disease, which includes the interactions of the right species of flea with cats or opossums—both of which can serve as hosts for the fleas and bacteria. Humans serve as an accidental host when hungry fleas find us instead of an animal.” She added that “the increased abundance of pet cats and stray or feral cats, socioeconomic conditions that prevent access to affordable flea protection on cats, and warming temperatures likely all promote flea infestation of cats and transmission of the bacteria that causes typhus.”

Cats typically do not become seriously ill from R. typhi, but controlling flea infestations remains important for both animal and human health. Researchers say further sampling is needed to understand how risk varies among pet, stray, and feral animal populations, and to track the disease amid ongoing changes in wildlife, climate, and land use.