Cat fleas in south Texas carry murine typhus pathogen, study finds

A study from the Texas A&M College of Veterinary Medicine and Biomedical Sciences (VMBS) detected DNA from Rickettsia typhi, the bacterium that causes flea-borne murine typhus, in cat fleas (Ctenocephalides felis) collected from domestic cats in the Rio Grande Valley, a region that consistently records some of the highest human murine typhus case counts in Texas.¹ The findings offer some of the first data on the pathogen's presence in cat flea populations in the area and could add another layer to what clinicians understand about the disease's transmission cycle.

A shifting reservoir

Flea-borne murine typhus infects humans when flea feces containing R. typhi enter the body through a bite site or mucous membrane. The infection is generally treatable with antibiotics, but its incidence has climbed steadily across South Texas over the past decade. More than 6,700 cases were reported in the region between 2008 and 2023, according to the Texas Department of State Health Services.²

The vector picture has changed since earlier outbreaks. "The last time flea-borne typhus was rampant, rats and rat fleas were the main reservoir and vector," said Sujata Balasubramanian, MS, PhD, an associate research scientist at VMBS and the study's first author.² "Now, there is a layer of cat fleas contributing to this uptick."

What the team found

Testing fleas collected from 167 domestic cats, researchers detected R. typhi in fleas removed from six animals. The team also identified Bartonella henselae and Bartonella clarridgeiae in fleas and cats, both associated with cat scratch disease, another zoonotic infection.¹

“There are only a few places in the US where murine typhus is recognized to be transmitted with some regularity and, unfortunately, that includes South Texas,” said Sarah Hamer, MS, PhD, DVM, DACVPM(epi), a professor in the VMBS Department of Veterinary Integrative Biosciences.² “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.”

The study did not directly examine transmission among cats, fleas and people, but it clarifies which pathogens are circulating in local flea populations where human cases keep occurring. The work underscores a One Health approach that connects animal, human and environmental health.

Warming temperatures, growing pet and stray cat populations, and limited access to affordable flea protection likely all contribute to continued transmission, Hamer noted.

The clinical takeaway

Cats rarely become seriously ill from R. typhi, and the researchers stress the findings do not paint cats as a threat. The message for practitioners is about parasite control. Hamer recommends keeping cats indoors and away from wildlife, and partnering with veterinarians on consistent flea and tick control straightforward counseling points that carry public health weight in endemic regions.

“Fleas and other ectoparasites can spread disease agents that not only make our pets sick, but they can make us sick as well,” Hamer concluded. “Keeping cats indoors where they can’t interact with wildlife and working with your veterinarian to provide flea and tick control for cats can help minimize chances of disease transmission.”

The authors describe the study as a starting point and call for expanded surveillance across pet, stray and feral populations.

References

1. Balasubramanian S, Zecca IB, Koger A, Hamer SA. Rickettsia typhi, Bartonella henselae, and related zoonotic agents in fleas from domestic cats (Felis catus) from the Rio Grande Valley, Texas. Parasit Vectors. 2026;19(1):281. doi:10.1186/s13071-026-07421-1
2. Haines C.Feline fleas carry bacteria linked to human disease in South Texas, study finds. Texas A&M University. July 2, 2026. Accessed July 8, 2026. https://stories.tamu.edu/news/2026/07/02/feline-fleas-carry-bacteria-linked-to-human-disease-in-south-texas-study-finds/