By Stan Deresinski, MD, FACP, FIDSA
Synopsis: Cases of flea-borne typhus are dramatically increasing in Texas.
Sources: Davies M. Flea-borne typhus is making a comeback in Texas. Texas Public Radio. Sept. 7, 2025. https://www.tpr.org/bioscience-medicine/2025-09-07/flea-borne-typhus-is-making-a-comeback-in-texas
Texas Department of State Health Services. Flea-borne Typhus. https://www.dshs.texas.gov/notifiable-conditions/zoonosis-control/zoonosis-control-diseases-and-conditions/flea-borne-typhus
Texas is the flea-borne typhus “king” of the United States. More than 6,700 cases of murine typhus were reported in Texas in 2008-2023, rising during that time from a low of 135 in 2010 to 835 cases in 2023. Approximately 70% of the 6,700 cases were hospitalized, and 14 fatalities were attributed to the disease. In 2024, there were 847 cases and, unfortunately, 2025 is on a pace to break the 2024 record with 682 provisional cases reported through August 31. Since infections usually peak in late summer and autumn, the number is bound to exceed the prior one-year record.
Most Texas cases occur in South Texas from Nueces County down southward to the Rio Grande Valley. In addition to the marked case increase over the last 15 years, new areas of endemicity have emerged. These include the Dallas-Fort Worth metroplex and the Greater Houston area, as well as Bexar, Travis, and several other counties.
Commentary
The natural reservoirs of Rickettsia typhi infection are rats and their fleas, but other animals, including domestic cats, also may transmit flea-borne typhus, with the rat flea (Xenopsylla cheopis) and the cat flea (Ctenocephalides felis) being the most common vectors. The mouse flea, Leptopsyllia segnis, also is a potential vector. The organism is transmitted via flea feces with defecation occurring while the flea bites. Besides Texas, most autochthonous cases in the United States have occurred in California and Hawaii. It is considered endemic in areas of Los Angeles and Orange counties.
After a usual incubation period of six to 14 days, patients develop fever, headache, and myalgias. Rash may appear approximately five days after symptom onset. The rash is centripetal, starting on the trunk and then spreading to the extremities. Most cases are mild, although severe cases, including fatal ones, may occur. The presence of G6PD deficiency may be associated with increased severity of the infection.
The diagnosis is confirmed most often by serological testing, but polymerase chain reaction testing also may be available. The standard treatment is doxycycline administration, and this should be initiated empirically in suspect cases rather than awaiting the results of diagnostic testing. Symptoms rapidly resolve with therapy.
Stan Deresinski, MD, FACP, FIDSA, is Clinical Professor of Medicine, Stanford University.
