Rise in Murine Typhus in Galveston County, Texas, USA, 2018

Murine typhus, an undifferentiated febrile illness caused by Rickettsia typhi, is increasing in prevalence and distribution throughout Texas. In 2018, a total of 40 cases of murine typhus were reported in Galveston County. This increase, unprecedented since the 1940s, highlights the importance of awareness by physicians and public health officials.

. Once prevalent in the United States, the disease was nearly eradicated following vector control practices of the 1940s using DDT (2). In 2012, murine typhus was identified in 2 patients from Galveston, Texas. The identification of cases in a city where murine typhus was perceived to have been eliminated prompted the investigation and identification of 12 patients from Galveston County in 2013 (3). Since then, murine typhus has been reported to the Galveston County Health District (GCHD) yearly (1 case in 2014, 8 in 2015, 2 in 2016, and 17 in 2017). Murine typhus has also increased in prevalence and distribution throughout Texas (4). To call attention to this increasingly prevalent disease, we describe an increase of murine typhus reported to the GCHD in 2018.
In Texas, murine typhus is a reportable disease. Our data were collected as part of investigatory efforts of the GCHD to document typhus group rickettsioses (TGR) in Galveston County. The case definition for confirmed TGR includes a clinically compatible illness (acute onset of fever with >1 symptoms including headache, myalgia, anorexia, rash, nausea/vomiting, thrombocytopenia, and elevated hepatic transaminases) with 1 of the following: IgG seroconversion from acute-and convalescent-phase specimens, PCR amplification of R. typhi, immunohistochemical demonstration of the organism within tissue specimens, or culture isolation of R. typhi. We defined probable cases as those having an indirect immunofluorescence assay antibody titer of >1:128 during a compatible illness.
Murine typhus was once prevalent in the United States, with a peak of 5,401 cases in 1944. After eradication efforts using DDT were implemented in 1945, incidence plummeted (e.g., 98 cases in 1956) (2). In the decades that followed, parts of southern California and the most southern counties of Texas remained endemic. In these areas, a transmission cycle involving opossums (Didelphis virginiana) and cat fleas (Ctenocephalides felis) was suspected (1). After the recognized 1045 With the exception of more nausea/vomiting in the probable cases group, there were no significant differences between the groups. †Defined as any aspartate aminotransferase or alanine aminotransferase level over the reference laboratories' upper limit of normal. ‡Defined as <150,000 platelets/L blood. §Patients were asked whether fleas were present in their environment (i.e., yard, neighborhood, house, work) or if they had been bitten by fleas in the 3 weeks before disease onset. ¶Patients were asked whether other wild animals were present in their environment (i.e., yard, neighborhood, house, work). If they answered yes, they were asked to specify the type of animal. #Patients were asked whether dogs or cats were present in their environment (i.e., yard, neighborhood, house, work). If they answered yes, they were asked whether these animals were owned or strays. **Patients were asked whether rodents were present in their environment (i.e., yard, neighborhood, house, work).

RESEARCH LETTERS
reemergence of murine typhus in Galveston, studies have demonstrated that 67% of opossums are seroreactive and 7% of C. felis fleas collected from these animals are infected with R. typhi (5). In contrast, only 0.3% of C. felis fleas collected from feral cats are infected (6).
Although the detailed reservoir-vector dynamics involved with the increasing distribution of R. typhi are yet to be elucidated, the broad geographic range of opossums in North America and the ubiquity of cat fleas parasitizing opossums (7) cause concern for the spread of murine typhus to areas not yet endemic.
The increase in reported cases may be related not only to ecologic factors but also to increased recognition by physicians and enhanced surveillance. Indeed, murine typhus is well recognized at the University of Texas Medical Branch (UTMB), the largest healthcare system in Galveston County. Furthermore, murine typhus is now recognized as a cause of fever in local children. In a study performed at UTMB during 2012-2016, no pediatric patients had yet been identified (8). The later recognition in the pediatric age group was spurred in part by a pediatric case in the fall of 2017, which occurred after local education efforts. Two recently published case series of murine typhus in children may have also contributed (9,10). Finally, since September 2017, the GCHD has distributed several email advisories alerting local physicians of murine typhus.
The rise of murine typhus in Galveston is in step with the apparent increase in distribution across Texas. Awareness of this difficult to recognize undifferentiated febrile illness is paramount not only within Texas but also in other parts of the United States where opossums and cat fleas are distributed.