By Stan Deresinski, MD, FACP, FIDSA
Clinical Professor of Medicine, Stanford University
SYNOPSIS: Three fatal cases of flea-borne typhus, which is endemic in Southern California as well as in Texas and Hawaii, occurred in Los Angeles County in 2022 — the first such fatalities in two decades.
SOURCE: Alarcón J, Sanosyan A, Contreras ZA, et al. Fleaborne-typhus-associated deaths — Los Angeles County, California, 2022. MMWR Morb Mortal Wkly Rep 2023;72:838-843.
The occurrence of three fatalities due to flea-borne typhus in Los Angeles County in 2022, the first such deaths since 1993, prompted this report.
All three patients were Hispanic and included two males (68 and 71 years of age) and a 49-year-old female. All three patients presented with fever, atrial fibrillation, and a petechial eruption on the torso and legs. The patient with the most severe initial presentation was disorientated and hypotensive and had atrial fibrillation with a rapid ventricular response. All three received broad-spectrum antibiotics, but initiation of doxycycline administration was delayed until day 2 in two cases and until day 18 in one. Nonetheless, the patients had downhill courses that variably included multi-organ system failure and hypoxic respiratory failure, with myocarditis, disseminated intravascular coagulation, and hemophagocytic lymphohistiocytosis each occurring in one patient. Death occurred after three, five, and 30 days.
All three patients had positive serum antibody tests for Rickettsia typhi; in two patients, the samples were obtained on the second hospital day, but the results were not available until after the patients’ deaths. In the patient with more prolonged survival, R. typhi deoxyribonucleic acid (DNA) was detected in cell-free plasma with a commercially available next-generation sequencing test.
COMMENTARY
These three infections were caused by caused by R. typhi, resulting from inoculation of the organism by an infected flea of an abrasion, a mucous membrane, or the fleabite itself. The Oriental rat flea, or tropical rat flea, has long been identified as the key vector and accounts for the disease having been referred to as murine typhus. However, the cat flea also is known to play an important role and is, in fact, the predominant vector in suburban areas of the United States. Furthermore, although its primary host is the domestic cat, this flea also is found on opossums, dogs, and rats, perhaps accounting for the need to broaden the name of the infection from murine typhus to flea-borne typhus. In addition to these considerations, this disease also is referred to as endemic typhus.
Flea-borne typhus cases have been subject to mandatory reporting in California since 2010, and the number of cases has been increasing since 2010, reaching 171 in 2022. Most occur in Los Angeles and Orange counties, which together accounted for 720 (96.8%) of the 744 reported cases.1 Approximately one-third of patients require intensive care unit (ICU) care as a consequence of complications, such as aseptic meningitis, seizures, septic shock, and adult respiratory distress syndrome.2 Nonetheless, mortality is uncommon, generally reported to be < 1%. Doxycycline remains a highly effective therapeutic.
In addition to California, flea-borne typhus also occurs in Hawaii and Texas. In the latter, most cases are reported in South Texas, from Nueces County southward to the Rio Grande Valley, but with new areas of endemicity having emerged in Bexar, Harris, and Travis counties in the last 10 years.3
It is likely that only the most severe cases of flea-borne typhus are diagnosed. In most circumstances, confirmation of the diagnosis relies on a fourfold increase in R. typhi immunoglobulin G (IgG) antibody since there is no commercially available organism-specific molecular testing. However, it should be noted that the diagnosis was made belatedly in one patient with the use of an unbiased next-generation plasma DNA sequencing test that is available.
REFERENCES
- California Department of Public Health. Epidemiologic summary of flea-borne typhus in California, 2013-2019. https://www.cdph.ca.gov/Programs/CID/DCDC/CDPH%20Document%20Library/FleaBorneTyphusEpiSummary2013-2019.pdf
- Anstead GM. History, rats, fleas, and opossums. II. The decline and resurgence of flea-borne typhus in the United States, 1945-2019. Trop Med Infect Dis 2020;6:2.
- Texas Health and Human Services. Flea-borne typhus information. Revised May 2010. https://www.dshs.texas.gov/typhus/flea-borne-typhus-information