Clinical Pearls & Morning Reports
Published August 1, 2018
Murine typhus, also known as endemic typhus and fleaborne typhus, is a typhus-group rickettsiosis caused by Rickettsia typhi, a gram-negative, obligate, intracellular bacillus. Read the latest clinical problem solving article here.
Q: In what regions of the United States is murine typhus endemic?
A: Murine typhus was prevalent throughout the southeastern United States and California during the first half of the 20th century, with an annual incidence exceeding 5000 cases in the early 1940s. Rats were the primary animal reservoir, with fleas serving as a vector to maintain a rat–flea–rat life cycle. Beginning in 1945, an aggressive campaign to eliminate rat and flea populations was initiated. This effort reduced the annual incidence of murine typhus to fewer than 100 cases by the late 1980s. In 1988, murine typhus was removed from the National Notifiable Diseases Surveillance System but remained endemic to southern and central Texas and southern California. In the past 15 years, there has been a substantial increase in the annual incidence of murine typhus in both locations.
Q: Does murine typhus have a distinctive rash?
A: In the medical literature, the rash in murine typhus is described as beginning on the trunk and spreading outward, sparing the palms and soles. In contrast, the rash in Rocky Mountain spotted fever is described as beginning on the wrists or ankles, spreading to the trunk, and including the palms and soles. In practice, the rashes of both murine typhus and Rocky Mountain spotted fever are variable, and the distribution and evolution of a rash are not reliable means of discriminating between these diagnoses.
A: The symptoms and findings in murine typhus are generally nonspecific. A systematic review of studies involving 2074 patients showed that after an incubation period of approximately 5 to 15 days, the most common symptoms were fever (in >99% of patients), headache (81%), malaise (67%), chills (63%), and myalgias (52%), and the most common findings on physical examination were rash (48%), hepatomegaly (22%), conjunctivitis (18%), and splenomegaly (17%). Common laboratory findings include elevated levels of the aminotransferases (79%) and lactate dehydrogenase (73%), hypoalbuminemia (60%), and thrombocytopenia (42%). The classic triad of fever, headache, and rash is found in approximately one third of patients. In approximately 25% of patients, more severe complications develop, including respiratory failure, aseptic meningitis, seizures, acute renal failure, and septic shock, but the mortality is less than 5% even without antibiotic treatment.
A: The standard for diagnosis of murine typhus is the indirect immunofluorescence assay (IFA). A single titer of 1:128 or higher suggests a probable diagnosis, and an increase in the antibody titer by a factor of four or more over 2 to 4 weeks is diagnostic. Randomized trials are lacking to assess the effectiveness of various antibiotic regimens in patients with murine typhus, but clinical experience supports the use of doxycycline as the first-line antibiotic treatment in nonpregnant adults and children older than 8 years of age. The use of doxycycline is associated with a decrease in the average length of febrile illness from approximately 2 weeks to less than 4 days; it should be continued for 3 days after resolution of symptoms. Ciprofloxacin is also effective and should be used for patients in whom doxycycline is contraindicated.