Murine Typhus
Murine typhus is an uncommon flea-borne infectious disease caused by Rickettsia typhi. The illness is less commonly diagnosed in the United States than in the developing world because of improvements in hygiene and rat control efforts.
Murine typhus is caused by Rickettsia typhi, a gram-negative, obligate, intracellular bacillus. Murine typhus is primarily transmitted by the rat flea, Xenopsylla cheopis. Additional vectors include the cat flea, Ctenocephalides felis and the mouse flea, Leptopsyllia segnis. Fleas remain permanently infected with Rickettsia typhi and their lifespan is not shortened by infection. Humans become infected by inoculation of infected flea feces in bite wounds. Incubation period lasts from 5 to 15 days.
Murine typhus is typically a mild illness. Signs and symptoms are generally nonspecific. The most common symptoms are fever, headache, malaise, chills and myalgias. About half of patients develop a rash near the end of the first week of illness.The rash typically begins as a maculopapular eruption on the trunk and spreads peripherally, sparing the palms and soles. However, the pattern of rash development is too variable to be diagnostic. The classic triad of fever, headache and rash is present in about one third of patients. Patients with glucose-6-phosphate dehydrogenase deficiency (G6PD) and advanced age are more likely to develop neurologic and cardiac complications. G6PD associated hemolysis is thought to potentiate rickettsia-induced vasculitis.
Common laboratory findings include elevated creatine kinase, elevated ALT and AST, elevated LDH, hypoalbuminemia, hyponatremia and thrombocytopenia. White blood cell count is usually normal. The best diagnostic test is an indirect immunofluorescence antibody assay. A single titer of 128 or higher can be consistent with recent infection. Titers of 16 to 64 can be seen in recent or past infection. A fourfold increase in antibody titer between acute and convalescent specimens collected 2 to 4 weeks apart is consistent with recent infection
Treatment with doxycycline decreases the average length of febrile illness from approximately 2 weeks to less than 4 days. Treatment 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.
Specimen requirement is serum. Blood should be collected in a red top tube.
Reference
Stern RM et al. A headache of a diagnosis. N Engl J Med 2018;379:475-79.
