Transmission
Typhus is transmitted to people through contact with the feces of a flea infected with R. typhi or R. felis. The primary animals known to harbor infected fleas include rats, feral cats, and opossums. People with exposure to animals and their infected fleas are at risk of acquiring flea-borne typhus. Pet dogs and cats that spend time outside may also come in contact with infected fleas and can carry them to humans. Infected animals are not known to get sick from flea-borne typhus. Typhus cannot be transmitted from person-to-person.
Clinical Characteristics
Typhus symptoms typically occur 7 to 14 days after exposure. Typhus presents as a non-specific febrile illness. Symptoms may include headache, chills, myalgia, abdominal pain, and/or vomiting. A rash, typically maculopapular, may appear after 1 week, but may also be absent altogether. Laboratory abnormalities include leukopenia, thrombocytopenia, and elevation of hepatic transaminases. Flea-borne typhus may be a mild, self-limited illness, or can present as severe disease requiring hospitalization. Fatalities occur in less than 1% of cases. Severe cases may result in renal, respiratory, ophthalmologic, cardiac, or neurologic dysfunction. Adults with advanced age or G6PD deficiency are at greatest risk for severe disease.
Diagnosis
A presumptive diagnosis of typhus should be made based on clinical presentation and exposure history. While a history of exposure to fleas or outdoor animals supports the diagnosis, it is important to note that often cases have no known environmental exposures.
The diagnosis should be confirmed with serologic testing for Rickettsia typhi IgG and IgM antibodies. As there can be cross-reactivity with other Rickettsiae, LAC DPH also recommends testing for antibodies against R. rickettsii, the causative agent of Rocky Mountain Spotted Fever.
The indirect immunofluorescence antibody assay is the preferred serologic test as it can provide quantitative results. As serology performed on samples collected within the first week of symptom onset can often be falsely negative, confirmation of R. typhi diagnosis requires a four-fold increase in IgG titers in paired serologic samples. These samples should be collected during the acute stage (in the first two weeks of illness or while the patient is experiencing symptoms) and in the convalescent stage (2 weeks later). However, if the patient does not return for the convalescent sample, a probable typhus diagnosis can be made with a single positive IgG or IgM sample plus supportive clinical data.
Testing is available at many commercial laboratories and is free of charge at the LAC Public Health Laboratory (PHL). For more information on submitting specimens to LAC PHL, see the laboratory testing guidelines on the LAC DPH flea-borne typhus testing webpage.
For more detailed information on testing, consult the “How do you test for flea-borne typhus” section from the Centers for Disease Control and Prevention's flea-borne typhus Clinical FAQs.
Treatment
Treatment decisions should be based on clinical presentation. Treatment should not be delayed pending laboratory confirmation.
Flea-borne typhus is readily treated with antibiotics. Doxycycline is the treatment of choice; the dose of doxycycline for adults is 100 mg orally BID. Treatment should occur for at least 48 hours after the patient becomes afebrile or for seven days, whichever is longer.