Typhus, Endemic (Murine)

Rickettsia typhi, a ubiquitous pathogen recognized on all continents, is transmitted from rat to rat through the rat flea

Humans usually acquire the infection in an urban or suburban setting when bitten by an infected flea

Onset is gradual (resembling recrudescent epidemic typhus)

Symptoms of endemic typhus are less severe symptoms and have a shorter duration of illness than epidemic typhus (7–10 days versus 14–21 days)

Endemic typhus is usually self-limited

Rare human cases in the developed world occur in travelers, usually to Southeast Asia, Africa, or the Mediterranean area, although other pockets of infection are also known to occur in the Andes and the Yucatán

In the United States, cases are mainly reported from Texas and Southern California

Fever, headache, myalgia, and chills

Relative bradycardia is reported

Maculopapular rash occurs in around 50% of cases; it is concentrated on the trunk, mostly sparing the palms and soles, and fades rapidly

Anemia, thrombocytopenia, leukopenia, hyponatremia, and elevated levels of liver enzymes commonly occur

If illness is acquired during early pregnancy, it may be associated with

• Maternal death

• Miscarriage

• Preterm birth

• Low birth weight

Differential diagnosis: Rocky Mountain spotted fever

Complications

• Pneumonia (most common), pleural effusion, and respiratory failure

• Neurologic (peripheral facial paralysis, meningismus, ataxia, seizures)

• Acute kidney injury

• Multiorgan failure

• Ocular findings, disseminated intravascular coagulation, and hemophagocytosis syndrome are rare

Serologic confirmation may be necessary for differentiation, with complement-fixing or immunofluorescent antibodies detectable within 15 days after onset, with specific R typhi antigens

A fourfold rise in serum antibody titers between the acute and the convalescent phase is diagnostic

R typhi antigens frequently cross-react with those of R prowazekii

During the first week of illness, polymerase chain reaction is the most sensitive test if samples are taken before doxycycline administration

Doxycycline

• Dosage: 100 mg orally twice daily for 7–10 days (or until the patient is afebrile for 48 hours)

• Drug of choice, except during pregnancy

Ciprofloxacin (500–750 mg orally twice a day) and ampicillin (500 mg orally three times a day) are reportedly successful in pregnant women

Azithromycin is frequently used but is likely inferior to doxycycline and is not associated with improved fetal outcomes