Etiology and Epidemiology

Caused by R. typhi, endemic murine typhus has a rat reservoir and is transmitted by fleas.

• Humans become infected when Rickettsia-laden flea feces are scratched into pruritic bite lesions; less often, the flea bite itself transmits the organisms or aerosolized rickettsiae from flea feces are inhaled.
• In the United States, endemic typhus occurs mainly in southern Texas and southern California; globally, it occurs in warm (often coastal) areas throughout the tropics and subtropics.
• Flea bites often are not recalled by pts, but exposure to animals such as cats, opossums, raccoons, skunks, and rats is reported by ∼40%.
• Risk factors for severe disease include older age, underlying disease, and treatment with a sulfonamide drug.

Clinical Manifestations

Prodromal symptoms 1-3 days before the abrupt onset of chills and fever include headache, myalgia, arthralgia, nausea, and malaise; nausea and vomiting are nearly universal early in illness.

• Rash is apparent at presentation (usually ∼4 days after symptom onset) in 13% of pts; 2 days later, half of the remaining pts develop a maculopapular rash that involves the trunk more than the extremities, is seldom petechial, and rarely involves the face, palms, or soles.
• Pulmonary disease is common, causing a hacking, nonproductive cough in 35% of pts. Almost one-fourth of pts who undergo CXR have pulmonary densities due to interstitial pneumonia, pulmonary edema, and pleural effusions.
• Laboratory abnormalities include anemia, leukopenia early in the course, leukocytosis late in the course, thrombocytopenia, hyponatremia, hypoalbuminemia, mildly increased hepatic aminotransferase levels, and prerenal azotemia.
• Complications may include respiratory failure, hematemesis, cerebral hemorrhage, and hemolysis.
• The duration of untreated disease averages 12 days (range, 9-18 days).

Diagnosis

The diagnosis can be based on culture, PCR, serologic studies of acute- and convalescent-phase sera, or immunohistology, but most pts are treated empirically.

Etiology and Epidemiology

Epidemic typhus is caused by R. prowazekii and is transmitted by the human body louse. Eastern flying squirrels and their lice and fleas maintain R. prowazekii in a zoonotic cycle.

• The louse lives in clothing under poor hygienic conditions, particularly in colder climates and classically at times of war or natural disaster.
• Lice feed on pts with epidemic typhus and then defecate the organism on their subsequent host during their next meal. The pt autoinoculates the organism while scratching.
• Brill-Zinsser disease is a recrudescent form of epidemic typhus whose occurrence years after acute illness suggests that R. prowazekii remains dormant in the host, with reactivation when immunity wanes.

Clinical Manifestations

Epidemic typhus presents abruptly with the onset of high fevers, prostration, severe headache, cough, and severe myalgias. Photophobia with conjunctival injection and eye pain is also common.

• A rash appears on the upper trunk around the fifth day of illness and spreads to involve all body-surface areas except the face, palms, and soles.
• Confusion and coma, skin necrosis, and gangrene of the digits are noted in severe cases.
• Untreated, the disease is fatal in 7-40% of cases. Pts develop renal failure, multiorgan involvement, and prominent neurologic manifestations.

Diagnosis

Epidemic typhus is sometimes misdiagnosed as typhoid fever. The diagnosis can be based on serology, immunohistochemistry, or detection of the organism in a louse found on a pt.