Epidemic typhus is a potentially lethal, febrile illness caused by the obligate intracellular gram-negative bacterium, Rickettsia prowazekii.
- Typhus is transmitted by infected lice.
- Infections occur in winter or spring.
- Overcrowded conditions:
- Reported in army camps, refugee camps, prisons, and homeless shelters
- Sometimes called “jail fever”
- Poor hygiene:
- Civil strife
- War zones
- Extreme poverty
- In the US:
- Cases often associated with exposure to flying squirrels
- Epidemic typhus outbreaks have been reported in the following countries:
- Central America
- South America
- Eastern Europe
- Northern India
Etiology and Pathophysiology
- Causative agent: R. prowazekii is the most pathogenic member of the Rickettsia genus.
- Human body louse, Pediculus humanus corporis
- Human head louse, P. humanus capitis
- Flying squirrels
- Infected lice pass infectious feces when they feed.
- The feces and not the bite of the louse spread illness in humans.
- Transmitted when the infectious feces of lice or crushed, infected body lice are rubbed into small cuts or abrasions on the skin
- The disease may also be spread when:
- A person breathes in dust containing infected dried feces of lice
- Mucous membranes, such as the conjunctiva of the eye, are exposed to infectious feces
- After entering the body, Rickettsia infect and multiply in the endothelial cells of the small venous, arterial, and capillary vessels.
- Infected endothelial cells enlarge due to microbial proliferation.
- Multiorgan vasculitis develops.
- Vasculitis can lead to:
- Thrombosis of the supplying blood vessels: gangrene of the distal parts of the extremities, nose, ear lobes, and genitalia
- Deposition of leukocytes, macrophages, and platelets results in the formation of small nodules.
- Increased vascular permeability:
- Loss of intravascular colloid with subsequent hypovolemia
- Loss of electrolytes
- Decreased tissue perfusion → organ failure
- Incubation period: usually < 14 days
- Clinical manifestations:
- Severe headache
- Rash (a pink macular rash that spares the palms and soles)
- Nonproductive cough
- Abdominal pain
- Severe epidemic typhus can lead to:
- Loss of digits, limbs, or other appendages
- CNS dysfunction (ranging from decreased mentation to coma)
- Multiorgan system failure
- Brill-Zinsser disease:
- Recrudescence of epidemic typhus following an initial attack
- Patients can have a prolonged, asymptomatic R. prowazekii infection for years.
- A relapse that occurs months or years following the 1st illness, when the immune system is weakened due to certain medications, advanced age, or illness
- Symptoms are similar to the original infection, but usually milder.
Diagnosis and Management
- Epidemic typhus is diagnosed by its clinical features in the setting of a louse infection.
- Confirmatory laboratory tests:
- Biopsy of rash using fluorescent antibody staining to determine the causative microbe
- Acute and convalescent serologic testing
- Primary treatment: doxycycline (4 mg/kg/day)
- Alternative treatments:
- Tetracycline (25–50 mg/kg/day)
- Chloramphenicol 500 mg orally or IV 4 times daily for 7 days
- Louse control:
- Lice may be eliminated by dusting infested individuals with malathion or lindane.
- Washing of clothing in hot water
- Sweeping off dust particles, as they contain excreta of infected lice
- Immunization is highly effective for prevention; however, typhus vaccines are no longer available in the US.
- Antibiotic prophylaxis with doxycycline (once weekly) for individuals traveling to high-risk areas
- Mortality rate of untreated epidemic typhus:
- 20% in otherwise healthy individuals
- 60% in the elderly or in debilitated individuals
- When treated with appropriate antibiotics, the mortality rate can decrease to approximately 3%–4%.
- Rocky Mountain spotted fever (RMSF): a disease caused by R. rickettsii and transmitted by ixodid ticks. The incidence is highest in children < 15 years and in individuals who frequent tick-infested areas for work or recreation. Rocky Mountain spotted fever presents with abrupt headaches, chills, prostration, muscular pains, and centripetal rash, and is diagnosed based on clinical features, serology, and PCR. Treatment is using doxycycline.
- Kawasaki disease: an acute febrile illness of early childhood of unknown cause. Kawasaki disease is the leading cause of acquired coronary artery disease in developed nations and is characterized by vasculitis of the medium-sized arteries, especially coronary arteries. Other features of Kawasaki disease include rashes on the extremities, oropharyngeal rash, and bulbar conjunctivitis, as well as acute, unilateral, nonpurulent cervical lymphadenopathy. The diagnosis is made on clinical grounds and the diagnostic test of choice is echocardiography. The mainstays of treatment are aspirin and IV Igs.
- Anthrax: a disease caused by the gram-positive microbe Bacillus anthracis. Anthrax is transmitted to humans when they come in contact with infected animals or their products. Cutaneous anthrax begins as a painless, pruritic, red-brown papule 1–10 days after exposure to infective spores. The papule can enlarge, become necrotic, and form a black eschar. The diagnosis is made through clinical findings and is based on occupational and exposure history. Confirmatory laboratory tests include Gram staining and culture, direct fluorescent antibody test, and PCR. Empiric treatment is using ciprofloxacin, levofloxacin, moxifloxacin, or doxycycline.
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