OPHEPR; Typhus Fever - Profile for Healthcare Workers

Causative Agent: Typhus fever is a rickettsial disease caused by the organism Rickettsia prowazekii, a Gram negative, obligate intracellular bacterium.

Routes of Exposure: Humans are exposed to epidemic typhus through arthropod vectors, primarily the human body louse.

Infective Dose & Infectivity: The infective dose is unknown. All people are considered susceptible, though older adults may be more severely affected.

Incubation Period: The incubation period ranges from 1 to 2 weeks, but is usually 12 days.

Clinical Effects: Illness usually starts suddenly with headache, chills, prostration, fever, and generalized body aches. A macular eruption appears in four to seven days, initially on the upper trunk, followed by spread to the entire body, but usually not to the face, palms, or soles. The rash starts as maculopapular, becomes petechial or hemorrhagic, then develops into brownish-pigmented areas. The rash may be more concentrated in the axillae. Changes in mental status are common with delirium or coma. Toxemia is usually pronounced. Myocardial and renal failure can occur when the disease is severe. When untreated, the fever and illness last for 2 weeks.

Lethality: The death rate for untreated epidemic typhus increases with age and varies from 10% to 40%.

Transmissibility: Typhus fever is transmitted from person to person by the body louse, which feeds on the blood of humans. Infected lice excrete rickettsiae in their feces and usually defecate at the time of feeding. People are infected when they rub feces or crush lice in the bite, superficial abrasions, or mucous membranes. Inhalation of infective louse feces in dust may account for some infections. Transmission has also been associated with contact with infected flying squirrels in the United States, their nests, or their ectoparasites.

Primary contaminations & Methods of Dissemination: As a bioterrorism weapon, R. prowazekii would most likely be delivered via aerosolization.

Secondary Contamination & Persistence of organism: Direct person-to-person spread of the disease does not occur in the absence of the vector. Rickettsia can remain viable in a dead louse for weeks.

Decontamination & Isolation:

Patients – Standard precautions should be practiced with patients with typhus. Louse-infected people should be treated with pediculocides containing pyrethrins (0.16-33%), piperonyl butoxide (2-4%), crotamiton (10%), or lindane (1%). Several applications may be needed because lice eggs are resistant to most insecticides.
Equipment, clothing & other objects: Washing clothes in hot water kills lice and eggs. Insecticides dusted onto clothing has been effective in epidemics.

Laboratory testing: Culture isolation of R. prowazekii is rarely attempted. The preferred serology for acute and convalescent antibodies is the IFA test, although ELISA, microagglutination and latex agglutination are also available. Antibody tests usually become positive in the second week. Rickettsiae an be detected in tissue biopsies by PCR or immunohistochemical assays.

Therapeutic Treatment: Doxycycline is the treatment of choice for epidemic louseborne typhus fever. Therapy should be administered until the patient is afebrile for at least 3 days and clinical improvement is documented; the usual duration of therapy is 7 to 10 days. Severe disease can require a longer course of treatment.

Despite concerns regarding dental staining after use of a tetracycline-class antimicrobial agent in children 8 years of age or younger, doxycycline provides superior therapy for this potentially life-threatening disease. In people who are intolerant of tetracyclines, intravenous chloramphenicol or fluoroquinolones can be considered. Fluoroquinolones are not recommended for people younger than 18 years of age. When faced with a seriously ill patient with possible typhus, suitable therapy should be started without waiting for laboratory confirmation.

Prophylactic Treatment: Vaccine is no longer available in the United States and post-exposure chemoprophylaxis is not indicated. Apply residual insecticide to those who are subject to risk.

Differential Diagnosis: The differential diagnoses should includes febrile illnesses such as anthrax, dengue fever, infectious mononucleosis, leptospirosis, malaria, meningitis, meningococcemia, relapsing fever, Rocky Mountain spotted fever, syphilis, toxic shock syndrome, tularemia, typhoid fever, rubella, measles, and other rickettsial diseases.

References:

Chin J. Control of Communicable Diseases Manual, Seventeenth Edition, American Public Health Association; 2000.
American Academy of Pediatrics. Epidemic Typhus. In: Pickering LK, ed. Red Book: 2003 Report of the Committee on Infectious Diseases. Elk Grove Village, IL: American Academy of Pediatrics; 2003: 669-670.
Center for Food Security and Public Health. Typhus Fever – Rickettsia prowazekii, Iowa State University College of Veterinary Medicine

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