Rickettsia prowazeki is a small obligately intracellular Gram-negative bacterium measuring approximately 0.4 μm x 1.5 μm.
The great epidemics of typhus that plagued humans since ancient times ceased shortly after the Second World War with the widespread application of insect control procedures and other hygienic measures. Endemic foci exist in certain regions where louse infestation is common, including parts of Mexico, central and South America, central and east Africa and various regions of Asia. Epidemics may reappear during times of war or famine.
Reservoirs: Humans, flying squirrels (United States only).
Vectors: Transmitted from person to person by lice; fleas may play a role in transmission of flying-squirrel-associated typhus.
Mode of transmission
The disease is transmitted particularly by the body louse Pediculus humanus corporis. Infection of humans occurs by contact of mucousmembranes or abraded skin with the faeces of lice or fleas that havebitten a person with acute typhus fever. Infection probably also occursby inhalation of dust contaminated with infected insect faeces or bodyparts. Patients are infective for lice during the febrile phase of thedisease and perhaps for 2–3 days afterwards. Direct person-to-persontransmission does not occur.
Incubation period: The incubation period is usually 1–2 weeks.
The disease has a variable onset, often sudden, with chills, body aches, fever, headache and weakness. During the first week a macular rash appears, initially on the upper trunk, and then spreads. The symptoms grow progressively more severe, with the critical period in the second or third week. Stupor and coma may be interrupted by attacks of delirium. Recovery is marked by abrupt cessation of fever, usually in the second febrile week, but, if untreated, mortality ranges from 10% to 40%, increasing with age. The disease may reappear years after the initial infection, usually in a milder form known as Brill-Zinsser disease.
Specific antibodies appear about 2 weeks after infection, when diagnosis may be obtained by immunofluorescent antibody test. More rapid diagnosis may be obtained by immunohistological demonstration of the organism or by PCR, using blood collected during the acute phase of the disease. Biosafety Level 2 practices, equipment and facilities are recommended for activities not involving propagation of the pathogen, such as microscopic and serological examinations. Biosafety Level 3 is recommended for activities involving the handling of infected human or animal tissues.
Medical management and public health measures
Isolation of patients is not necessary. If lice are present, insecticide should be applied to clothing, bedding, living quarters and patient contacts in order to prevent spread of the disease. Louse-infested individuals likely to have been exposed to typhus fever should be deloused and placed under quarantine for 15 days after insecticide application and close patient contacts should be kept under fever watch for 2 weeks. Reapplication of insecticide may be needed as previously laid eggs hatch.
Prophylaxis and treatment
Antimicrobials including doxycycline are effective in prophylaxis and treatment and should be given if typhus is suspected.