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Typhus - Causes
Last reviewed: 04.07.2025
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Causes of typhus
The cause of typhus is Rickettsia prowazekii, a polymorphic gram-negative microorganism ranging in size from 0.5 to 1 µm, an obligate intracellular parasite.
Rickettsia prowaczekii is cultivated on chicken embryos, in tissue culture and from mouse lungs. Rickettsia quickly perish in a humid environment, but in a dried state they remain viable for a long time (in lice feces - more than 3 months), tolerate low temperatures well, are sensitive to disinfectants [НСНО-methanal (formaldehyde), sodium benzenesulfochloramide (chloramine B), phenol, acids, alkalis, etc.] in concentrations usually used for disinfection.
The causative agent of epidemic typhus contains a heat-labile toxin of protein nature.
Rickettsia prowacekii is sensitive to tetracyclines, chloramphenicol (levomycetin), rifampicin and drugs of the fluoroquinolone group.
[ Epidemiology of typhus
Typhus is an anthroponosis. The source and reservoir of infection is a person with epidemic or relapsing typhus (Brill's disease). The period of infectiousness corresponds to the duration of rickettsiaemia and is approximately 20-21 days: the last 2-3 days of the incubation period, the entire febrile period (16-17 days) and another 2-8 days after the temperature has returned to normal.
The main mechanism of infection is transmission. Rickettsia carriers are lice, mainly body lice (Pediculis humanus carporis), much less often head lice (Pediculis humanus capitis). In the absence of pediculosis, the patient is not dangerous to others.
Rickettsiae penetrate the digestive system of the louse when sucking blood from the patient, multiply in the epithelial cells and after their destruction enter the intestinal lumen and the louse's feces. The louse becomes infectious 5-6 days after sucking blood and remains infectious until it dies from rickettsiosis (approximately 2 weeks). Each time the louse sucks blood, it defecates, and the louse's feces containing a huge amount of rickettsiae get onto the skin. When biting, the louse injects enzymes into the skin that cause itching. A person becomes infected as a result of the penetration of rickettsiae through skin lesions (abrasions, scratches) due to rubbing in louse feces and intestinal particles of crushed infected parasites.
Lice are sensitive to temperature and quickly leave the bodies of the dead and sick with high body temperatures, crawling onto healthy people.
In isolated cases, infection can be transmitted by airborne dust when inhaling dried lice feces or when these feces come into contact with the conjunctiva of the eyes. There are known cases of infection by aerosol transmission as a result of inhaling rickettsia-infected dust particles when shaking dirty laundry, as well as by transfusing blood taken from donors in the last days of the incubation period.
A sick person does not excrete Rickettsia Prowaczekii with any of the secretions. After the disease, a long-term immunity is formed, which may be non-sterile, due to which some of those who have had the disease (up to 10%) may develop a repeated (recurrent) typhus - Brill's disease - after 20-40 years with a decrease in immunity.
Rickettsiae circulating in North America (R. Canada) are cell-borne.
Some epidemiological features of typhus:
- morbidity in the winter-spring period:
- absence of endemic foci:
- the influence of social factors: pediculosis, poor sanitary and hygienic conditions, overcrowding, mass migration, lack of centralized water supply, baths, laundries;
- the occurrence of epidemics during wars and natural disasters;
- the risk of disease in people without a fixed abode, as well as in workers in the service sector: hairdressers, baths, laundries, healthcare facilities, transport, etc.;
- the disease occurs more frequently in men aged 15-30 years.