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Typhus: causes
Last reviewed: 23.04.2024
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Causes of typhus
The cause of typhus is rickettsia Provacek (R. Prowazekii) - a polymorphic gram-negative microorganism measuring 0.5 to 1 μm, an obligate intracellular parasite.
Riquettsia provacheka is cultivated on chick embryos, in tissue culture and in mice. Rickettsia quickly die in a humid environment, but in a dried state they remain viable for a long time (more than 3 months in feces of lice), tolerate low temperatures, are sensitive to disinfectants [NSO-methanal (formalin), benzenesulfochloramid sodium (chloramine B), phenol , acids, alkalis, etc.] in concentrations commonly used for disinfection.
The causative agent of epidemic typhus contains a thermolabile toxin of protein nature.
The Rickettsia provachek is sensitive to tetracyclines, chloramphenicol (levomycetin), rifampicin, and fluoroquinolone group preparations.
[Epidemiology of typhus
Typhus fever is anthropogenous disease. The source and reservoir of infection is a person who has an 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 normalization.
The main mechanism of transmission is transmissible. Rickettsia carriers are lice, predominantly ward (Pediculis humanus carporis), much less often headaches (Pediculis humanus capitis). In the absence of pediculosis the patient is not dangerous looking around.
Rickettsia enter the digestive apparatus of a louse when the patient sucks, multiply in epithelial cells and, after their destruction, enter the lumen of the intestine and the feces of the louse. The louse becomes infectious 5-6 days after the bloodsucking and retains the infectiousness until death from rickettsiosis (approximately about 2 weeks). With each bloodsucking, lice have an act of defecation, the head gets stool with a large number of rickettsias. When bitten, the louse injects into the skin enzymatic substances that cause itching. A person becomes infected as a result of penetration of rickettsia through skin lesions (abrasions, clefts) due to rubbing of feces of lice and particles of the intestinal tube of crushed infected parasites.
Lice are sensitive to the temperature regime and quickly leave the bodies of the dead and diseased with high body temperature, creeping over to healthy people.
In casuistic cases, it is possible to get airborne dust by inhaling dried feces of lice or by contacting these feces with the conjunctiva of the eyes. There are known cases of infection by aerosol by inhalation of dust particles contaminated with rickettsia by shaking dirty laundry, as well as by blood transfusion from donors in the last days of the incubation period.
A sick person does not single out Ricquetsia Procachek with any of the secrets. After the transferred disease, long-term immunity is formed, which can be non-sterile, in connection with which in some patients who have recovered (up to 10%) in 20-40 years with a decrease in immunity, repeated (recurrent) typhus can occur-Brill's disease.
Rickettsia circulating in North America (R. Canada) is transmitted by cells.
Some epidemiological features of typhus:
- incidence in the winter-spring period:
- absence of endemic foci:
- the influence of social factors: pediculosis, poor hygiene, crowding, mass migration, lack of centralized water supply, baths, laundries;
- the emergence of epidemics during wars and natural disasters;
- risk of disease in people without a specific place of residence, as well as in the service sector: hairdressing salons, baths, laundries, health facilities, etc .;
- more frequent occurrence of the disease in men 15-30 years.