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Rickettsioses
Last reviewed: 05.07.2025
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Rickettsioses are a group of acute transmissible infectious diseases caused by rickettsiae and characterized by the development of generalized vasculitis, intoxication, damage to the central nervous system, and specific skin rashes. This group does not include bartonellosis (benign lymphoreticulosis, Carrion disease, bacillary angiomatosis, bacillary purple hepatitis) and ehrlichiosis (sennetsu fever, monocytic and granulocytic ehrlichiosis).
Epidemiology of rickettsioses
All rickettsial diseases are divided into anthroponoses (typhus, relapsing typhus) and natural focal zoonoses (other infections caused by rickettsia). In the latter case, the source of infection is small rodents, cattle and other animals, and the carrier is blood-sucking arthropods (ticks, fleas and lice).
Rickettsioses are widespread diseases, registered on all continents. In developing countries they account for 15-25% of all febrile diseases of unknown etiology.
What causes rickettsiosis?
Rickettsioses are caused by representatives of the genera Rickettsia and Coxiella of the Rickettsiaceae family - gram-negative bacteria, obligate intracellular parasites that do not grow on nutrient media. Chicken embryos and their fibroblasts, mammalian cell cultures are used for their cultivation. They have pronounced pleomorphism: depending on the phase of the infectious process, they can have a coccoid or short rod-shaped form. The nucleus is absent: the nuclear structure is represented by grains containing DNA and RNA. Rickettsiae poorly perceive basic aniline dyes, therefore the Romanovsky-Giemsa method is usually used for their staining. Bacteria contain heat-labile protein toxins and LPS - a group-specific antigen with endotoxin properties, similar to the antigen of Proteus vulgaris strains. Rickettsiae have hemolytic activity, are unstable in the environment, are sensitive to heating and the effects of disinfectants (except for Coxiella burnetii), but in a dried state and at low temperatures they are preserved for a long time. They are sensitive to antibiotics of the tetracycline and fluoroquinolone groups.
Pathogenesis of rickettsiosis
Penetrating through the skin, rickettsia multiply at the site of introduction. In some rickettsiosis, a local inflammatory reaction occurs with the formation of a primary affect. Then, hematogenous dissemination of the pathogen occurs, as a result of which generalized warty vasculitis develops (skin rashes, damage to the heart, membranes and brain matter with the formation of an infectious-toxic syndrome).
Symptoms of Rickettsial Diseases
Most modern classifications distinguish three groups of rickettsiosis.
- Typhus group:
- epidemic typhus and its relapsing form - Brill's disease (anthroponosis, pathogen - Rickettsia prowazekii Rocha-Lima, carriers - lice);
- epidemic (rat) typhus (pathogen Rickettsia mooseri, reservoir of the pathogen - rats and mice, carriers - fleas);
- Tsutsugamushi fever, or Japanese river fever (pathogen - Rickettsia tsutsugamuchi, reservoir - rodents and ticks, carriers - ticks).
- Spotted fever group:
- Rocky Mountain spotted fever (pathogen - Rickettsia rickettsii, reservoir - animals and birds, vectors - ticks);
- Marseilles, or Mediterranean, fever (pathogen - Rickettsia conori, reservoir - ticks and dogs, carriers - ticks);
- Australian tick-borne rickettsiosis, or North Australian tick-borne typhus (pathogen - Rickettsia australis, reservoir - small animals, carriers - ticks);
- tick-borne typhus of Northern Asia (pathogen - Rickettsia sibirica, reservoir - rodents and ticks, carriers - ticks);
- vesicular, or smallpox-like, rickettsiosis (pathogen - Rickettsia acari, reservoir - mice, carriers - ticks).
- Other rickettsiosis: Q fever (pathogen - Coxiella burneti, reservoir - many species of wild and domestic animals, ticks, vectors - ticks).
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Diagnostics of rickettsiosis
Clinical diagnostics of rickettsiosis
All human rickettsiosis are acute cyclic diseases (except for Q fever, which can become chronic) with severe intoxication, characteristic symptoms of vascular and CNS damage, and typical exanthema (except for Q fever). Each rickettsiosis has a specific clinical picture. Thus, symptoms of tick-borne rickettsiosis appear on the 6th to 10th day after the tick bite and include the appearance of a primary affect at the site of the tick bite, which is a typical inoculation scab ("tache noir"), and regional lymphadenitis.
Laboratory diagnostics of rickettsiosis
Laboratory diagnostics of rickettsiosis involves identifying the pathogen and specific antibodies.
Isolation of the pathogen is an absolute diagnostic criterion. Rickettsiae are grown on cell cultures of tissues. They are isolated mainly from blood, biopsy samples (preferably from the area of the inoculation scab) or tick biomass. Work with rickettsiae is allowed only in specially equipped laboratories with a high degree of protection, therefore isolation of the pathogen is rarely carried out (usually for scientific purposes).
Rickettsioses are diagnosed using serological methods: RIGA, RSK with rickettsial antigens, RIF and RNIF, which allows for the separate determination of IgM and IgG. Microimmunofluorescence is considered a reference method. ELISA has become widely used, which is used to identify the pathogen, determine its antigens and specific antibodies.
To date, the Weil-Felix agglutination method has been used, based on the fact that the blood serum of patients with rickettsiosis is capable of agglutinating strains of OX, OX2, and OX3, Proteus vulgaris.
What tests are needed?
Treatment of rickettsiosis
Treatment of rickettsioses is based on the use of etiotropic therapy. The drugs of choice are tetracycline (1.2-2 g/day in four doses) and doxycycline (0.1-0.2 g/day once). It is possible to use chloramphenicol at a dose of 2 g/day in four doses. Antibiotic therapy is carried out until the 2nd-3rd day after the temperature has returned to normal.
How to prevent rickettsiosis?
Prevention of rickettsiosis: control of carriers (for example, lice in typhus), disinfestation using modern effective insecticides, use of repellents, protective suits (in case of tick attacks).
It is prohibited to consume milk and meat from sick and forcedly slaughtered animals. In case of a tick attack or when people are in an endemic focus, doxycycline and azithromycin are recommended for emergency prevention. For some rickettsiosis (typhus, Q fever), active immunization is carried out.
What is the prognosis for rickettsioses?
With timely, complete etiotropic treatment, complete recovery occurs in the vast majority of cases. In malignant rickettsioses, for example, in louse-borne (epidemic) typhus, Rocky Mountain spotted fever and tsutsugamushi fever, in the absence of specific treatment (antibacterial therapy), a fatal outcome occurs in 5-20% of cases. In Q fever, the process may become chronic.