Rikketsiozı

Rickettsioses - a group of acute transmissible infectious diseases caused by rickettsia 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's disease, bacillary angiomatosis, bacillary purple hepatitis) and ehrlichiosis (fever sennetsu, monocytic and granulocytic ehrlichiosis).

Epidemiology of rickettsiosis

All rickettsial diseases are divided into anthroponoses (typhus, recurrent typhus) and natural focal zoonoses (other infections caused by rickettsiae). 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.

[1], [2]

What causes rickettsiosis?

Rickettsial disease caused by the genera Rickettsia and Coxiella family Rickettsiaceae - Gram-negative bacteria, obligate intracellular parasites, do not grow on nutrient media. For their cultivation using chicken embryos; and their fibroblasts, mammalian cell cultures. They have a pronounced pleomorphism: depending on the phase of the infectious process, they can be coccoid or short rod-shaped. The nucleus is absent: the nuclear structure is represented by grains containing DNA and RNA. Rickettsia poorly perceive the main aniline dyes, so usually for their color using the method of Romanovsky-Giemsa. Bacteria contain thermolabile 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 heat and the effects of disinfectants (with the exception of Burnet's coxiels), but they remain in a dried state and at low temperatures for a long time. Sensitive to antibiotics of the tetracycline group, fluoroquinolones.

Pathogenesis of rickettsiosis

Penetrating through the skin, rickettsia multiply in the place 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 (rash on the skin, damage to the heart, membranes and substances of the brain with the formation of infectious toxic syndrome).

[3], [4], [5], [6]

Symptoms of rickettsiosis

In most modern classifications, there are three groups of rickettsios.

• Group of typhus:
  • epidemic typhus and its recurring form - Brill's disease (anthroponosis, pathogen - Rickettsia prowazekii Rocha-Lima, carriers - lice);
  • epidemic (rat) typhus (pathogen Rickettsia mooseri, pathogen reservoir - rats and mice, carriers - fleas);
  • zutsugamushi fever, or Japanese river fever (pathogen - Rickettsia tsutsugamuchi, reservoir - rodents and ticks, carriers - ticks).
• Group of spotted fevers:
  • Rocky Mountains spotted fever (pathogen - Rickettsia rickettsii, reservoir - animals and birds, carriers - 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 North Asia (pathogen - Rickettsia sibirica, reservoir - rodents and ticks, carriers - ticks);
  • vesicular, or smallpox, rickettsiosis (pathogen - Rickettsia acari, reservoir - mice, carriers - mites).
• Other rickettsioses: Q fever (pathogen - Coxiella burneti, reservoir - many species of wild and domestic animals, ticks, carriers - ticks).

[7],

Diagnosis of rickettsiosis

[8], [9], [10]

Clinical diagnosis of rickettsiosis

All human rickettsioses are acutely occurring cyclic diseases (with the exception of Q fever, which is possible for a chronic course) with severe intoxication, characteristic symptoms of vascular and CNS lesions, typical exanthema (except Q fever). Each rickettsiosis is characterized by a certain clinical picture. So, symptoms of tick-borne rickettsiosis occur on the 6-10th day after the tick bite and include the occurrence of primary affect at the site of tick suction, which is a typical inoculation scab (“tache noir”), and regional lymphadenitis.

Laboratory diagnosis of rickettsiosis

Laboratory diagnosis of rickettsiosis is the identification of the pathogen and specific antibodies.

Isolation of the pathogen is an absolute diagnostic criterion. Rickettsia is grown on cell tissue culture. They are isolated mainly from blood, biopsy specimens (preferably from the area of inoculation scab) or tick biomass. Working with rickettsiae is allowed only in specially equipped laboratories with a high degree of protection, therefore, the isolation of the pathogen is rarely carried out (usually - for scientific purposes).

Diagnose rickettsioses using serological methods: RIGA, RAC with rickettsial antigens, RIF and RNIF, which allows to determine IgM and IgG separately. Microimmunofluorescence is considered the reference method. The widespread use of ELISA, which is used to identify the pathogen, to determine its antigens and specific antibodies.

So far, Weil-Felix RA is used, based on the fact that the serum of patients with rickettsiosis is able to agglutinate strains OX, OX2, and OX3, Proteus vulgaris.

[11], [12]

Treatment of rickettsiosis

Treatment of rickettsiosis 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 in a dose of 2 g / day in four doses. Antibiotic treatment is carried out until the 2-3rd day after the temperature normalizes.

How to prevent rickettsioses?

Prevention of rickettsiosis: vector control (for example, lice with typhus), pest control using modern effective insecticides, the use of repellents, protective suits (when attacked by ticks).

It is forbidden to eat milk and meat of sick and involuntarily slaughtered animals. When a tick attacks or people stay in an endemic focus, it is recommended to use doxycycline and azithromycin for emergency prophylaxis. With some rickettsiosis (typhus, Q fever), active immunization is carried out.

What is the prognosis for rickettsioses?

With timely, full-fledged etiotropic treatment in the vast majority of cases, complete recovery occurs. With malignant rickettsiosis, for example, with lousy (epidemic) typhus, spotty fever of the Rocky Mountains and tsutsugamushi fever in the absence of specific treatment (antibacterial therapy) in 5-20% of cases death occurs. With Q fever, the process may be chronized.