Coxiellae

The causative agent of Q fever is bacteria of the species Coxiella burnetii, which belong to the class Gammuproleu bacteria, order Legionellales, family Coxiellaceae, genus Coxiella. The causative agent was isolated in 1937 in Australia by F. Burnet and M. Freeman.

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Morphology of Coxiella

Coxiella are short gram-negative coccobacteria, 0.2x0.7 µm in size, pleomorphic. According to Zdrodovsky and Romanovsky-Giemsa, they are stained red.

Cultural properties of Coxiella

Obligate intracellular parasites. Cultivated in cell cultures, yolk sac of chicken embryos, guinea pig organism. In cells, they reproduce in cytoplasmic vacuoles, and can reproduce in phagolysosomes.

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Antigenic structure and pathogenicity of Coxiella

Coxiella are subject to phase variations that differ in morphology and antigen specificity. Coxiella in phase 1 have a structural polysaccharide in the cell membrane, are hydrophilic, have greater immunogenicity, are not absorbed by phagocytes in the absence of antibodies. Coxiella in phase 2 are less virulent, sensitive to phagocytosis. Transition to phase 2 occurs after repeated cultivation in a chicken embryo. In infected cells, coxiella form spore-like forms that are most pathogenic for humans.

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Coxiella resistance

Highly stable in the environment. Resistant to formalin and phenol. Resistance to high temperatures and low pH values, to drying is associated with the ability to form endospore-like forms. They survive for months in water and on objects contaminated with the microbe. They survive for up to 2 years in dried feces.

Immunity

At the onset of the disease, antibodies to phase 2 appear in the blood, and at the height of the disease and in convalescents, antibodies to phase 1 are detected.

Epidemiology of Q fever

The reservoir in nature are cattle and small cattle, horses, rodents, wild birds. The microbe is maintained in nature due to the circulation of the pathogen between animals and birds with the participation of multiple species of ixodid and argas ticks. The anthropoid vector does not play a role in the transmission of the pathogen to humans. In animals, Q fever can be asymptomatic, the pathogen is excreted in large quantities with urine, feces, amniotic fluid, and milk. Humans mainly become infected by inhaling aerosols of urine and feces of infected animals, as well as by drinking milk from infected animals and contaminated water. Contaminated aerosols and dust can infect the conjunctiva. Infection is possible through damaged skin upon contact with contaminated amniotic fluid of animals. Aerosols infected with coxiella emitted into the atmosphere can cause an infectious process at a distance of several kilometers from the source of infection. Therefore, Coxiella burnetii is considered as one of the bioterrorism agents, it is included in group B of bioterrorism agents. Transmission of the disease from person to person has not been noted.

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Symptoms of Q fever

The incubation period is 18-21 days. The disease is accompanied by fever, headache, symptoms of acute respiratory disease, which occurs as atypical pneumonia. Nausea and vomiting may be observed. Patients with pneumonia caused by Coxiella burnetii experience liver damage with the development of hepatosplenic syndrome. Sometimes the disease is accompanied by endocarditis. Mortality is no more than 1%.

Diagnosis of Q fever

Diagnosis of Q fever is carried out using a serological method of research in conjunction with the diagnosis of other atypical pneumonia (chlamydial, legionella and mycoplasmal etiology), using complete serum count (CS), ELISA, and indirect RIF.

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Treatment of Q fever

Treatment of Q fever is carried out with tetracycline and new-line antibiotics and fluoroquinolones.

Prevention of Q fever

Vaccination against Q fever with a live vaccine from the M-44 strain (P.F. Zdrodovsky, V.A. Genig) helps prevent Q fever. It is used for epidemiological indications. Non-specific prevention is limited to sanitary and veterinary measures.