Coxiella burnetii

Coxiella burnetii is a tiny gram-negative coccobacillus, staining well according to Giemsa. C. burnetii is the only species of the genus Coxiella and is the causative agent of Q-fever. Due to its low infectious dose and good resistance to drying, Coxiella can be used as a biological weapon.

Morphology

 * highly pleiomorphic, small coccobacillus
 * the wall is formed similarly to G minus bacteria

Physiology

 * intracellular parasites, multiplying only in the phagolysosome of living cells
 * multiplies in cells, during the cycle large and small forms alternate and at the same time spore-like formations are formed, which, however, differ in their structure from spores of gram-positive bacteria (described by Czechoslovak authors)

Cultivation

 * multiplies at low pH phagolysosome of cells
 * grows on common media and yolk sac of chicken embryos
 * we prove it by special staining in infected cells

Laboratory diagnostics

 * isolation is very dangerous for laboratory workers, and therefore it is performed only in specialized workplaces (VÚ SAV Bratislava, rickettsia department)
 * usually, the diagnosis of Q-fever is performed serologically (immunofluorescence, binding Complement, PCR)

Antigens and toxicity

 * occurrence in a single antigenic type, but there are alternating two phases:
 * Phase I - virulent strains after fresh isolation
 * II. phase - loss of surface polysaccharides during repeated cultures

Pathogenesis

 * the infectious dose is very low, a single cell is enough
 * the first infected cell is mostly alveolar macrophages after its decay blood get Coxielly into many organs, and therefore the disease does not only occur in the lungs
 * antibodies against the first phase cause Coxiell to disappear from the bloodstream
 * cellular immunity is necessary for healing, it fails in a few percent of the infected and the infection then becomes chronic

Epidemiology

 * in nature, the source of the infection are various animals (cattle, goats, sheep, ticks), which excrete Coxielly milk, urine, faeces
 * the largest amount of Coxiell  is found in placentas
 * transmission is most often carried out by inhalation of contaminated dust, less often when ingested or processed contaminated products, very rarely transmission by a tick is possible.

Disease

 * in about half of the cases, the infection is inapparent, therefore the number of registered diseases is not high
 * in other cases it causes an acute infection with an incubation period of 20 days, which is called Q-fever (query = question, because at first etiology was uncertain), it is a typical occupational zoonosis
 * Q fever is manifested as a disease similar to influenza, atypical pneumonia (without cough and no expectoration), very rarely as granulomatous hepatitis, splenomegaly
 * the chronic form is culture-negative endocarditis

Treatment

 * the acute form of Q fever is treated with doxycycline or macrolides
 * the chronic form must be treated for at least 18 months with a combination of doxycycline and hydrochloroquine (basifies the content of lysosomes)

Related articles

 * Gram stain
 * Q fever