Coxiella burnetii

Coxiella burnetii is a tiny gram-negative cocobacillus, 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 cocobacillus
 * 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  lungs
 * antibodies against the first phase causes  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 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 incubation period 20 days, which is called Q-fever ( query  = question, because at first etiology was uncertain), it is 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
 * chronic form is culture negative endocarditis

Treatment

 * 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