Dr  Sampurna Roy  MD

Q fever is caused by Coxiella burnetii , which is a rickettsia , that is distributed globally. It differs from rickettsia, by not involving capillary blood vessels, like other rickettsia. It is intracellular in macrophages and highly resistant to drying.

Mode of Infection:

The organism passes from the tick host to cattle, sheep, goat etc. Aerosol droplets spread the infection from person to person.

i) Most commonly, air borne by breathing air contaminated by drying animal placentas or other products of birth.

ii) By coming in contact with infected soil or wool.

ii) Less commonly, by ingestion of contaminated milk.

iii) Rarely by tick bite.

iv) It occurs in laboratory workers, handling meat, skin, milk, wool & fertilizer.

 Incubation period:  Normally 9-18 days.

 Clinical features:

1. Asymptomatic- Seropositive cases. 

Pregnancy may activate infection with involvement of placenta causing abortion. Placenta & abortus contain organisms.

2. Symptomatic cases:

a) Acute Q fever :  Starts with influenza -like fever followed by myalgia , headache , sweating.  It is usually self limited & rarely fatal. Nonspecific fever with atypical pneumonia, rarely followed by hepatospenomegaly.

b) Chronic Q fever:  Chronic Q fever may start 2-20 years after infection.

Chronic infective endocarditis with vegetation is the main complication of the chronic form of Q fever.  Coxiella Burnetii endocarditis is very rare. Rickettsiae are seen as extracellular colonies in the vegetations on the valve.   Image Link

Blood cultures are negative and diagnosis is essentially based on indirect immunofluorescence serum analysis.

It may be associated with involvement of liver.

Glomerulonephritis occurs in some patients with chronic Q fever endocarditis.

Pathology:

(i) Bronchopneumonia  with interstitial pneumonitis.

(ii) Exudate contains macrophage, lymphocytes, RBC & neutrophils.

(iii) Alveolar septa are thickened with mononuclear cell infiltrate.

(iv) Intracellular organisms in monocytes are present.

(v) Granulomas may be present in liver, spleen & bone marrow.

Granulomas contain central vacuolar space- “doughnut/ring granuloma”. Such granulomas are typical of Q fever, caused by the rickettsial bacterium C. burnetii. There is a central empty  space (that contains immunoglobulins reactive to C. burnetii , epithelioid cells & a fibrin mesh between & outside epithelioid cells.

This pattern is not typical of other common marrow infections such as   tuberculosis and brucellosis .

In Q fever granulomas are present in the liver:  D/D:  Granulomas are also seen in lymphoma, allopurinol drug effect, toxoplasmosis , Epstein-Barr Virus infection  & CMV infection, leishmaniasis, Hepatitis A  and  staphylococcal   septicaemia .

In Q fever granulomas are present in the marrow:  D/D: Granulomas are also seen in Tuberculosis, brucellosis , leishmaniasis , histoplasmosis , Hodgkin's disease , sarcoidosis .