Infectious Disease Online
Pathology of Q fever (Coxiella Burnetii )
Q fever is caused by Coxiella
which is a rickettsia,
that is distributed
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.
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.
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.
(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.
In Q fever granulomas are present in the liver:
Differential diagnosis: Granulomas are also seen in lymphoma, allopurinol drug effect, toxoplasmosis , Epstein-Barr Virus infection and CMV infection, leishmaniasis, Hepatitis A and staphylococcal septicaemia.
In Q fever granulomas are present in the marrow:
Survey of laboratory animal technicians in the United States for Coxiella burnetii antibodies and exploration of risk factors for exposure.
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