Q FEVER : CLINICAL ASPECTS
C. burnetii has an affinity for the reticuloendothelial system, but little is known of the pathology, because fatal cases are rare. As in livestock, most human infections are inapparent. When clinically evident, Q fever usually begins 9 to 20 days after inhalation, with abrupt onset of fever, chills, and headache. A mild, dry, hacking cough and patchy interstitial pneumonia may or may not be present. There is no rash. Hepatosplenomegaly and abnormal liver function tests are common.
Complications such as myocarditis, pericarditis, and encephalitis are rare. Chronic infection is also rare but particularly important when it takes the form of endocarditis. There is evidence that the strains associated with endocarditis constitute an antigenic subgroup of C. burnetii.
Diagnosis is usually made by demonstrating high or rising titers of antibody to Q fever antigen by complement fixation, IFA, or enzyme immunoassay procedures. Although most infections resolve spontaneously, tetracycline therapy is believed to shorten the duration of fever and reduce the risk of chronic infection. Vaccines have been shown to stimulate antibodies, and some studies have suggested a protective effect for heavily exposed workers.shown to stimulate antibodies, and some studies have suggested a protective effect for heavily exposed workers.
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