Clinical Manifestations and Pathology

Subclinical infection is common. Only 191 of 415 newly infected persons were symptomatic in an outbreak in Switzerland in 1983, caused when infected sheep were driven from mountain pastures through several villages on the way to market. The clinical features of acute Q fever are shared by several other infectious agents, and diagnosis depends upon serologic confirmation. Illness begins 2 to 4 weeks after exposure, with the incubation period possibly varying with the infecting dose. There is sudden onset of fever, sweating, shivering, rigors, malaise, joint and limb pains, very severe frontal headache, retro-orbital pain and photophobia, and a mild nonproductive cough. Rash is uncommon. Untreated fever usually lasts 1 to 2 weeks, but pneumonia may persist for several weeks. Abnormal liver function tests are usual, but jaundice is less common. More than half of patients show "ground glass" infiltration due to pneumonitis on chest X-ray, even though severe respiratory symptoms are unusual. Rarer complications of acute Q fever are meningoencephalitis, cerebellar ataxia, coma, myocarditis, pericarditis, infiltration of the bone marrow by granulomas leading to bone marrow failure, orchitis, and placentitis. There may be splenomegaly and lymphocytosis.

Liver biopsy reveals small granulomas containing fibrinoid material. In animal models, coxiellae persist for long periods in liver, spleen, and lymph nodes and may multiply in the placenta during pregnancy and so be excreted in vast numbers during parturition. There is some evidence that this may occur also in humans.

Chronic Q fever is usually considered a rare occurrence, particularly, but not exclusively, affecting patients with preexisting aortic or mitral valve malformations or disease and occurring from several months up to many years after acute infection. However, the absence of a history of acute Q fever, preexisting heart valve disease, or exposure to animals and animal products does not exclude the possibility of chronic Q fever. Illness begins as a low-grade fever with night sweats, anemia, joint pains, finger clubbing, heart murmur, and developing heart failure. There is usually hepatosplenomegaly. Coxiellae can be isolated from vegetations on damaged or prosthetic heart valves. Vegetations may embolize. Abnormal liver function tests are usual, and chronic Q fever may sometimes present as chronic liver disease.

Acute Q fever can be treated successfully with tetracyclines, chloramphenicol, and erythromycin, but chronic Q fever is difficult to treat. Prolonged administration of combinations of tetracyclines, ri-fampicin, lincamycin, clindamycin, and cotrimox-azole have been recommended, but eventually heart valve replacement may be unavoidable. Reinfection of prosthetic valves has been described, possibly occurring as a result of persistent extracardiac infection.

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