Symptoms: Chronic Q fever usually occurs in patients with previous valvular heart disease, chronic renal insufficiency, or immunosuppression. Chronic Q fever generally implies endocarditis. Fever is generally low grade or absent. The disease should be suspected in all patients with culture-negative endocarditis.
Epidemiology: The primary sources of human infection are infected sheep, cattle, camel and goats. But cats, dogs, rabbits, and pigeons also can transmit C. burnetii to humans and cause Q fever. The wild reservoir includes ticks. In the infected animals C. burnetii localizes to the uterus and the mammary glands and is activated during pregnancy. C. burnetii is concentrated in the placenta and at the time of parturition (delivery), C. burnetii organisms are released into the air, and infection follows inhalation of aerosolized organisms by a susceptible host. So, C. burnetii can be a potential agent of bioterrorism.
Veterinarians, abattoir workers and other individuals who have contact with infected animals, mainly newborn animals or products of conception are at great risk of getting Q fever. C. burnetii is found in milk for weeks to months after parturition and ingestion of contaminated milk in some areas can be a major route of transmission to humans. But the vast majority of Q fever cases result from inhalation of contaminated aerosols.
Q fever can occur throughout the world except
Treatment: The treatment of chronic Q fever is very difficult and needs careful follow-up. Preferred regimen of treatment of chronic Q fever is doxycycline (100 mg twice a day) and hydroxychloroquine (200 mg thrice a day; plasma concentration maintained at 0.8–1.2 µg/ml) for 18 months. This is better than a regimen of doxycycline and ofloxacin. Q fever endocarditis requires determination of the minimal inhibitory concentration (MIC) of doxycycline for the patient’s isolate of C. burnetii and measurement of serum doxycycline levels. The doxycycline-hydroxychloroquine regimen is successful in patient with HIV infection and Q fever endocarditis. If doxycycline-hydroxychloroquine cannot be used, than at least two antibiotics active against C. burnetii like Rifampin (300 mg once daily) combined with doxycycline (100 mg twice daily) or ciprofloxacin (750 mg twice daily) should be used.
Treatment of C. burnetii infected aortic aneurysms is the same as that for Q fever endocarditis but surgical intervention is frequently required.