burnetii

Burnetii, in taxonomic use, refers to Coxiella burnetii, a Gram-negative, obligate intracellular bacterium and the causative agent of Q fever in humans. It belongs to the Gammaproteobacteria and exhibits a developmental cycle that alternates between a metabolically active large cell variant and a highly resistant small cell variant adapted for environmental survival.

Ecology and transmission: Coxiella burnetii is found in a wide range of livestock, including cattle, sheep, and goats, often persisting in animal products and birth materials. Humans are primarily exposed through inhalation of aerosols from contaminated births, placentas, feces, or dust. Tick vectors can play a role in animal maintenance, but they are not the main route of human transmission. Ingestion of unpasteurized dairy products has been reported but is less common.

Clinical features: Acute Q fever typically presents with fever, severe headache, malaise, and myalgia, and may progress to pneumonia or hepatitis. The incubation period is about 2 to 3 weeks. Chronic Q fever, most often presenting as endocarditis, occurs in individuals with preexisting valvular disease or immunosuppression and can be difficult to diagnose due to nonspecific symptoms.

Diagnosis and treatment: Acute infection is usually treated with doxycycline for about 14 days. Chronic Q fever requires longer therapy, typically doxycycline in combination with hydroxychloroquine for 18–24 months. Diagnosis relies on serology distinguishing phase I and phase II antibodies and, when needed, PCR for bacterial DNA. Culture is hazardous and rarely performed.

Genome and prevention: The genome is approximately 2.0–2.5 megabases, with extensive repetitive elements reflecting its intracellular lifestyle. Prevention includes vaccination for at-risk populations (such as the Q-VAX vaccine in Australia) and adherence to biosafety guidelines for handling suspected cases and cultures.