Chlamydia psittaci

Chlamydia psittaci is an obligate intracellular bacterium that causes psittacosis, a zoonotic respiratory disease primarily transmitted from birds to humans. Human infections are relatively rare but can be severe, especially in individuals exposed to infected birds such as bird handlers and poultry workers. The bacterium was previously classified as Chlamydophila psittaci.

Clinical Features

C. psittaci is a non-motile, gram-negative coccus with a distinctive biphasic developmental cycle, alternating between an infectious, environmentally resistant elementary body and a metabolically active reticulate body that replicates within host cells.

Transmission mainly occurs via inhalation of aerosols contaminated with droppings, respiratory secretions, or feathers from infected birds, or through direct contact. Psittacosis in humans typically begins with flu-like symptoms including fever, dry cough, chills, headache, and muscle aches, which can progress to severe pneumonia if untreated. Human-to-human transmission is extremely rare.

Diagnosis

Diagnosis is based on clinical suspicion supported by exposure history, along with laboratory confirmation through serology, PCR, or cell culture. Due to its intracellular lifestyle, C. psittaci is difficult to detect with standard staining techniques.

Treatment

Psittacosis is treated effectively with antibiotics that inhibit protein synthesis, mainly tetracyclines and macrolides. Early treatment is critical to prevent severe respiratory complications.