Transmission

Shedding of the infectious agent among birds with latent chlamydiosis may be activated by several stress factors, including shipping, crowding, chilling, and breeding. Birds can appear healthy but be carriers of C. psittaci and can shed the organism intermittently. When shedding occurs, the organism is excreted in the feces and nasal discharges of infected birds. The organism is resistant to drying and can remain infectious for several months.

Clinical Signs

For caged birds, the time between exposure to C. psittaci and the onset of illness ranges from 3 days to several weeks. However, latent infections are common among birds, and active disease may appear years after exposure. C. psittaci infection in birds can be asymptomatic or can result in an acute, subacute, or chronic clinical disease. Whether the bird exhibits clinical signs of illness or dies depends on the species of bird, virulence of the strain, infectious dose, stress factors, age, and extent of treatment or prophylaxis.

Birds with clinical signs of AC typically have manifestations (e.g., lethargy, anorexia, and ruffled feathers) consistent with those of other systemic illnesses. Other signs associated with AC include serous or mucopurulent ocular or nasal discharge, diarrhea, and excretion of green to yellow-green urates. Anorectic birds may produce sparse, dark green droppings. Birds can die soon after onset of illness or, as the disease progresses, can become emaciated and dehydrated before death.

Diagnosis

Several diagnostic methods are available for identifying AC in birds (Appendix A). A confirmed case of AC is defined as infection with C. psittaci on the basis of at least one of the following laboratory results: a) isolation of C. psittaci from a clinical specimen, b) identification of chlamydial antigen by immunofluorescence (fluorescent antibody [FA]) of the bird’s tissues, c) a greater than fourfold change in serologic titer in two specimens from the bird obtained at least 2 weeks apart and assayed simultaneously at the same laboratory, or d) identification of C. psittaci within macrophages in smears stained with Gimenez or Macchiavellos stain or sections of the bird’s tissues.

A probable case of AC is defined as C. psittaci infection in a bird that has clinical illness compatible with AC and at least one of the following laboratory results: a) a single high serologic titer in one or more specimens obtained after the onset of signs or b) the presence of C. psittaci antigen (identified by enzyme-linked immunosorbent assay [ELISA] or FA) in feces, a cloacal swab, or respiratory or ocular exudates.

A suspected case of AC is defined as a) clinical illness compatible with AC that is epidemiologically linked to another case in a human or bird but that is not laboratory confirmed, b) an asymptomatic infection in a bird with a single high serologic titer or detection of chlamydial antigen, c) illness in a bird that has positive results for infection on the basis of a nonstandardized test or a new investigational test, or d) a clinical illness compatible with chlamydiosis that is responsive to appropriate therapy.

Treatment

Veterinarians can choose from three types of methods for treating birds with AC — medicated feed (chlortetracycline), oral or parenteral treatment (doxycycline or oxytetracycline), and experimental treatment (fluoroquinolones, late-generation macrolides, pharmacist-compounded injectable doxycycline, and doxycycline-medicated feed) (Appendix B). Although these protocols are usually successful, knowledge about AC treatment is evolving, and no treatment protocol guarantees safe treatment or complete elimination of infection by the etiologic agent C. psittaci in all bird species. Therefore, treatment should be supervised by a licensed veterinarian.