Chlamydia immunoreactivity in birds with psittacosis: localization of chlamydiae by the peroxidase-antiperoxidase method.

Diagnosis of psittacosis (infection with Chlamydia psittaci) has traditionally been dependent upon culture or demonstration of chlamydiae in tissues by cytochemical stains such as the Gimenez or Macchiavello's stain. In this study, a peroxidase-antiperoxidase (PAP) technique that employs a commercially available monoclonal antibody directed against Chlamydia is used to demonstrate chlamydiae in the necropsy tissues of nine birds. Chlamydiae were identified in air sacs (83%), liver (78%), spleen (78%), small intestines (67%), large intestines (44%), and kidneys (33%). Usually chlamydiae were associated with microscopic lesions, but in 75% of large intestines examined, organisms were identified within the lumen of histologically normal intestine. PAP studies revealed numerous chlamydiae that were inapparent in hematoxylin-and-eosin-stained sections. These results demonstrate the utility and sensitivity of the PAP method in the identification of chlamydiae in microscopic sections.