Visceral lesions caused by Yersinia pseudotuberculosis, serotype II, in different species of bird.

The size and distribution of histological lesions was studied in 14 cases of avian pseudotuberculosis using a combination of serotype-specific immunohistochemistry and image analysis. The material was derived from recent and archival cases in six canaries (Serinus canaria), two zebra finches (Poephila guttata), three psittaciformes (a kaka, Nestor meriondalis, one rainbow lorikeet, Trichoglossus mollucanus, and one budgerigar, Melopsittacus undulatus), and three New Zealand wood pigeons (Hemiphaga novaeseelandiae). The disease observed in the passerine species appeared to have an acute clinical course and the bacterial lesions were predominately enteric. In the pigeons and the psittaciformes examined, the clinical course of the disease was more chronic in nature and involved the liver and spleen. A correlation was found between the amount of stainable iron in the liver of affected birds and the area of bacterial lesions. All of the 11 strains of Yersinia pseudotuberculosis isolated from fresh necropsy material were serotype II, as determined using a standard serum agglutination test. Immunohistochemistry indicated the presence of antigen(s) common to serotype II in histological material from confirmed cases and in another three cases where the organism had been cultured but the serotype not specified. The in vitro virulence characteristics and plasmid profiles of Y. pseudotuberculosis isolates were also determined.