Rhodococcus equi causes severe pyogranulomatous pneumonia in foals. This facultative intracellular pathogen produces similar lesions in immunocompromised humans, particularly in AIDS patients. Virulent strains of R. equi bear a large plasmid that is required for intracellular survival within macrophages and for virulence in foals and mice. Only two plasmid-encoded proteins have been described previously; a 15-to 17-kDa surface protein designated virulence-associated protein A (VapA) and an antigenically related 20-kDa protein (herein designated VapB). These two proteins are not expressed by the same R. equi isolate. We describe here the substantial similarity between VapA and VapB. Moreover, we identify three additional genes carried on the virulence plasmid, The nocardioform actinomycete, Rhodococcus equi, is an important pulmonary pathogen in foals and in human patients with AIDS. This gram-positive bacterium is a facultative intracellular pathogen that persists and multiplies within macrophages. Intracellular survival is considered to be necessary for the development of disease, which is characterized by severe and sometimes fatal pneumonia in both humans and foals (5,17).Clinical isolates of R. equi contain a large plasmid ranging in size from 80 to 90 kb in equine or 30 to 100 kb in human AIDS isolates (25,30). The large plasmid is essential for virulence in mice and foals and for intracellular survival in murine and equine macrophages (9). Plasmid curing by repeated passage during in vitro culture at 37°C eliminates the virulent phenotype (9, 27). These findings indicate that the plasmid encodes proteins that are necessary for virulence.Only two proteins encoded by R. equi virulence plasmids have been described to date. Equine isolates express a 15-to 17-kDa protein (VapA) that appears as a characteristic broad band in sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) gels (20,26,29). Human R. equi isolates from AIDS patients generally express either VapA or an antigenically related 20-kDa protein (25). The 20-kDa protein is expressed by isolates from pigs as well as humans. No R. equi isolate has been shown to express both VapA and the 20-kDa protein. However, antigenic cross-reactivity between VapA and the 20-kDa protein has been demonstrated using immunoblots and serum from infected foals (25). The similarity of VapA and the 20-kDa plasmid-encoded proteins raises the possibility that the two proteins have analogous functions in different strains of R. equi.VapA and the 20-kDa protein are located on the bacterial surface, and expression is reported to be thermally and pH regulated (22,24). Specifically, VapA and the 20-kDa protein can be detected when R. equi is cultured at 38°C but not when cultured at 30°C, and expression at 38°C is observed only if the pH of the medium is decreased below 8 (22). These characteristics suggest that expression is upregulated in the mammalian host and intracellularly where VapA or the 20-kDa protein would play a role in the pathogenesis of rhodococcal p...

Findings suggest that administration of human albumin solution in healthy dogs with normal serum albumin concentrations may result in signs of a type III hypersensitivity reaction.

No abstract

Results suggested that dogs developed a pronounced IgG response following exposure to HA and that some dogs with no history of HA administration were positive for anti-HA IgG.

No abstract