Ultrastructural and molecular characterization of Pneumocystis carinii isolated from a rhesus monkey (Macaca mulatta)

High levels of heterogeneity have been observed among isolates of Pneumocys tis carinii derived from different mammalian host species. We report the ch aracterization of P. carinii isolated from a rhesus monkey (Macaca mulatta) , which was immunosuppressed as a result of infection with a chimeric simia n-human immunodeficiency virus (SHIVsbg). Histopathological examination sho wed evidence of severe P. carinii pneumonia with a large predominance of tr ophozoite forms. Alveolitis consisted of typical foamy, honeycomb exudate, with only a few alveolar macrophages. The lung inflammatory response was ra ther moderate without type-2 pneumocyte hyperplasia or collagenosis. P, car inii organisms were sometimes observed in the bronchiolar lumen. Ultrastruc turally, macaque-derived P; carinii was more similar to human- or rabbit-de rived parasites than to mouse-derived P, carinii. Molecular studies were ca rried out on the macaque-derived P, carinii DNA at two genetic loci: the ge nes encoding the mitochondrial large subunit ribosomal RNA (mt LSU rRNA) an d the mitochondrial small subunit ribosomal RNA (mt SSU rRNA), Comparison o f the DNA sequences with those from P. carinii isolated from eight other ho st species demonstrated that the macaque-derived P, carinii was genetically distinct at both loci, and was more closely related to human-derived P, ca rinii than to P, carinii derived from non-primate sources. We propose that macaque-derived P, carinii be named Pneumocystis carinii f.sp. macacae.