PNEUMOCYSTIS-CARINII IS NOT UNIVERSALLY TRANSMISSIBLE BETWEEN MAMMALIAN-SPECIES

In a series of five experiments, we attempted to transmit Pneumocystis carinii from ferrets to SCID mice by intratracheal inoculation. Using highly specific and sensitive assay techniques, we could not document infection of SCID mice by P. carinii isolated from ferrets. In contra st, under identical inoculation conditions, P. carinii was easily tran smissible from one SCID mouse to another. These results indicate that P. carinii organisms, at least those isolated from ferrets, have a res tricted host range. The finding of restricted transmission of P. carin ii is consistent with the increasing evidence for host species-specifi c antigenic variation among isolates of P. carinii. If restricted host range is a consistent biological feature of animal-derived P. carinii , it would suggest that P. carinii pneumonitis in humans may not be a zoonosis as previously speculated.