Toxoplasmosis in Cold‐Blooded Hosts *

SYNOPSIS. The existence of naturally acquired toxoplasmosis in cold‐blooded animals, tho sometimes claimed, has always been regarded as extremely doubtful, and tests of susceptibility to experimental infection have usually given negative results. Using a strain of human origin (RH), we attempted infection of 7 species of reptiles (red‐eared turtle Pseudemys scripta elegans , horned toad Phrynosoma cornutum , coal skink Eumeces anthrospinus , blue spiny lizard Sceloporus cyanogenys , chamaeleon Anolis carolinensis carolinensis , spectacled caiman Caiman sclerops , iguana Iguana iguani ), and 3 species of amphibia, (American toad Bufo americanus , leopard frog Rana pipiens pipiens , newt Diemectylus viridescens viridescens ). The horned toads, chamaeleons, and toads were kept both at room temperature and 37 C, and the skinks only at 37 C; other species were kept only at room temperature. Inoculation was by intrapcritoneal injection of parasitecontaining ascitic fluid from infected mice. Results were measured by the finding of parasites microscopically and by infection of mice. In toads, infection persisted 7 days: in red‐eared turtles, chamaeleons and the blue spiny lizard 7‐8 days; skinks had a fulminating infection which was fatal in a week or less. Actual reproduction of parasites occurred in both homed toads and skinks kept at 37 C, showing that there was true infection and not simply survival of organisms. These results suggest that natural infections could occur under suitable environmental conditions in horned toads and some other species of lizards.