PLISTOPHORA MYOTROPHICA SPEC. NOV., CAUSING HIGH MORTALITY IN THE COMMON TOAD BUFO BUFO L., WITH NOTES ON THE MAINTENANCE OF BUFO AND XENOPUS IN THE LABORATORY.

Abstract

SYNOPSIS. Colonies of Bufo bufo kept for pregnancy diagnostic purposes were found infected with a new species of microsporidian, Plistophora myotrophica, causing atrophy of the striated muscles. Lysis of myofibrils by the parasite leads to the formation of fusiform spaces in the fibers packed with microsporidian spores. A cyst wall is not formed. Toads become emaciated and suffer heavy mortality.In experimental infections the sporoplasm hatches in the gut. Fusiform granular bodies, not identifiable as blood cells, are found in the muscle capillaries at 18 days and possibly represent early stages of the parasite. Between 18 and 23 days division of the parasite occurs in the muscle fibers, first by binary fission, then multiple fission and finally by plasmotomy culminating in the formation of sporonts with 16 to 100 nuclei. Separation into sporoblasts precedes spore formation.In old infections phagocytes, which are probably monocytes, infiltrate between the groups of spores and ingest them. Ingested spores which stain differently from their free counterparts, are dead. Muscle regeneration is initiated by the toad, with the formation of long chains of sarcoblasts, sometimes 30 or more in a chain, responsible for the regeneration and redifferentiation of myofibrils.Tadpoles are refractory to infection. As toads normally lead a solitary life the high local incidence in the area from which the toads were collected is explained only if the toads acquire the infection from spore‐contaminated ground in the breeding season.