Infection of Hydra by Microsporidia

A microsporidian infection in a laboratory clone of Hydra littoralis has been observed, and the parasite has been tentatively identified as a species of Plistophora. Infected hydra continue to bud and regenerate normally and show no significant physiological or morphological changes. Sexual crossing of infected and non‐infected animals shows that the infection is transmitted by the ovum but not by the sperm. Continuous exposure of infected hydra to Fumidil B in solution resulted in the disappearance of all Plistophora spores after a five week period of treatment, and the clones of the treated animals have remained parasite‐free for more than a year.