Assay to Detect the Actinospore and Myxospore Stages of Proliferative Gill Disease in Oligochaetes and Pond Water

With the use of a polymerase chain reaction assay previously developed for Henneguya ictaluri, the myxozoan parasite associated with proliferative gill disease (PGD), a new technique was developed to detect the actinospore stages in pond water samples and in the aquatic oligochaete host Dero digitata. Samples of water and aquatic oligochaetes were collected from 40 commercial ponds containing channel catfish Ictalurus punctatus. Using a previously reported technique to detect H. ictaluri‐infected gills and this new technique, we found 35 out of the 40 ponds had H. ictaluri‐positive oligochaetes, 32 ponds had H. ictaluri‐positive fish, and 25 ponds had water testing positive for H. ictaluri actinospores. This new technique is not only less time‐consuming and labor‐intensive than current methods, it is also sensitive enough to detect the stages of this parasite in oligochaetes or in the water before channel catfish are infected. A detection method such as this one could be used to determine the time to stock ponds or restock ponds after a PGD outbreak has occurred.