Microsporidian hyperparasites and bacteria associated with Pseudodiplorchis americanus (Monogenea: Polystomatidae)

Abstract

This is the first report of a microsporidian hyperparasite in a monogenean. Every stage in the life cycle of the polystomatid Pseudodiplorchis americanus was infected (prevalence 11%). Ultrastructural examination revealed microsporidians within most tissues, but the heaviest aggregations occurred in the external surface layer of the larvae, especially the tegumental ciliated cells where they may interfere with exciliation. Adult worms also harboured a bacterium (prevalence 55%) that was largely restricted to the gut lumen and therefore probably ingested. Transmission of the microsporidian may occur via ingestion of host tissue, but infection within the germ cells and encapsulated embryos in utero demonstrates transovarian and trans-uterine transfer. The oncomiracidia can be already infected at the time of transmission, carrying the microsporidians to newly invaded vertebrate hosts. Heavy microsporidian infections are associated with cellular damage in developing and adult monogeneans and may have a direct effect on the population biology of P. americanus.