Invasion of vertebrate lungs by the polystomatid monogeneans Pseudodiplorchis americanus and Neodiplorchis scaphiopodis

Abstract

SUMMARYSome unique features of monogenean biology have emerged from studies on 2 polystomatids which infect spadefoot toads in Arizona, USA: Pseudodiplorchis americanus in Scaphiopus couchii and Neodiplorchis scaphiopodis in S. multiplicatus and S. bombifrons. Transmission is confined to 1–3 nights each summer when the desert-adapted toads enter water to spawn. Encapsulated larvae complete development in utero and hatch within seconds of deposition; their body length (up to 600 μm) is 2–4 times greater than that of most other oncomiracidia, and their swimming life (over 48 h at 25–27 °C) is twice that usual amongst monogeneans. The ciliated oncomiracidia invade the nostrils, a target usually above the water surface and requiring migration over the exposed skin; remarkably they tolerate drying for up to 1 h (at 32 °C, 45% rel. hum.). The larvae migrate via the buccal cavity and glottis to the lungs where juvenile development occurs until early autumn. Migration from the lungs to the urinary bladder (by an as yet undetermined route) is followed by maturation and reproduction during host hibernation, and developing embryos accumulate in preparation for a period of transmission more restricted than that of any other monogenean. No other monogenean is known to exploit the lungs nor to inhabit, successively, anterior and posterior sites of the same adult host individual.