Pseudodiplorchis americanus

Life Cycle

Direct, single host: the American spadefoot toad (Scaphiopus couchii)

Brief periods of rainfall once a year in July/August in S.E. Arizona trigger spadefoot toads to emerge from hibernation to feed and breed in the pools of water that form. When these circumstances arise, encapsulated P. americanus oncomiracidia hatch and emerge from frog urinary bladders and into the water, where the free-swimming infective stage can invade frogs via the nostrils before migrating to the lungs, which, among monogeneans, is a unique pathway. Juveniles travel upwards from the lungs to the oral cavity, then through the digestive tract to finish development, reside, and reproduce in the urinary bladder.

Tinsley, R., & Jackson, H. (1986). Intestinal migration in the life-cycle of Pseudodiplorchis americanus (Monogenea). Parasitology, 93(3), 451-469. doi:10.1017/S0031182000081178

Host Information

This parasite is very specific and only infects the American Spadefoot toad, so its life cycle must be aligned well to the frogs' in order for successful transmission to take place during yearly rainfalls, specifically during the same time of day that the frogs are most active for breeding in pools of water. This creates a delicate balance that could be upset, especially in changing climatic conditions.

Distribution

This parasite is found in deserts in the US, Canadian prairies and northern parts of Mexico.