Larval Digenean Parasitizing Amphibian Hosts from the Argentinian Chaco Region

The diversity of larval digenetic trematodes can provide information on one or more intermediate hosts prior to maturation into the definitive host; on host activity and distribution; and in some cases, on environmental perturbations. In this context, the goal of the present study was to analyse the trematode larvae found in adult amphibians collected from the Argentinian Chaco Region. Few studies have been reported on the systematics of larval digeneans in amphibians.

A total of 167 specimens of frogs (Leptodactylus macrosternum, Leptodactylus latinasus, Lepidobatrachus laevis, Lepidobatrachus llanensis and Lysapsus limellum) and toads (Rhinella bergi) were examined for larval digeneans. Frogs and toads were collected in two Argentinian ecoregions (Dry Chaco and Humid Chaco); between June 2002 and December 2019. Morphology of each taxon was studied in detail using light microscopy and scanning electron microscopy (SEM).

Fourteen different taxa of the families Diplostomidae (Alariinae gen sp., Didelphodiplostomum sp., Pharingostomoides sp. and Tylodelphys sp.), Proterodiplostomidae (Heterodiplostomum lanceolatum), and Strigeidae (Strigea spp.) were found infecting the body cavity, mesentery, muscle, fluid in the spinal cord canal, and cranial cavity of amphibians. All species are described and illustrated, and their life cycles are briefly discussed.

These infections provide new information on the morphology, morphometry, and composition of the diversity of mesocercariae and metacercariae in amphibians, thus contributing to the knowledge of potential intermediate hosts. In addition, our results serve as an indicator of parasite and host biodiversity in different ecoregions of the Gran Chaco.