First report of a trematode infection in an invasive population of Pomacea maculata: Evidence of a phaneropsolid (Trematoda: Microphalloidea) and recommended methods for surveillance

Giant apple snails, Pomacea maculata (Caenogastropoda: Ampullariidae), are native to South America but are now invasively established in subtropical freshwater habitats worldwide. In May 2017, P. maculata from an urban pond in Mobile, Alabama, USA were found infected with a larval trematode, prompting further collections to determine prevalence and investigate effects of infection by snail sex and size. In total, 284 snails (n = 184 female, n = 100 male) were collected in May, August, and October of 2017 and 2018. Of these, 60 females and 23 males were infected with prevalence per sampling event ranging from 4 to 67 % in females and 0 to 47 % in males. Across all collections, average prevalence was 29.1 %, exceeding values previously reported for Pomacea spp. in their native or invasive ranges. Infection prevalence was positively associated with snail mass, especially in males, suggesting larger individuals are more likely to serve as hosts. Phylogenetic analyses of partial 28S ribosomal DNA sequences identified the trematode as a member of Phaneropsolidae (Microphalloidea), a family that infects ampullariid snails in their native range and includes Phaneropsolus spp., some of which are zoonotic. Comparisons of cercarial morphology against published descriptions complement the molecular results. This is the first report of a trematode infecting an invasive population of P. maculata. These methods and findings demonstrate the utility of simple tissue screening and 28S rDNA sequence data in the rapid detection and molecular identification of larval trematodes collected from invasive populations of snails, facilitated by a newly designed broad-range digenean primer.