A Minchinia mercenariae‐like parasite infects cockles Cerastoderma edule in Galicia (NW Spain)

Abstract

The cockle Cerastoderma edule fishery has traditionally been the most important shellfish species in terms of biomass in Galicia (NW Spain). In the course of a survey of the histopathological conditions affecting this species in the Ria of Arousa, a haplosporidan parasite that had not been observed in Galicia was detected in one of the most productive cockle beds of Galicia. Uni- and binucleate cells and multinucleate plasmodia were observed in the connective tissue mainly in the digestive area, gills and gonad. The parasite showed low prevalence, and it was not associated with abnormal cockle mortality. Molecular identification showed that this parasite was closely related to the haplosporidan Minchinia mercenariae that had been reported infecting hard clams Mercenaria mercenaria from the Atlantic coast of the United States. The molecular characterization of its SSU rDNA region allowed obtaining a fragment of 1,796 bp showing 98% homology with M. mercenariae parasite. Phylogenetic analysis supported this identification as this parasite was clustered in the same clade as M. mercenariae from the United States and other M. mercenariae-like sequences from the UK, with bootstrap value of 99%. The occurrence of M. mercenariae-like parasites infecting molluscs outside the United States is confirmed.

Detection of haplosporidian protistan parasites supports an increase to their known diversity, geographic range and bivalve host specificity

“…Haplosporidia-like single cell and plasmodia-like life stages identical to those described in Ramilo et al . (2017) and a spore-like stage (Fig. 2A–F) were observed in the connective tissues of Irish C. edule in a single individual at Flaxfort the nonculture site in June 2010 [0.11% (1/900)].…”

“…A single haplosporidian spp. M. mercenariae-like parasite in C. edule at Flaxfort Strand (2010) and at the C. gigas culture sites Dungarvan and Carlingford Lough (2015) was identified in the PCR products amplified in cockles from the three sites [Accession # KY522823.1 (Ramilo et al ., 2017)] with 97% query coverage and 100% maximum identity and are referred to as ‘Isolates 221, 226 and 228’ in this study.…”

“…Besides their low detection prevalence, a major reason for the lack of detection of novel haplosporidian taxa is thought to be the use of (and increasing reliance on) broadly targeted molecular probes that are unsuitable for the highly divergent genes that characterize parasite groups (Hartikainen et al ., 2014). Despite these obstacles, novel haplosporidians continue to be discovered in host/carrier species and habitats including the recently detected Haplosporidium pinnae in the fan mussel Pinna nobilis in the western Mediterranean Sea, thus highlighting the possibility that a significant diversity of haplosporidians have yet to be discovered (Lynch et al ., 2013, 2014; Arzul and Carnegie, 2015; Pagenkopp Lohan et al ., 2016; Ramilo et al ., 2017; Catanese et al ., 2018).…”

“…Haplosporidium nelsoni , the causative agent of MSX disease in the eastern oyster Crassostrea virginica in North America, was detected for the first time in Irish and Spanish Pacific oysters Crassostrea gigas and in O. edulis in Ireland (Lynch et al ., 2013). In addition, Minchinia mercenariae , reported to cause infections in the hard clam Mercenaria mercenaria from the Atlantic coast of the United States (Ford et al ., 2009), was detected in the common cockle Cerastoderma edule in the Netherlands (Engelsma et al ., 2014) and the UK (Longshaw and Malham, 2013) where it was implicated in host population crashes, and an M. mercenariae -like parasite was recently confirmed in C. edule in Galicia, Spain (Ramilo et al ., 2017).…”

“…Parasites in the phyla Haplosporidia have been reported infecting a number of bivalve hosts from across Europe. Species known to infect C. edule are Haplosporidium edule, Minchinia tapetis and M. mercenariae (Longshaw and Malham, 2013; Ramilo et al ., 2017) and in mussels Minchinia sp. in Mytilus galloprovincialis along the Mediterranean coast of France (Comps and Tige, 1997), Haplosporidium sp.…”