Haemolymph parasite of the shore crab Carcinus maenas: pathology, ultrastructure and observations on crustacean haplosporidians

Abstract

A protozoan parasite with some features of haplosporidians is described from the European shore crab Carcinus maenas. The parasite establishes a systemic infection through the haemal sinuses and connective tissues. Intracellular stages of the parasite were found within reserve inclusion, connective tissue, and muscle cells, while free forms were present in all haemal spaces. A uninucleate stage appeared to develop to a multinucleate plasmodial stage following multiple mitotic divisions of the nucleus. Histopathology also indicated that nuclear division may occur to form multinucleate plasmodia, in connective tissue, reserve inclusion and muscle cells, the multinucleate plasmodium being enclosed in the host-cell plasma membrane. It appears that the multinucleate plasmodium may then undergo internal cleavages which result in plasmodial fragmentation to form many uninucleate stages. Both stages, but particularly the uninucleate stage, contained cytoplasmic, large, ovoid, dense vesicles (DVs), some of which contained an internal membrane separating the medulla from the cortex, as in haplosporosomes. Golgi-like cisternae, closely associated with the nuclear membrane, formed DVs and haplosporosome-like bodies (HLBs), superficially resembling viruses. Infrequently, HLBs may condense to form haplosporosomes. The DVs, as in spores of some Haplosporidium spp. and paramyxeans, may give rise to, and are homologous with, haplosporosomes. Other features, such as the presence of an intranuclear mitotic spindle, lipid droplets, and attachment of DVs and haplosporosomes to the nuclear membrane, indicate that the C. maenas parasite is a haplosporidian. A similar organism reported from the haemolymph of spot prawns Pandalus spp., and haplosporidians reported from prawns Penaeus vannamei and crabs Callinectes sapidus may belong to this group. It is concluded that the well-characterised haplosporidians of molluscs and some other invertebrates may not be characteristic of the whole phylum, and that morphologically and developmentally similar organisms may also be haplosporidians, whether they have haplosporosomes or not.

Lineage-specific molecular probing reveals novel diversity and ecological partitioning of haplosporidians

“…Periodic occurrence and dispersal may also pose difficulties in detection. For example, H. littoralis (Figure 1c) is present and monitored in C. maenas in Newton's Cove, yet was not detected in our libraries, possibly due to the fact that transmission stages are not released from infected hosts (Stentiford et al, 2004(Stentiford et al, , 2013 or because two nucleotide mismatches are present between the primers and the H. littoralis sequence. It is a priority for future work to determine to what extent molecular detection of haplosporidian lineages can be associated with actual infections and potential for disease.…”

“…There are currently four recognised haplosporidian genera: (1) Bonamia: four described species, all economically important oyster parasites in temperate waters; (2) Minchinia: a sparsely recorded genus of five species with sequence data from molluscs from the US Atlantic coast, Western Australia and Europe; (3) Urosporidium: one described species with sequence data (U. crescens; (Flores et al, 1996) and another sequenced specimen (Reece et al, 2004), both occurring as hyperparasites of trematode worms; and (4) Haplosporidium: the most intensively studied and diverse genus (approximately 40 species to date) and perhaps paraphyletic (Burreson and Ford, 2004). Most known members of the genus infect molluscs, but some infect crustaceans (Burreson and Ford, 2004;Stentiford et al, 2004) and annelids (Siddall and Aguado, 2006). A minority of lineages infect freshwater molluscs (Molloy et al, 2012).…”

“…(Pichot et al, 1980;Carnegie et al, 2006)) and agents of several decapod crustacean diseases (Stentiford et al, 2004;Utari et al, 2012). The reticulate amoebae, Filoreta and Gromia, are the closest known free-living relatives; phytomyxids, vampyrellids and other Cercozoa are more distantly related (Cavalier-Smith and Chao, 2003;Bass et al, 2009).…”

Paramarteilia canceri sp. n. (Cercozoa) in the European edible crab (Cancer pagurus) with a proposal for the revision of the order Paramyxida Chatton, 1911

“…Larsson and Køie (2005) suggested that the inclusion bodies in cell 5 of Paramyxoides spores were haplosporosomes, despite lacking a medul-la, typical of haplosporosomes. They may be haplosporosome-like bodies similar to those in a haplosporidian parasite of Carcinus maenas (see Stentiford et al 2004). Similar structures to those in cell 5 of Paramyxoides nephtys reported by Larsson and Køie (2005) are referred to as "rod-like structures" in cell 4 of Marteilia spp.…”

Inter-relationships of haplosporidians deduced from ultrastructural studies

“…Studies indicate that a spot prawn parasite (SPP) in Pandalus spp. (Reece et al 2000, Bower & Meyer 2002, and another protistan from crabs (Carcinus maenas) (Stentiford et al 2004), are also haplosporidians. A molecular study (Reece & Stokes 2003) places the multi-nucleate stage of a haplosporidian of New Zealand abalone (Haliotis iris) parasite (NZAP) , as phylogenetically basal to Urosporidium spp., Haplosporidium spp., Bonamia spp., and Minchinia spp.…”