Parasitic dinoflagellate Hematodinium perezi prevalence in larval and juvenile blue crabs Callinectes sapidus from coastal bays of Virginia

Parasitic dinoflagellate Hematodinium in marine decapod crustaceans: a review on current knowledge and future perspectives

Parasitic dinoflagellates of the genus Hematodinium are known to infect various marine crustaceans worldwide, especially crabs and several species of shrimp and lobster. Some of these species are new host species and components of commercial fishery products. These parasitic species are predominantly found in the hemolymph of the host and cause pathological changes and functional damage to organs and tissues, leading to death. In recent years, these parasites have infected important commercially valuable species, particularly in European waters, US waters, Australian waters, and recently in Shandong Peninsula in China. These Hematodinium pathogens were also reported to affect wild shrimp in Chinese waters and in the English North Sea. These rapid spreads affect crustacean aquaculture industries, where they are indeed a significant threat to the sustainability of the aquaculture of important crustaceans. The fishery products industries are also under pressure from the invasion of this pathogen, as the crab meat produced has a bitter taste, which may reduce its marketability. In response to these threats, this review was aimed at providing a broader understanding of the development of parasite distribution and ecological aspects of Hematodinium. In addition, the interaction of these pathogens with their hosts, the environmental drivers of Hematodinium disease, and future research perspectives were discussed.

Extracellular vesicle signatures and protein citrullination are modified in shore crabs (Carcinus maenas) infected with Hematodinium sp

Epizootiologists recurrently encounter symbionts and pathobionts in the haemolymph (blood equivalent) of shellfish. One such group is the dinoflagellate genus Hematodinium, which contains several species that cause debilitating disease in decapod crustaceans. The shore crab Carcinus maenas acts as a mobile reservoir of microparasites, including Hematodinium sp., thereby posing a risk to other co-located commercially important species, e.g. velvet crabs (Necora puber). Despite the widespread prevalence and documented seasonality of Hematodinium infection dynamics, there is a knowledge gap regarding host-pathogen antibiosis, namely, how Hematodinium avoids the host's immune defences. Herein, we interrogated the haemolymph of Hematodinium-positive and Hematodinium-negative crabs for extracellular vesicle (EV) profiles (a proxy for cellular communication), alongside proteomic signatures for post-translational citrullination/deimination performed by arginine deiminases, which can infer a pathologic state. Circulating EV numbers in parasitized crab haemolymph were reduced significantly, accompanied by smaller EV modal size profiles (albeit non-significantly) when compared to Hematodinium-negative controls. Differences were observed for citrullinated/deiminated target proteins in the haemolymph between the parasitized and control crabs, with fewer hits identified overall in the former. Three deiminated proteins specific to parasitized crab haemolymph were actin, Down syndrome cell adhesion molecule (DSCAM), and nitric oxide synthase - factors that contribute to innate immunity. We report, for the first time, Hematodinium sp. could interfere with EV biogenesis, and that protein deimination is a putative mechanism of immune-modulation in crustacean-Hematodinium interactions.

Salinity and temperature affect the symbiont profile and host condition of Florida USA blue crabs Callinectes sapidus

Subtropical Florida blue crabs, Callinectes sapidus, exhibit differing life history traits compared to their temperate counterparts, likely influencing symbiont infection dynamics. Little information exists for Florida C. sapidus symbiont profiles, their distribution among various habitats, and influence on crab condition. Using histopathology, genomics, and transmission electron microscopy, we describe the first symbiont profiles for Florida C. sapidus occupying freshwater to marine habitats. Twelve symbiont groups were identified from 409 crabs including ciliophorans, digenean, microsporidian, Haplosporidia, Hematodinium sp., Nematoda, filamentous bacteria, gregarine, Callinectes sapidus nudivirus, Octolasmis sp., Cambarincola sp., and putative microcell. Overall, 78% of C. sapidus were documented with one or more symbiont groups demonstrating high infection rates in wild populations. Environmental variables water temperature and salinity explained 48% of the variation in symbiont groups among Florida habitats, and salinity was positively correlated with C. sapidus symbiont diversity. This suggests freshwater C. sapidus possess fewer symbionts and represent healthier individuals compared to saltwater populations. Crab condition was examined using the reflex action mortality predictor (RAMP) to determine if reflex impairment could be linked to symbiont prevalence. Symbionts were found positively correlated with crab condition, and impaired crabs were more likely to host symbionts, demonstrating symbiont inclusion may boost predictive ability of the RAMP application. The microsporidian symbiont group had a particularly strong effect on C. sapidus reflex response, and impairment was on average 1.57 times higher compared to all other symbiont groups. Our findings demonstrate the importance of considering full symbiont profiles and their associations with a spatially and temporally variable environment to fully assess C. sapidus population health.

Natural Transmission of Hematodinium perezi in Juvenile Blue Crabs (Callinectes sapidus) in the Laboratory

Hematodinium perezi is a dinoflagellate endoparasitic in marine crustaceans, primarily decapods. It occurs in juvenile blue crabs, Callinectes sapidus, at high prevalence levels and has severe pathogenic effects in this host. The life history outside the host has not been experimentally investigated and, until now, transmission using dinospores has not been successful. We investigated the natural transmission dynamics of H. perezi in the laboratory using small juvenile crabs, which are highly susceptible to infection in the field, and elevated temperatures, which are known to stimulate dinospore production. Natural water-borne transmission to naïve crabs varied between 7-100% and was not correlated with dinospore densities measured from their aquaria water. Infections appeared to develop quickly in naïve hosts at 25 °C, suggesting that elevated temperatures as seen in the late summer and early autumn have a strong influence on the transmission of H. perezi in natural systems.