Abstract
BackgroundParasitic dinoflagellates of the genus Hematodinium are significant pathogens affecting the global decapod crustacean fishery. Despite this, considerable knowledge gaps exist regarding the life history of the pathogen in vivo, and the role of free living life stages in transmission to naïve hosts.ResultsIn this study, we describe a novel disease in European brown shrimp (Crangon crangon) caused by infection with a parasitic dinoflagellate of the genus Hematodinium. This is the second example host within the Infraorder Caridea (shrimp) and significantly, the first description within the superfamily Crangonoidea. Based upon analysis of the rRNA gene (SSU) and spacers (ITS1), the parasite in C. crangon is the same as that previously described infecting Nephrops norvegicus and Cancer pagurus from European seas, and to the parasite infecting several other commercially important crab species in the Northern Hemisphere. The parasite is however distinct from the type species, H. perezi, found infecting type hosts (Carcinus maenas and Liocarcinus depurator) from nearby sites within Europe. Despite these similarities, the current study has also described for the first time, a bacteria-like endosymbiont within dinospore stages of the parasite infecting shrimp. The endosymbionts were either contained individually within electron lucent vacuoles within the parasite cell cytoplasm, or remained in direct contact with the parasite cytoplasm or in some cases, the nucleoplasm. In all of these cases, no apparent detrimental effects of colonization were observed within the parasite cell.ConclusionsThe presence of bacteria-like endosymbionts within dinospore life stages presumes that the relationship between the dinoflagellate and the bacteria is extended beyond the period of liberation of spores from the infected host shrimp. In this context, a potential role of endosymbiosis in the survival of free-living stages of the parasite is possible. The finding offers a further intriguing insight into the life history of this enigmatic pathogen of marine crustacean hosts and highlights a potential for mixotrophy in the parasitic dinoflagellates contained within the genus Hematodinium.
Highlights
Parasitic dinoflagellates of the genus Hematodinium are significant pathogens affecting the global decapod crustacean fishery
The pathognomonic signs were typical of previous descriptions of Hematodinium spp. infections in crustacean hosts
The hepatopancreas of shrimp assessed using histopathology were co-infected with Crangon crangon bacilliform virus (CcBV), previously described in European C. crangon populations [18,19]
Summary
Parasitic dinoflagellates of the genus Hematodinium are significant pathogens affecting the global decapod crustacean fishery. The host range has been further extended into the infraorder Caridea (subfamily Palaemonoidea) with the description of Hematodiniumlike infections in farmed populations of the palaemonid ridgetail prawn Exopalaemon carinicauda in China [4]. In this first description of a Hematodinium-like dinoflagellate in prawns, the parasite was demonstrated to be likely the same as that causing similar infections in the Chinese swimming crab (Portunus trituberculatus) and mud crab (Scylla serrata) co-cultured in these farms [5,6], suggesting that the parasite may be a host generalist, a point elaborated in recent studies [7,8]. Likewise Pagenkopp Lohan et al [8] report detecting Hematodinium DNA within Caprellid amphipods from estuaries from the east coast of the United States
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