Comparison of assessment methods used to diagnose Hematodinium sp. infections in Cancer pagurus

Ní Chualáin, C., and Robinson, M. 2011. Comparison of assessment methods used to diagnose Hematodinium sp. infections in Cancer pagurus. – ICES Journal of Marine Science, 68: . Endoparasitic dinoflagellates of the genus Hematodinium have recently gained attention as significant pathogens of the brown crab Cancer pagurus in Ireland. Patent infections, which are characterized by a hyperpigmented carapace and moribund condition, are limited to the discrete periods when macroscopic identification is possible. Three methods are assessed for diagnosing Hematodinium sp. infections in brown crab at the times when macroscopic identification is not always possible. Haemolymph smears, histological sections of gill, heart, midgut, hepatopancreas, muscle, and gonad, and a polymerase chain reaction (PCR) assay provided virtually equivalent accuracy in gauging infection prevalence, regardless of season. Sequences of PCR amplicons from the 18S ribosomal RNA gene confirmed the identity of the parasite as belonging to the genus Hematodinium. Infection intensity values (<1–87%) obtained from haemolymph smears underscored infection levels within tissues, 90% of which contained advanced levels of infection. Alterations to tissues of infected crabs included haemocytopoenia, oedema, which caused dilation of the haemal sinuses resulting in pressure necrosis to the connective tissues around the oocytes, myocardial bundles, and hepatopancreatic tubules. The claw muscle of infected animals contained the fewest parasites.

Characterization of red sternum syndrome in mud crab farms from Thailand

Samples of abnormal mud crabs, Scylla serrata (Forskål, 1755) (Decapoda: Portunidae), were collected from crab farms in Samutsongkhram Province, Thailand. These crabs had hard carapaces, red chelipeds and joints, pale hepatopancreas, gills, and soft muscles. They were almost immobile and finally died. The haemolymph revealed three stages of the syndrome, namely orange, orange-white, and milky-white in colors. The haemolymph, integument, hepatopancreas, gills, abdominal and claw muscle, stomach, and heart were dissected and histologically examined using transmission and scanning electron microscopy. Closer examinations found infection with rod-, curve rod-, or coccus-shape bacteria with thin and thick cell walls in all investigated organs and haemolymph. Isolation of the microorganisms from the infected tissues of red sternum syndrome crabs resulted in five types of bacteria. No microorganism growth was observed in normal crabs. Interestingly, the types of isolated bacteria can be classified according to the severity of the disease. Additionally, the degree of bacterial infection found was consistent with the stages of the disease. It was postulated that the bacteria entered the crabs via the gills, and then migrated through circulating haemocytes, before reaching the internal organs.