A Hematodinium-like dinoflagellate infection of the Norway lobster Nephrops norvegicus: observations on pathology and progression of infection

The discovery of a Hematodinium-like dinoflagellate infecting Nephrops norvegicus has led to a pathological investigation into the effects on the host and the apparent progression of the disease syndrome. The parasite is systemic, invading the haemocoel and the connective tissues of most organs via the haemal spaces. An increase in the combined number of parasites and haemocytes in the haemolymph was due to an increase in the relative proportion of dinoflagellates and suggested a reduction in numbers of haemocytes. These parameters did not correlate directly with severity. Comparison of the level to which tissues were invaded and the relationship between haemocyte and parasite numbers in the haemolymph suggests that at least some organs may be invaded very early in infection, if not before parasites enter the Ohaemolymph. There was evidence of host cellular defence reactions, in the form of haemocyte encapsulations in the gills and heart, and phagocytosis of dinoflagellates by the fixed phagocytes of the hepatopancreas.