Immune parameters in carpet shell clams naturally infected with Perkinsus atlanticus.

Defence parameters of non-infected clams (Ruditapes decussatus) and clams heavily infected with Perkinsus atlanticus were assessed. Cellular (haemocyte density and phagocytic activity) and humoral (lysozyme and anti-bacterial activities, protein concentration and agglutination titre) parameters were measured in clams collected in an area enzootic for P. atlanticus. The infection intensity of each clam was assessed, and the immune parameters measured in the most infected clams were compared with those measured in the non-infected ones. Only the serum anti-bacterial activity and the agglutination titre were significantly different between infected and non-infected clams. The phagocytic rate, haemocyte density, lysozyme concentration and protein concentration were not statistically different but they showed the same trend in the two trials performed. Phagocytic rate, haemocyte concentration and anti-bacterial activity were higher in non-infected clams, while they had lower lysozyme concentration, serum protein concentration and agglutination titre than infected clams. Although infected and healthy clams were not different for every parameter measured, probably due to the high variability among individuals, P. atlanticus seems to affect the clam immune system, at least in advanced stages of the infection.