Whole clam culture as a quantitative diagnostic procedure of Perkinsus atlanticus (Apicomplexa, Perkinsea) in clams Ruditapes decussatus

The protozoan parasite Perkinsus atlanticus (Azevedo, 1989) causes severe losses among cultured clams, Ruditapes decussatus. This parasite is routinely diagnosed by means of histology or incubation of gills in fluid thioglycollate medium. However, in order to develop models of experimental reproduction of the disease, a procedure for infection intensity evaluation was required. Thus, a diagnostic method has been developed, based on the culture of all clam tissues in fluid thioglycollate medium, followed by sodium hydroxide lysis, and iodine staining of the parasites on cellulose filters. This method was compared with histology. Results suggest that histology is not sensitive enough to detect low levels of infection. The whole-clam culture technique allows detection of low levels or early infection of clams by P. atlanticus. Moreover, this method provides a quantification of infection intensity as number of parasites per gramme wet weight tissue.