Treatment or Protection Strategies

Chemotherapy
In vitro, P. salmonis is sensitive to a variety of antibiotics including streptomycin, gentamicin, erythromycin, chloramphenicol and oxytetracycline, but shows resistance to penicillin, penicillin G and spectinomycin. However, the use of medicated feed to control intracellular pathogens, including P. salmonis, has been largely unsuccessful, possibly because antibiotic levels may not reach sufficient concentrations within the host cells in vivo. However, injection of broodstock with antibiotics before leaving seawater in order to control the typical "summer SRS outbreak" is common. 

Vaccine development
Although commercial vaccines against P. salmonis are very recently available, there is little published information or field experience on their efficacy or economic value. However, several institutes and pharmaceutical companies, including Intervet, have active research programmes directed towards developing efficacious vaccines.

Management
Outbreaks frequently occur after smolt transfer to seawater, but good management practices do help. Such approaches include the early removal of mortalities and clinically diseased fish, with appropriate sanitary disposal of blood from harvested fish, reducing fish stocking density and providing periods of site fallowing. Other strategic measures include routine screening of broodstock, rejection of eggs from positive fish and individual incubation of egg batches. Further information regarding horizontal and vertical transmission, pathogenesis, intracellular survival and immunogenicity is needed to support future control strategies. In addition, information on the geographic location and species distribution of P. salmonis among isolates and stocks of fish will be helpful in developing management and control strategies in the future.