Since late 1980’s, manila clams (Ruditapes philippinarum) have been affected by the Brown Ring Disease (BRD) caused by Vibrio tapetis. Although several studies have investigated the effects of environmental parameters such as salinity, temperature, and sediment on this host-pathogen relationship, the effect of food quality has never been investigated. However, diet influences the physiological and immune responses to pathogens in several bivalve species. The main objective of this study was to investigate the effects of two diets on physiological and immune responses of clams to BRD. Also, sex and gonad maturation were evaluated by histology to examine their effects. Specimens were acclimated four weeks with either T-iso or Chaetoceros calcitrans, two algal species which exhibit differences in their biochemical compositions. Then, clams were injected with Vibrio tapetis, sterilized seawater or not injected, and further monitored for 30 days. Clam tissues were collected at 0, 2, 7, 14 and 30 days post-treatment to assess immune response by evaluating conchiolin deposit stages and shell repair stages. These two parameters were markedly higher in clams injected with V. tapetis compared to other treatments. Preliminary results suggest that sex and maturity influence BRD dynamics whereas the effect of diet would be of minor significance.