Resistance of the Manila clam ( Venerupis philippinarum) to infection with Mikrocytos mackini

Manila clams ( Venerupis philippinarum) challenged in laboratory trials via bath exposure proved to be resistant to infections with Mikrocytos mackini (protistan parasite of unknown taxonomic affiliation), while Pacific oysters ( Crassostrea gigas) challenged simultaneously using identical conditions developed infections. Although M. mackini was detected by a nucleic acid pathogen specific (PCR) assay in 10–30% of the challenged V. philippinarum that were sampled soon after exposure (0–48 h, n = 40), all of the subsequent V. philippinarum ( n = 62) sampled 9–17 weeks post-exposure tested negative for M. mackini by PCR assay. Prevalence of infection for the exposed C. gigas ( n = 100) during this same period ranged from 50% to 100% by PCR assay. Infection was confirmed in the oysters (58%, n = 60) by a digoxigenin-labelled DNA probe designed to detect M. mackini by in situ hybridization, but M. mackini was not found in any of the exposed Manila clams ( n = 63) using this technique.