Denman Island disease (causative agent Mikrocytos mackini) in a new host, Kumamoto oysters Crassostrea sikamea.

Mikrocytos mackini, causative agent of Denman Island disease in Pacific oysters Crassostrea gigas and other oyster species, was found in 2011 in a previously unreported host, the Kumamoto oyster C. sikamea, in Humboldt Bay, California, USA. The detection was also the first reported finding of M. mackini in California. Prevalence was estimated as high as approximately 27% from pooled samples analyzed by PCR. Higher prevalence appeared related to longer residence time in the bay and somewhat colder than typical winter seawater temperatures. No M. mackini was detected in Humboldt Bay juvenile Kumamoto oysters or Pacific oyster brood or seed stock in 2011 or 2012.