Gross and microscopic pathology associated with large cavernous lesions in muscle of Chinook salmon from Lake Ontario.

Since 1999, eight adult Chinook salmon (Onchorhynchus tshawytscha) from Lake Ontario with large, focal, cavernous, fluid-filled muscle lesions have been examined in our respective laboratories. Gross and microscopic examination, cytology, and bacteriology were performed. Microscopically the lesions were consistent with chronic abscesses. Cytologic evaluation revealed diplomonad flagellate Spironucleus within these lesions. We provide a description of the gross and microscopic pathology associated with the cavernous lesions.

An unusual koi herpesvirus associated with a mortality event of common carp Cyprinus carpio in New York State, USA.

Koi herpesvirus (KHV), a highly contagious and lethal virus that affects both koi (Cyprinus carpio koi) and common carp (Cyprinus carpio), was isolated in 1998 from two outbreaks of koi suffering mass mortality in New York State, USA, and in Israel. The disease had been described as early as 1996 in Europe. In July 2004, this virus was found associated with a mass mortality event in wild common carp in the Chadakoin River, New York, USA (42 degrees 07' N, 79 degrees W). Affected fish typically showed marked hyperplasia of gill tissues, abdominal adhesions, and severe multifocal to diffuse external hemorrhages. The virus isolated in this outbreak was somewhat unusual in that it initially replicated well in fathead minnow cell cultures, which is typical of spring viremia of carp virus. Testing at the National Veterinary Services Laboratories, Ames, Iowa, USA, confirmed the virus's identity to be KHV. Koi herpesvirus is not currently on the OIE (World Organisation for Animal Health) list of notifiable diseases; however, it is capable of causing mass mortality in susceptible fish at permissive temperatures.