Comparison of in vitro growth characteristics of ten isolates of infectious haematopoietic necrosis virus.

Ten isolates of infectious haematopoietic necrosis from salmonid fishes of different locations on the West Coast of North America from California to Alaska were compared by plaque size, single-step growth curves at 15 and 18 degrees C, rate of appearance of cytopathic effects in cell cultures, and growth over a range of temperatures. All isolates were distinguishable on the basis of each growth characteristic examined. The CO isolate from the Sacramento River drainage of California was the most singular of the 10 because of its diminutive plaque size and sensitivity to slightly elevated temperatures. The mean plaque diameter of the 10 isolates increased as the latitude of the geographic source of the isolate increased. Although the maximum titre obtained by all isolates was depressed at temperatures above approximately 18 degrees C, half of the isolates were not inhibited by temperatures as low as 0.5 degree C.