Assessment of infectious salmon anaemia virus prevalence for different groups of farmed Atlantic salmon, Salmo salar L., in New Brunswick

Infectious salmon anaemia (ISA) virus (ISAV) has been causing disease in New Brunswick since 1996. As a control measure, all fish in an outbreak cage are killed. The objective of this study was to compare ISAV prevalence in cages experiencing an outbreak with healthy cages from the same farm, neighbouring farms and distant farms. Atlantic salmon from five different groups were tested using an RT‐PCR test. Groups included moribund fish from a cage experiencing an outbreak (A), healthy fish from an outbreak cage (B), healthy fish from a negative cage from a farm experiencing an outbreak in a different cage (C), healthy fish from a negative farm near an outbreak farm (D), and healthy fish sampled at a negative farm located in an area with only negative farms (E). Apparent prevalences (standard error) for the different groups (A–E) were 0.94 (±0.026), 0.41 (±0.062), 0.29 (±0.040), 0.08 (±0.037) and 0.08 (±0.037), respectively. All groups were significantly different (P