Prevalence of the Aleutian mink disease virus infection in Nova Scotia, Canada

Despite many years of testing mink for serum antibodies against the Aleutian mink disease virus (AMDV) by counterimmunoelectrophoresis (CIEP) and elimination of reactors, this virus has remained the number one disease threat for the mink industry in Nova Scotia (NS). The objective of this study was to analyze CIEP test results to determine the success of the AMDV-control strategy in NS. A total of 2,964,920 CIEP test results from 82 ranches, spanning an eight-year period between 1998 and 2005, were analyzed. This survey included approximately 60% of the active ranchers in the province. The number of ranchers that tested their animals was 42 in 1998, gradually increased to 58 in 2003 and then showed some decline. The overall proportion of CIEP-positive mink was 3.34%, and varied between 5.22% in 1999 and 1.35% in 2005. The proportion of infected ranches ranged between 23.8% in 1998 and 70.7% in 2003. The overall trend was for a smaller proportion of infected animals but a larger proportion of infected ranches during this time period. Of the 82 ranches, 24 (29.3%) had negative CIEP in all tests, 15 (18.3%) had CIEP positive animals in every year tested, and 43 (52.4%) had positive and negative results in different years, indicating that AMDV infection was widespread in NS. There were 23 infected ranches with 8 years of uninterrupted testing. These ranchers performed 75.8% of the total samples tested (2,246,711), implying that they have diligently been trying to eradicate the virus. Infection persisted on three of these ranches for the entire 8 year period, and only two of the ranches remained CIEP negative for longer than four years. The average percentage of CIEP-positive mink on these ranches was 2.2, which was lower than 6.35% for the 33 infected ranches with occasional testing, and 73.6% and 82.4% for two ranches that had never used the CIEP test, showing that persistent test-and-removal strategy has been effective in reducing the prevalence of infected animals but has failed to eradicate the virus from most of the infected ranches.