Transmission Dynamics of Aleutian Mink Disease Virus on a Farm Under Test and Removal Scheme
One-hundred black female mink naturally infected with the Aleutian mink disease virus (AMDV) were monitored between Nov. 2005 and Feb. 2008. Animals were tested for antibodies against the virus by counter-immunoelectrophoresis (CIEP) and for serum globulin level by the iodine agglutination test (IAT) on nine occasions. CIEP and IAT tests were conducted twice each year on kits at 4 and 7 months of age. The prevalence of CIEP positive adult females and kits was 12% and 20.9% (n=411) in 2006, respectively, but one female and none of the kits (n=491) were seropositive in 2007. IAT positive cases ranged between 14.1% and 80.7% in adults and between 17.0% and 57.6% in kids, suggesting infection by pathogens other than AMDV. Three of the seropositive females cleared the virus and were considered to be resistant, although they continued producing antibodies until pelted at 34 months of age. The pattern of viral transmission among individuals which were in contact with one another was complex. The virus was not transmitted from two infected males to five seronegative females to which they were mated. There was a significantly higher incidence of CIEP positive kits from seropositive dams in 2006 (63.4%) compared with kits from seronegative parents (16.8%), showing transplacental transmission of the virus. All eight progeny of the only infected male in 2006 were CIEP- and PCR-positive, implying that the male possibly transmitted susceptible gene(s) to his progeny. Estimates of heritability for the CIEP-positive kits at 4 and 7 months of age were 0.573 and 0.497, respectively, suggesting the strong contribution of the host genetics to this trait. It was concluded that resistance to infection played a more important role than the survival rate of infected individuals on the herd’s health status. Measures of reproduction were not affected by the IAT scores of the dams.