AN EPIDEMIC OF NEWCASTLE-DISEASE IN DOUBLE-CRESTED CORMORANTS FROM SASKATCHEWAN

A Newcastle disease epidemic in double-crested cormorants (Phalacrocor ax auritus) occurred in July and August 1995, during a 1994-96 study o f a breeding colony of this species on Dore Lake (Saskatchewan, Canada ). Clinical signs and mortality were observed from a tunnel-and-blind system, and moribund and freshly dead birds were examined virologicall y. Yolks from cormorant eggs and sera from cormorants and other birds were tested for hemagglutination inhibiting antibodies to Newcastle di sease virus (NDV). Evidence of Newcastle disease was limited to juveni le double-crested cormorants, despite close contact with other birds, including American white pelicans (Pelecanus erythrorhynchos) and gull s (Larus spp.). Clinical signs included limb, head or neck paralysis, head or body tremors, ataxia, and blindness; pathogenic NDV was isolat ed from affected birds. The mortality rate of juvenile cormorants was 32 to 64%, which was high relative to overall first-year mortality in years without epidemics. Thirty-seven of 63 (59%) cormorant sera colle cted during the epidemic tested positive for antibodies to NDV. Antibo dy status of cormorant egg yolks depended on stage of incubation, like ly due to changes in the amount of water in the yolks. The departure o f juvenile cormorants from their nests at 4 wk of age, resulting in an increased contact rate among individuals, may have been important in triggering the epidemic.