Avian cholera on north coast California - Distinctive epizootiological features

Between 1945 and 2001, avian cholera (Pasteurella multocida infection) was confirmed at 27 epizootics in 18 different years on northcoastal California. Estimated mortality ranged from I to 6750 birds per site, with a median total mortality of about 1000 birds per year. Eight epizootics involved <150 birds; thus, minor epizootics were common. Annual total wildfowl mortality ranged from 0.4% to 7.0% of estimated live populations; median annual mortality for American coots (Fulica americana) (11.5%) surpassed that of tundra swans (Cygnus columbianus) (0.2%) and ducks (0.2%). Coots comprised >50% of total wildfowl mortality in 16 of 17 epizootics. Overall, coots comprised 82% of known avian cholera mortality, but only 34% of the live wildfowl present; ducks and swans died much less frequently. Wildfowl at one site consistently died in a sequential pattern; there was no sequential mortality at other sites.