Seroprevalence of Actinobacillus (Haemophilus) pleuropneumoniae serotype-1 infection in swine herds in Quebec.

Seroprevalence of Actinobacillus (Haemophilus) pleuropneumoniae serotype-1 infection was evaluated in pigs on 7 farms in Quebec. Commercial cross-bred herds A to G, ranging from 110 to 235 sows and infected with A pleuropneumoniae serotype-1 were selected. Five pigs/litter were selected at random and were identified (group 1). Blood samples were obtained from group-1 pigs at 2 to 4, 14, 28, 42, and 56 days of age. Blood also was obtained from group-1 pigs remaining in the postweaning unit at 70 days of age, and from 20 to 40 sows 1 to 3 times. To determine prevalence of seropositive pigs in all age groups for the entire study period in herds C to G, blood samples were obtained from 20 pigs/age group (group 2) selected at random at 28, 42, and 56 days of age at each visit. Group-1 pigs were included when they reached 28, 42, and 56 days of age. Pigs were serologically monitored in herds A and B for 3 months and in herds C to G for 5 to 6 months. Serologic status of pigs at 2 to 4 days of age was not statistically associated with status at 42 days (P = 0.6293) and at 56 days (P = 0.3098) of age for the same pigs. Therefore, seronegative pigs 2 to 4 days old did not seroconvert earlier than did those with detectable maternal antibodies at 2 to 4 days old. Only about 50% of the 70-day-old pigs were seropositive at 56 days. Seemingly, pigs seroconverted late in the postweaning period.(ABSTRACT TRUNCATED AT 250 WORDS)