Survey of trichinosis in breeding and cull swine, using an enzyme-linked immunosorbent assay

Serum samples obtained from 40,927 swine at various locations in North Carolina between Aug 1, 1987 and July 31, 1988, were tested for antibodies to Trichinella spiralis, using an ELISA based on a larval T spiralis excretory-secretory antigen. In the ELISA, samples were considered to have positive results if the optical density (OD) reading was equal to or 5 times greater than the mean OD value of 4 negative-control sera from trichina-free swine. Of the 40,927 serum samples tested, 154 (0.38%) were positive by ELISA; the rate for breeding swine was 0.35% (105/30,162), and the rate for cull swine was 0.45% (49/10,765). Of the 49 seropositive samples from cull swine, 11 were from out of the state, 22 had no identification, and 16 were known to originate from North Carolina. Seropositivity had a bimodally seasonal distribution, with peaks in March and September. There was no difference between the mean age of seropositive and seronegative swine, but males were at greater risk for seropositivity than were females. Pigs from lots with less than 100 sera tested were at increased risk for seropositivity, as were pigs from the central coastal region of North Carolina.