Early serological responses to Mycoplasma hyopneumoniae infection.

A complement fixation (CF) test for Mycoplasma hyopneumoniae antibody, using the complement dilution method, will detect infection in inoculated pigs at an early stage. The interval between inoculation and the first positive CF response--defined as 4.6 u of complement fixed--was determined for four separate methods of inoculation and for pigs with artificially induced pneumonia. Sera from two groups were tested by the enzyme-linked immunosorbent assay (ELISA). By CF, the i.v. group showed positive titers at 9.8 +/- 0.4 (mean +/- SE) days. All pigs in this group had positive titers, most of them at the maximum level of 31 u fixed. The i.p. group first showed positive titers at 13.3 +/- 1.0; 17 of 70 had no CF response. The s.c. group first showed titers at 21.1 +/- 2.6; 7 of 24 did not respond. Intranasal inoculation first produced a CF response at 14.3 +/- 0.9, and all pigs had positive titers. Pigs in contact with those with induced pneumonia first showed titers at a mean of 27.2 days (SE +/- 1.3), and all pigs exhibited a CF response. There was no significant difference between the CF test and ELISA results.