Serological studies in pigs with Mycoplasma hyopneumoniae

Abstract

Further work is described on the complement-fixation (CF) test for Mycoplasma hyopneumoniae infection in pigs, using unheated pig serum. Young pigs, 7 weeks old, were more susceptible than older pigs to M. hyopneumoniae infection; they developed lung lesions and a positive CF reaction. Three out of eight 14-week-old pigs inoculated with M. hyopneumoniae did not produce a positive M. hyopneumoniae CF reaction. Serum samples from M. hyorhinis infected pigs produced slight reactions in the M. hyopneumoniae CF test. The CF reactions between sera from M. hyorhinis infected pigs and M. hyopneumoniae antigen were greater if lung lesions were present in the pig. The possible nature of these cross-reactions and the specificity of the test is discussed. One hundred and twenty five samples from the laboratory herd gave negative results in the M. hyopneumoniae CF test. Heating the pig serum had the effect of substantially decreasing the CF titres and the addition of 1 50 normal serum from day-old pigs did not fully restore the titres. Formalin had the effect of reducing and often eliminating the CF titres of both heated and unheated serum samples. Using gel diffusion studies M. hyopneumoniae antigen could not be detected in diseased lungs resulting from M. hyopneumoniae infection. A slide agglutination reaction could not be demonstrated using serum samples from M. hyopneumoniae infected pigs. The CF test showed that the strains of M. hyopneumoniae, 11, 6238, M244, EP29 and EP33, were antigenically similar. Cross-reactions occurred in the CF test between M. hyorhinis antigen and M. hyopneumoniae immune rabbit serum. Using gel diffusion studies these cross-reactions were shown to be due to adsorption of medium constituents by organisms when grown in broth. The immune rabbit serum contained antibodies to the medium's constituents.