Survey of Actinobacillus (Haemophilus) pleuropneumoniae infection in swine by different methods

Lung and serum samples from pigs that died or were emergency-slaughtered in a pooled, conventional fattening herd were examined to survey Actinobacillus pleuro-pneumoniae infection and to compare the sensitivity of different testing methods. A total of 110 lungs were used for cultural isolation of the agent and direct immunofluorescence (IF) of impression smears. Boiled lung suspensions were tested by coagglutination (Co-A) and agar gel precipitation (AGP). Eighty-seven sera were tested along with lung samples from the same pigs. The lungs yielded a varied bacterial flora most often containing Pasteurella multocida and less frequently Actinomyces (Corynebacterium) pyogenes, E. coli and Salmonella. A. pleuropneumoniae was isolated from 30 lungs: from 22 lungs it grew out in pure culture, from 7 as mixed culture with P. multocida and from 1 as mixed culture with A. pyogenes. The number of positive samples obtained by the different methods was as follows: coagglutination test (with boiled lung suspensions): 63 (57.3%); immunofluorescence: 43 (39.2%); AGP test (with serum): 31 (35.6%); AFP test (with boiled lung suspension): 25 (22.7%). A total of 23 samples (20.7%) were negative by all serological tests and by cultural isolation. Most samples gave positive results by two or more tests while 26 samples only by one test (most often, on 13 occasions, by the Co-A test). The Co-A test detected antigenic components of serotypes that have not been isolated in Hungary so far. This indicates that it is not enough to test one strain from a given lung sample: several colonies must be cultured and serotyped.(ABSTRACT TRUNCATED AT 250 WORDS)