[Season-related incidence of Yersinia enterocolitica in fecal material of healthy slaughterhouse pigs (author's transl)].

In the period July 1976 to June 1977 a total of 1358 fecal specimens and 165 mesenteric lymphnodes of healthy slaughterhouse pigs were examined for Yersinia enterocolitica (Y.e.). The animals originated from 215 farms in 86 localities of Northern Bavaria. Y.e. was found in fecal specimens of 371 pigs (27.3%). A total of 408 strains was isolated including 35 double and one triple infections. Most cultures belonged to serogroups O:6...(186 strains), O:7...(78 strains), and O:5...(71 strains, Table 3). The serogroups O:3 and O:9 which in Europe are most frequently associated with human disease were isolated from 26 animals (1.9%). Lymphnodes were positive in two instances only (1.2%). Besides aerobic subculture on SS-agar after cold enrichment in phosphate buffered saline anaerobic incubation was performed simultaneously during the last 8 months of the study. This method rendered more than twice as many isolations due to an effective inhibition of environmental bacteria with oxidative metabolism (mainly Pseudomonas spp.; Tables 3 and 4). The incidence of asymptomatic infections was markedly related to season. The lowest incidence was observed during the summer months (August 1976:0%) but increased steadily to a maximum in April 1977 (71.2%; Table 4). With one exception the serogroups O:3 and O:9 were only isolated during October to December (Fig. 1). Despite the frequent occurrence of Y.e. in healthy pigs the significance of these animals for human yersiniosis remains to be clarified. Especially the frequency of disease in infants and young children would not suggest porc meat as an important vehicle of transmission. It is imaginable that the human pathogenic serogroups O:3 and O:9 might be simultaneously adapted to several hosts with independent cycles of infection. Future investigations will mainly have to consider the elucidation of the hitherto unknown mode of transmission of human yersiniosis.