NONSPECIFIC SEROREACTIONS AGAINST BRUCELLA-ABORTUS IN RUMINANTS IN NEW-ZEALAND AND THE PRESENCE OF YERSINIA-ENTEROCOLITICA-0 9/

The level of non-specific reactions found in the brucellosis serology of ruminants in New Zealand was very low until July 1992. This changed when, in an export consignment of 1071 deer, 35% reacted in the Bruce lla abortus tube agglutination test with titres varying from 50 to 200 IU. The reactors were also positive in the Rose-Bengal agglutination test and most of them reacted in the complement fixation test with tit res varying from 10 to 80 IU. Yersinia enterocolitica 0:9 was later is olated from one deer of this consignment. It was the first isolate of this serotype recovered in New Zealand from an animal. Shortly after, false reactors occurred more frequently than before in sera from Bruce lla abortus accredited free cattle herds. As the involvement of Yersin ia enterocolitica 0:9 was suspected in these cases, faecal samples fro m reactors and in-contact animals were cultured for this organism. Yer sinia enterocolitica 0:9 was isolated from nine of 19 herds showing on e or more false Brucella abortus seroreactions. Prior to 1990, Yersini a enterocolitica serotype 0:9 had not been isolated in New Zealand, de spite the recovery of a number of other bio- or serotypes of the organ ism from humans and animals. From 1990 onward, serotype 0:9 began to b e isolated from human faecal samples with increasing frequency. Since the first isolations from deer and cattle in 1992, it has now also bee n recovered from a cat and an alpaca and from cattle without any assoc iation with false positive Brucella abortus reactions. All serotype 0: 9 isolates were of biotype 2.