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A panel of three anti-glycoprotein 5 (gp5) protein monoclonal antibodies (mAbs) (15, 28 and 246) and three anti-nucleocapsid (N) protein mAbs (SDOW17, VO17 and EP147) was used to investigate, by an indirect fluorescent antibody test, the antigenic variations of 50 Korean isolates of porcine reproductive and respiratory syndrome virus (PRRSV), and compare them with a us ATCC vR2332-derived attenuated vaccine strain and the reference European Lelystad strain of PRRSV. A multiplex PCR assay for the differentiation of European and North American genotypes of PRRSV was used to determine the genotype of the 50 Korean isolates. Forty-six (92 per cent) of the 50 Korean isolates shared the epitopes recognised by the anti-N protein mAb SDOW17. No reactivity to the anti-gp5 and anti-N protein mAbs was observed with the other four isolates. Six distinct patterns could be identified on the basis of their reactivities with the anti-PRRSV mAbs. All 50 isolates were identified as North American genotypes by the differential PCR.

A retrospective study was made of natural infections with Isospora suis in nursing piglets, recorded from April 1994 to May 1997, to determine the prevalence, microscopical lesions and other microorganisms associated with coccidiosis. One hundred and five (17.3 per cent) of the 605 nursing piglets submitted from 304 pig farms were diagnosed positive for coccidiosis. The affected piglets were from seven to 20 days old, with a mean age of 11.1 days. Coccidiosis occurred in each year but the incidence peaked in July (15 cases, 14.3 per cent), September (15 cases, 14.3 per cent), October (16 cases, 15.2 per cent) and November (18 cases, 17.1 per cent) and was lowest in May (no cases), August (two cases, 1.9 per cent) and June (four cases, 3.8 per cent). Histopathologically, villous atrophy resulting from the necrosis and sloughing of epithelial cells was a prominent feature of infection with I suis. In 49.5 per cent of the nursing piglets, other enteropathogens were identified, Escherichia coli (47.6 per cent) and transmissible gastroenteritis virus (3.8 per cent) being the most commonly diagnosed. Forty-five of 50 E coli isolates associated with coccidiosis tested negative by polymerase chain reaction for enterotoxigenic virulence factors, such as fimbriae and enterotoxins.