EPIDEMIOLOGIC CLASSIFICATION OF INFECTIOUS-BRONCHITIS VIRUS ISOLATED IN KOREA BETWEEN 1986 AND 1997

Forty Korean isolates and four reference strains of infectious bronchi tis virus (IBV) were classified by reverse transcriptase-polymerase ch ain reaction and restriction fragment length polymorphism (RFLP) analy sis. Each Korean isolate was isolated from different types of commerci al chicken flocks between 1986 and 1997, KELP patterns of an amplified DNA fragment (1722 bp) containing the SI gene of IBV digested by rest riction enzyme HaeIII showed that the 40 Korean isolates were classifi ed into five genotypes, I to V. Six of them belonged to genotype I whi ch had the same HaeIII and XcmI cleavage patterns with Massachusetts t ype (H120 and M41) but the other four genotypes had a different HaeIII cleavage pattern from the four reference IBV strains used in this stu dy. Genotype III seemed to be the major type as 29 of the 40 isolates belonged to this type which was consistently found in the chicken floc ks since 1990, On the other hand, genotypes II, IV and V were found in the field only in 1986, 1995 and 1995, respectively. Five isolates se lected from each of the five genotypes were inoculated into 1-day-old specific-pathogen-free chicks to evaluate their pathogenicity. Genotyp e III induced 50% mortality as well as severe renal urate deposition o n the kidneys but the other four genotypes only showed respiratory dis tress at 1 to 2 days after inoculation. Live H120 vaccine protected ch icks against challenge with isolates selected from genotype I, but not genotypes IV to V, A live KM91p120 strain selected from major genotyp e III did protect chicks against challenge with isolates from genotype III, in addition to other genotypes, including two recent isolates of genotypes IV and V.