Despite vaccination against Infectious bronchitis virus (IBV) with the Massachusetts type vaccine viruses H120 and H52 in the Netherlands, an increasing number of properly vaccinated flocks have suffered from the disease since 1978. In the years 1978-1982, the virus was isolated from 162 IBV suspected flocks. Cross-virus-neutralization tests showed that the majority (67 per cent) of these isolates belonged to serotypes other than the Massachusetts type, the Connecticut-, Florida-, Iowa 97-, Iowa 609- and JMK serotype. The majority of these Dutch isolates could be divided into 4 serogroups, called D207, D212, D3128 and D3896. Only a few isolates were not related to these serotypes. A survey of 328 flocks for antibody against these serotypes demonstrated that antibody against one or more of these novel serotypes were present in most of the flocks. Experiments demonstrated that vaccination with the H120 vaccine virus was not able to protect chickens against the adverse effects of a challenge with the novel serotypes.
SUMMARYTwelve Dutch isolates and the M41 strain of infectious bronchitis virus (IBV), a coronavirus of chickens, were characterized by cross-neutralization and T1 fingerprinting to elucidate their evolutionary relationship. The T1 fingerprinting showed that the Dutch isolates formed two clusters. The first cluster contained strains H52, H120, D387, V1259, V1385 and V1397; the estimated sequence homology is 99~. Cluster two comprised strains D207, D274, D212, D1466, D3128 and D3896, which have about 95~ sequence homology. The M41 virus did not belong to either cluster. The four different serotypes which arose in the/ate 1970s belonged to cluster two and appeared to be different from the vaccine strains (H52 and H120) used at that time. This indicates that the strains were newly introduced and could have arisen from a common virus. On the other hand, three recently isolated field strains were genetically closely related to the vaccine strains H 120 and H52 (cluster one), suggesting that these live vaccine strains themselves could have given rise to these serologically altered field isolates. The data are relevant to the development of new vaccine strategies.
The incidence of intestinal spirochaetes was determined using direct fluorescent antibody microscopy on faecal and mucosal samples from chickens. Of 134 flocks with intestinal disorders 27.6% were found to be positive, but only 4.4% (of 45 flocks) were positive where signs of enteritis were absent. Flocks housed in cages or with access to litter were equally affected. No evidence was found for pigs as an aetiological factor.
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