Infectious Bronchitis Virus Variants in Europe
Infectious bronchitis continues to be one of the major pathogens of chickens throughout Europe, causing disease of economic and welfare importance in chickens of all ages. In fact it is probably endemic in all regions where poultry are reared intensively.
Despite the availability of high quality vaccines, IB continues to be a problem in most regions of Europe. One of the main reasons for this is the continual emergence of new variants of the virus. The prevalence of IB variants in Europe has been recognised as a problem at least since the 1960s, following the emergence of variants such as D207 (D274) and D212 (D1466) in the Netherlands. In the early 1990s, a major new variant 4/91 (also called 793B) was recognised in Europe. This variant, against which a live attenuated vaccine was developed by MSD Animal Health, has continued to be a major pathogen throughout Europe and also in other parts of the world. Whilst 4/91 continues to be a cause for concern in much of Europe, and according to a recent survey, is still the dominant IB variant found in France, two other IB variants, “Italian‐02” and QX, have emerged in Europe in recent years.
Infectious bronchitis virus variant Italian‐02
In the late 1990s a series of IBV strains isolated in Italy were studied closely. The sequence analysis of one of these, designated “Italian‐02”, was published in 2002 (NCBI‐BLAST, number AJ457137). Later on it was found that one of these isolates, called Italian‐O2, had become widespread in Europe. In the early 2000s, in a study carried out using the RT‐PCR technique, it was found to be one of the most predominant genotypes in many countries (Worthington KC et al, 2004). Nevertheless, the importance of “Italian-02” as a major pathogen for poultry has never been confirmed. This is because the studies so far performed have simply detected the virus genome, few virus isolates have been obtained and so it has not been proved that this IBV strain is pathogenic in chickens in the field. Furthermore, in a recent survey (Worthington, KC et al, 2008) “Italian‐02” has been detected less commonly in most countries. The exception to this is in Spain, where it continues to be the dominant type detected (Dolz R et al. 2007).
Infectious bronchitis virus variant D388 (QX)
Since 2004, severe egg production problems have been reported in The Netherlands. Also respiratory signs have been reported in broilers older than 4 weeks of age. In birds in production the problems are characterized by a low production rate with peak levels reaching only between 30% to 55% in apparently healthy flocks. These cases were associated to earlier outbreaks of nephropathogenic infectious bronchitis that had occurred in 2003 in broilers and pullets from which an unidentified variant IB virus was isolated. This original isolate was similar to a Chinese isolate known as QX. The Dutch isolate was later named D388 by the Animal Health Service at Deventer in the Netherlands.