Variability Assessment of California Infectious Bronchitis Virus Variants

Abstract

On the basis of the data from the California Animal Health and Food Safety Laboratory System, 1444 infectious bronchitis (IB) cases were diagnosed between 1997 and 2012. Epidemiologic analyses demonstrated two major IB virus (IBV) outbreak peaks, affecting mainly 35-to-49-day-old broiler chickens. California variant 1737 (CA1737) and California variant 1999 (Cal 99) IBV types were the most prevalent genotypes during the analyzed period. To further understand the increased prevalence of these genotypes, we assessed and compared the variability of the S1 gene hypervariable region of CA1737 and Cal 99 with the variability of IBV strains belonging to the Massachusetts 41 (M41) and Arkansas (Ark) types during serial passages in embryonated chicken eggs. On the basis of the S1 nonsynonymous changes, seven different subpopulations were detected in M41. However, the predominant population of the field strain M41 before passages continued to be predominant throughout the experiment. In contrast, Ark passaging resulted in the detection of 13 different subpopulations, and the field sequence became extinct after the first passage. In IBV Cal 99, eight different subpopulations were detected; one of these became predominant after the second passage. In CA1737, 10 different subpopulations were detected. The field strain major sequence was not detected after the first passage but reappeared after the second passage and remained at low levels throughout the experiment. Compared with M41 and Ark, Cal 99 and CA1737 showed intermediate variability.

Infectious bronchitis virus variants in chickens: evolution, surveillance, control and prevention

“…At the genomic level, these differences can be greater or equal to 5% in the hypervariable region of the S1 gene. These variant strains are usually restricted to geographic regions and most of the time are transient (Gallardo et al 2016), reason why diagnostics and epidemiological surveillance are crucial to determine their existence and persistence. This strategy helps planning preventative measures in the field.…”

“…ArkDPI vaccines showing higher heterogeneity have been associated with respiratory signs and tracheal damage (Ndegwa et al 2012). Studies in variant IBV variability have shown different levels of heterogeneity in different IBV genotypes (Gallardo et al 2016). It is important to understand the heterogeneity of variant IBV strains before selecting them as vaccine candidates.…”

“…Poor diagnostic and surveillance capabilities are a reality in most Latin American and African countries and, where these tools are available, it is very common to see errors in technique and result interpretation (unpublished data). Accurate diagnosis and targeted surveillance is crucial to adequately prevent and control IBV variant rise and its detrimental effects (Gallardo et al 2016). Other than orienting in the vaccine selection and vaccination strategy, accurate diagnosis will drive efforts to impede variant generation.…”

“…Currently, nearly 100 genotypes have been recognised for causing impact on the commercial poultry industry. Some are restricted to specific geographic areas (Gallardo et al 2016).…”

“…The objective is to test protection elicited by commercially available vaccines. If the protection provided by the available vaccines is not adequate, studies to assess variability of the detected variant should be performed to determine if formulating a homologous vaccine to prevent outbreaks is safe (Gallardo et al 2016). Sometimes IBV variants that are not clearly associated with disease are detected.…”