Infectious bronchitis virus testing update
Davor Ojkic, Marina Brash, Emily Martin, Emily Brouwer
The number of samples submitted to the Animal Health Laboratory for infectious bronchitis virus (IBV) testing has increased significantly over the last 10 years (Fig. 1). Intensified testing began with incursion of variant IBVs into Ontario’s commercial chicken flocks of various commodities in 2012 and 2013, with IBV 4/91 the most frequently detected IBV strain (Fig. 2) at that time. This strain was reported to be endemic in Europe, Africa and Asia, and at this time is also present in Quebec, but has still not been reported in the USA.
As other variant strains were introduced into Ontario chicken flocks, the demand for IBV testing continued to climb, reaching almost 1,800 samples in 2018. Consequently, the number of requests for IBV genotyping also increased, peaking at > 300 samples genotyped in 2017 and 2018 (Fig. 1). In 2015, the number of IBV 4/91 infected flocks was trending downward, but IBV re-emerged in late 2015 causing high production losses in Ontario poultry flocks. With genotyping, a new IBV strain related to a strain DMV/1639/11, first detected in 2011 in broiler flocks on the Delmarva (DMV) peninsula, was identified in Ontario (Fig. 2). In early 2019, this IBV strain continues to be identified in commercial flocks, however the clinical impact has been reduced through the implementation of novel vaccination strategies using existing IBV vaccines in conjunction with good management and heightened biosecurity.
In addition to the IBV 4/91 and DMV strains, US variant strains including California 1737/04 and Pennsylvania Wolg/98 also continue to circulate in Ontario and are associated with production losses and elevated mortality but at a lower frequency. PA/Wolg was first detected in Ontario in 2000-2002 and CA/1727/04 in early 2012.
The ability to genotype IBV strains is critical to the management of this disease given that multiple strains are circulating at any one time in the province and, based on Ontario’s track record, there is always a risk of new incursions. AHL
Figure 1. Number of samples tested for IBV by PCR and genotyped at the AHL from 2009-2018.
Figure 2. Genotypes of IBVs detected at the AHL from 2012-2018.