Development of diagnostic methods and examination of vaccination failures for avian coronavirus infectious bronchitis virus
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Infectious bronchitis virus (IBV) is an avian coronavirus with major economic importance to commercial chicken producers worldwide. Due to the existence of multiple serotypes and variants of the virus that do not cross protect, it is essential to choose the right vaccine types and to establish an optimized vaccine protocol using rapid diagnosis of circulating viruses. Thus, rapid, sensitive and specific diagnostic tests that can distinguish different IBV types are extremely important. In addition, understanding the dynamics of IBV vaccines in poultry flocks where mass vaccine delivery methods are used is also a key to control. In an effort to improve currently used diagnostic tests, a microsphere-based assay was developed and evaluated for simultaneous detection of the five most common IBV serotypes in the USA; Arkansas (Ark), Connecticut (Conn), Massachusetts (Mass), Delaware (DE072), and Georgia 98 (GA98). The microsphere-based assay was highly specific and able to detecte co-infections in clinical samples, which was an advantage over currently used tests. These results demonstrate that the microsphere-based assay is a rapid and accurate diagnostic tool with the potential for high throughput. To understand the dynamics and persistence of Arkansas vaccine, we evaluated vaccine interference in one-day old broilers vaccinated in a spray-cabinet and we examined efficacy of different vaccine application methods. There was no interference between vaccines; rather there was a slight enhancement of protection against the Ark challenge virus when combined with other IBV vaccine types. Our findings suggested that Ark vaccine virus was not providing adequate protection against homologous challenge when it was administrated via spray cabinet or drinking water. Moreover, detection of IBV vaccine virus early after administration (regardless of strain or route) correlated with protection against homologous challenge, which may be a good indicator of vaccine efficacy in the field since humoral antibody titers are typically low or undetectable following vaccination. These experiments provide some key findings that can be used to direct the efforts for improving the efficacy of IBV Ark type vaccines given in the hatchery and are an important step in elucidating the factors contributing to the persistence of Ark vaccine in the field.