Rapid heat-treatment attenuation of infectious bronchitis virus

Abstract

In the present study we describe the rapid development of an attenuated live vaccine for GA08, a new serotype of infectious bronchitis virus, using a heat-treatment method. Incubation of the GA08 strain of IBV at 568C and passage in embryonated eggs was used as a method to fast track the attenuation process. The virus was incubated in a 568C water bath and aliquots were removed every 5 min for up to 1 h, and then each aliquot was inoculated into 10-day-old embryonated eggs. Virus with the longest incubation time that produced lesions in the embryos was harvested, again incubated at 568C as described and passaged in embryonated eggs. Attenuation of the virus, designated GA08/GA08HSp16/08, was verified in 1-day-old specific pathogen free chicks. A 10x dose of the vaccine was found to be safe for 2-week-old broiler chicks of commercial origin. The efficacy of the heat-treated attenuated virus was determined by vaccinating broiler chicks of commercial origin at 1 and 14 days of age intraocularly/intranasally. Vaccinated birds that were challenged with 10 4.5 median embryo infectious doses of pathogenic GA08 virus/bird at 28 days of age were protected from the disease, and challenge virus was only detected in the trachea of one of 21 birds by realtime reverse transcriptase-polymerase chain reaction at 5 days post challenge. The attenuation process took 10 weeks to complete, which is a substantially shorter time than required to attenuate infectious bronchitis virus by serial passage in embryonated eggs without heat treatment (38 weeks or more).

Infectious Bronchitis

“…Live vaccines are used in meat type (broiler) chickens and for the initial vaccination and priming of breeders and layer pullets. Infectious bronchitis virus strains used for live vaccines are attenuated by serial passage in embryonating chicken eggs (17), sometimes in combination with heat treatment (99). Evidence that some vaccines increased in virulence after back-passage in chickens (91) demonstrates the potential for enhancement of virulence of such vaccines by contin-ued circulation of the vaccine virus, a rolling infection, in a flock that is often caused by poor vaccination procedure, resulting in vaccination of only a fraction of birds in the house.…”

Successful cross-protective efficacy induced by heat-adapted live attenuated nephropathogenic infectious bronchitis virus derived from a natural recombinant strain

“…The initial selection of the K40/09 virus for this purpose was guided by the fact that this strain has a favored vaccine candidate background that contains two genetically characterized nephropathogenic strains (KM91 and QXIBV) as a recombinant strain [22] and showed significantly high levels of immunogenicity and protective ability against many different types of IBV [11]. Our approach to heat-adapting IBV differed in two ways from previous attempts [13]. Differences included the viral strain (nephropathogenic IBV strain) and the number of passages at high temperature (up to 50 times).…”

“…The development of a temperature-adapted vaccine has been attempted to increase safety and shorten the time of attenuation in several studies [12][13][14]. However, our experience shows that, besides desirable levels of attenuation and immunogenicity, other traits such as good growth properties should also be considered for live vaccine strains, and that this attenuation process may not work for all viruses.…”

Complete Genome Sequence of Avian Coronavirus Strain GA08 (GI-27 Lineage)

“…Since the first identification of IBV in the 1930s in the United States, more than 20 different serotypes and variants have been identified worldwide (4,5). In 2007 and 2008, an outbreak of bronchitis in broilers in North Georgia led to the identification of a new IBV strain designated GA08, which was further classified into the separate lineage GI-27 (6,7). The GA08 IBV strain has since been isolated on farms in Alabama, Tennessee, and Kentucky (8; https://quickvet.net/news-and-media/zoetis-receives-usda-conditional -license-for-first-vaccine-to-control-georgia-08-strain-of-infectious-bronchitis -virus-in-poultr.aspx).…”

“…Over the past years, its incidence and severity have increased dramatically, resulting in significant losses. To date, only partial genomes of the GA08 strain viruses are available in public databases (6,7). In this study, we report the complete sequence of the IBV GA08 strain.…”