Correlations in the results of virus neutralization test, hemagglutination inhibition test, and enzyme-linked immunosorbent assay to determine infectious bronchitis virus vaccine potency

Abstract

Abstract:The virus neutralization (VN) test was used to determine potency of the infectious bronchitis (IB) vaccine. The results of VN, hemagglutination inhibition (HI), and enzyme-linked immunosorbent assay (ELISA) were compared with those of the IBV M41. The r 2 values between VN and HI titers and the ELISA antibody titer were 0.8782 and 0.0336, respectively, indicating a high correlation between VN and HI, but not VN and ELISA. The Cohen's kappa coefficient between the VN titer of 2 log 10 and HI titer of 5 log 2 was 0.909. Our results showed that VN could be replaced with HI for testing the potency of IBV M41. Keywords: Massachusetts 41 vaccine, hemagglutination inhibition, infectious bronchitis, potency testInfectious bronchitis (IB) causes a highly contagious, acute respiratory disease in chickens [8]. High mortality rates from this bronchitis (especially nephropathogenic IB) may occur in young chicks. However, more substantial economic losses result from a drop in egg production and quality in laying hens with IB and growth retardation and rejection of broilers with IB during processing. IB virus (IBV), the pathogen that causes this disease, belongs to group III of the genus Coronavirus in the Coronaviridae family [14]. It is an enveloped virus containing an unsegmented, positive-sense, single-stranded RNA genome of approximately 27.6 kb [7]. The virion has four major structural proteins, including the nucleocapsid (N) protein, envelope (E) protein, membrane (M) glycoprotein, and spike (S) glycoprotein. The S glycoprotein is post-translationally cleaved into the S1 and S2 subunits [6], with the S1 subunit, located on the outside of the virion, containing virus neutralization (VN) and serotype-specific epitopes and conferring hemagglutination (HA) activity. Thus, S1 induces antibodies involved in VN and hemagglutination inhibition (HI) in the IBV host.The severity of IB depends on many factors, including the strain of the virus and the age, nutrition, and rearing environment of the chicken affected. The pathogen is highly contagious and ubiquitous in most of the world; thus, it is difficult to keep chickens free of IBV, especially in areas where biosecurity is insufficient. Consequently, vaccination using live attenuated and/or inactivated vaccines has been used to control IBV for several decades. Although numerous vaccine strains are available, Massachusetts-type strains, including M41 and H120, have been widely used in immunizations across the world [5,13].Several serological tests are routinely employed for antibody detection. These include the VN test, HI assay, and enzyme-linked immunosorbent assay (ELISA) [10,11]. In addition, these methods have been employed to assess the potency of vaccines. The VN test is the gold standard for testing of vaccine potency. The HI test, another serological assay, has also been used to test IBV vaccine potency in many countries, including the USA, Europe, Japan and some Asian countries. However, in Korea, the HI test is still not used for potency testing of IBV vaccin...