Detection of infectious bronchitis virus strains similar to Japan in Taiwan

TSAI, Cheng-Ta; TSAI, Hsin-Fu; WANG, Ching-Ho

The one-direction neutralization tests were performed using a constant virus-constant antiserum procedure as described previously [15] . The antisera used for this test included anti-TW-I, anti-TW-II and anti-Mass (Charles River Lab, North Franklin, CT, U.S.A.) [4] . Briefly, 100 µl of virus (containing 100 50% viral embryo infectious doses) was incubated with 100 µl of antiserum (containing 20 units) at room temperature for 1 hr. The infectivity of the virusantiserum mixture was assayed in 10 9-to-11-day-old SPF chicken embryos. After 1 week, embryos were evaluated for IBV infection by observing for death, dwarfing and urate deposition as described for virus titration. In the control groups, antisera were replaced with PBS. A virus was considered to match the serotype of the antiserum, if the antiserum protected five or more of the embryos. The results showed that the two new IBV isolates similar to Japan, S78 and TC3, were not neutralized completely with the reference antisera. The protection rates for S78 by anti-TW-I, anti-TW-II and anti-Mass were 0/10 (numbers protected/ numbers tested), 0/10 and 0/10, respectively. Those for TC3 were 1/10, 4/10 and 0/10, respectively. The results indicated that both viruses could not be neutralized by reference antisera, since their protection rates were less than 50%. Despite extensive vaccination, IB has occurred occasionally, especially in cold seasons. Most IBVs present in Taiwan are TW-I or TW-II. Surprisingly, in the present study, TW-II was more predominant than TW-I, contrary to previous reports [5, [7] [8] [9] . Furthermore, a challenging aspect of this investigation was the emergence of new types, such as the IBVs similar to strains isolated in Japan, which were found to be widespread in Taiwan since they were identified in different locations and different chicken breeds. A previous study revealed that five genotypes existed in Japan in 2010, JP-I, JP-II, JP-III, 4/91 and Mass [1] . In the present study, the IBVs that were similar to Japanese strains showed the highest similarity to JP-I. However, the origin of these isolates is unknown and needs further investigation. The current vaccine strains might not protect against these new isolates, since the one-direction neutralization tests showed less than 50% protection in chicken embryos.