Virulent Avian Infectious Bronchitis Virus, People’s Republic of China

Jinling Feng, Yanxin Hu, Zhijun Ma, Qi Yu, Jixun Zhao, Xiaodong Liu, and Guozhong Zhang

Author affiliations: Author affiliations: The Key Laboratory of Animal Epidemiology and Zoonosis, Ministry of Agriculture, China Agricultural University, Beijing, People’s Republic of China (J.L. Feng, Y.X. Hu, J.X. Zhao, G.Z. Zhang); Animal Husbandry and Veterinary Station of Beijing, Beijing (Z.J. Ma, Q. Yu, X.D. Liu)

Abstract

A virulent avian infectious bronchitis virus (IBV) was isolated from 30-day-old broiler chickens that exhibited respiratory symptoms, nephropathologic lesions, and a high proportion of deaths in the People’s Republic of China during 2005. The strain, designated YN, was genetically and pathologically characterized. Phylogenetic analysis showed that YN and most of the previously characterized IBV isolates found in China were phylogenetically classified into 2 main genetic clusters. The YN isolate caused severe lesions and resulted in deaths of 65% in experimental infections of 30-day-old specific-pathogen–free chickens. Tracheal and severe kidney lesions developed in all infected birds, confirming the ability of YN strain to induce both respiratory and renal disease. IBV antigens were detected by immunohistochemical analysis in the trachea, lung, kidney, and bursa, consistent with histopathologic observations, virus isolation, and reverse transcription PCR detection. We showed that YN IBV exhibits severe pathogenicity in chickens, and that similar viruses are prevalent in China.

Avian infectious bronchitis virus (IBV), a member of family Coronaviridae, order Nidovirales, causes a highly contagious respiratory and sometimes urogenital disease of chickens that is characterized by respiratory signs, nephritis, or reduced egg production and quality in layer chickens. IBV is a major poultry pathogen that is endemic worldwide and leads to serious economic losses.
The main method of protecting poultry from infectious bronchitis (IB) is the administration of live or killed vaccines. However, IB continues to cause economic losses in the poultry industry despite intensive vaccination programs in many countries (1–5). Outbreaks of IB often are due to infections with strains serologically different from those used for vaccination (2,6). Since IBV was first described in 1931, a large number of serotypes or variants have emerged, and some have become endemic worldwide (4,7–12). That little or no cross-protection occurs between different serotypes of IBV is well known (13). Therefore, continuous determination of the epidemic serotype and production of new generations of vaccines are crucial for controlling IB in each geographic region or country.
IBV was first isolated in the People’s Republic of China in the early 1980s; since then, the Massachusetts-type (e.g., H120, H52, Ma5, W93, and 28/86) or Connecticut-type live attenuated IB vaccines and the inactivated killed oil-emulsion vaccine have been used to prevent and control the disease. However, the serotypes of the vaccines used have been epidemiologically determined to differ from those of the predominant IBV isolates in China that form 2 large groups of unique strains, named A2-like and QXIBV-like strains (5,6,14–18). Therefore, because of the lack of a vaccine against endemic strains of IBV in China, IBV infection has remained a problem in the Chinese poultry industry.
We isolated a virulent IBV strain from 30-day-old broiler chickens in the Yunnan Province and characterized it using sequence alignment, phylogenetic analysis, pathogenicity studies, histopathologic observation, and immunohistochemical (IHC) examination. The results indicate that the isolate is genetically similar to most of the prevalent strains of IBV found in China. We also showed that IBV YN isolate displays more severe pathogenicity than previously characterized strains in China.