Commercial vaccines used in China do not protect against a novel infectious bursal disease virus variant isolated in Fujian.

BACKGROUND: Since 2018, atrophy of the bursa has been found among vaccinated chickens with high antibody titres against infectious bursal disease virus (IBDV) in Fujian, China, suggesting poor vaccine efficacy against circulating IBDV strains. METHODS: Novel IBDV strains were isolated, and vp2 and vp1 genes were sequenced and used to carry out phylogenetic analysis. Pathogenicity was investigated using 21-day-old specific pathogen-free (SPF) chickens. In addition, the effectiveness of current commercial vaccines used in China was evaluated against the isolated novel IBDV strains. RESULTS: Six IBDV isolates were successfully obtained, which formed an independent cluster and belonged to genotype A2dB1, based on phylogenetic analysis of the vp2 and vp1 genes. The pathogenicity of the novel IBDV FJ2019-01 isolate in 21-day-old SPF chickens was characterised by severe atrophy of the bursa and a largely decreased number of lymphocytes, atrophy of the follicle and broadening of mesenchyme in the bursa 3-23 days after infection. Unfortunately, all vaccinated chickens with high antibody titres against IBDV also developed atrophy and largely decreased lymphocytes in the bursa, as in the unvaccinated birds challenged with FJ2019-01. Furthermore, high viral loads of FJ2019-01 were detected in the bursa of all vaccinated chickens. CONCLUSIONS: These findings suggest that current commercial IBDV vaccines used in China did not provide protection against novel IBDV variants.

Genetic and pathogenic characteristics of a novel infectious bronchitis virus strain in genogroup VI (CK/CH/FJ/202005).

Infectious bronchitis virus (IBV) has a significant impact on the poultry industry, and genogroup VI (GVI) IBVs, such as the TC07-2 strain, were reported in China since 2007. We isolated a novel strain, CK/CH/FJ/202005 (henceforth 202005), from broilers that were vaccinated with different attenuated IBV strains (H120, 4/91, or QX) in Fujian, China during 2020. Based on comparison with the SNU8065 strain (GI-22), the 1ab genes were the locations of recombination in this new isolate. Pathogenicity testing of 1-day-old and 15-day-old specific pathogen-free (SPF) chickens indicated varying severities of air sacculitis beginning 5 days-post-inoculation (DPI). Histopathological analysis indicated that tracheal lesions started at 5 DPI and persisted throughout the 30-day experiments in 1-day-old infected chickens. Virus re-isolation and viral load tests indicated this strain was mainly in the trachea, and not the kidneys. Our findings showed that the 202005 strain was pathogenic in 1-day-old and 15-day-old chickens. These results should be considered when developing strategies to control IBV infections.