Infectious bronchitis viruses (IBVs) circulating in Malaysia are classified into two groups as Malaysian QX-like and variant strains. In this study, the pathogenicity of IBS130/2015 (QX-like) and IBS037A/2014 (variant) IBVs in 1-day-old and 30-day-old specific pathogen free (SPF) chickens was characterized. Both strains caused respiratory and kidney infections based on immunohistochemistry (IHC), real-time quantitative polymerase chain reaction (qPCR) and a ciliostasis study; however, the results showed that the QX-like strain was more pathogenic, caused higher mortality and showed higher tissue tropism for the kidney than the variant strain. In contrast, despite causing low or no mortality depending on the age of the infected chickens, the Malaysian variant strain showed high tissue tropism for the respiratory tract compared with the QX-like strain. IHC and qPCR indicated the presence of both IBV strains in the epithelial lining of villi in the jejunum and the caecal tonsil; however, no pathological changes were detected in these organs. Both the Malaysian QX-like and variant IBV strains are able to infect the respiratory tract and kidney of chickens irrespective of age.
Besides the vaccine strains, the Malaysian variant (MV) and QX-like are the predominant IBVs detected on commercial poultry farms. These two virus strains are distinct based on genomic and pathogenicity studies. In this study, we determined the sequence of the S1 gene and compared the pathogenicity of serial passage 70 (P70) of Malaysian QX-like (QX/P70) and MV (MV/P70) strains with that of their respective wild-type viruses. The nucleotide and amino acid sequences of the complete S1 genes of QX/P70 and MV/P70 showed 1.4 to 1.6% and 3.0 to 3.3% variation, respectively, when compared to the wild-type virus. Most of the mutations were insertions and substitutions in the hypervariable regions (HVRs), primarily in HVR 3. Furthermore, selection pressure analysis showed that both viruses are under purifying selection. A pathogenicity study in specific-pathogen-free (SPF) chickens showed a reduction in respiratory and kidney lesions in chickens inoculated with MV/P70, but not with QX/P70, when compared to the respective wild-type viruses. However, MV/P70 is still pathogenic and can cause ciliary damage. In conclusion, the MV IBV strain is more responsive than the QX-like IBV strain following the attenuation process used for the development of a live attenuated IBV vaccine.
Infectious bronchitis virus (IBV) infection is highly infectious respiratory disease in poultry industry with significant economic importance. The prevalence of IBV in quail industry in Malaysia was not well documented; therefore, its actual role in the epidemiology of the disease is relatively unknown. This study was to determine the susceptibility of Japanese quail, as one of the species in commercial poultry industry, toward IBV. In addition, it will also give a potential impact on the overall health management in the quail industry even though it had been established that quail are resistant to diseases affecting poultry. Moreover, to the best of our knowledge, it is the first experimental study on IBV inoculation in quail. In this experimental study, 20 quails were divided into 4 groups (n = 5 for group A, B, and C, n = 5 for control group). The quails in group A, B, and C were infected via intraocular and intranasal routes with 0.2 mL of 10 × 5 EID50 of the virus. Clinical signs, gross lesions, positive detection of virus, and trachea histopathological scoring were used to assess the susceptibility of these Japanese quails. The results have indicated mild ruffled feathers and watery feces in these inoculated birds. Trachea, lung, and kidney were subjected to one-step reverse transcription polymerase chain reaction for virus detection. The virus was found from trachea and lung samples, whereas it was absent from all kidney samples. Only 3 quails were found with gross lesions. There was a significant difference of tracheal lesion by 0.009 ± 0.845 (P < 0.05) within the treatment groups. In summary, Japanese quails might be susceptible to IBV.