Abstract

Background:
Infectious bronchitis virus (IBV) is an endemic poultry disease in Bogor Regency, West Java Province, Indonesia. This highly contagious disease spreads through direct contact with infected chickens, contaminated feces, virus-laden air, or asymptomatic carriers, such as birds. Among these carriers, pigeons (Columba livia) and spotted doves (Spilopelia chinensis) are commonly kept as pet birds and frequently interact with domesticated chickens, thereby increasing the risk of transmission. The high mutation rate of IBV, which generates numerous variants, further amplifies the risk. IBV can mutate within these asymptomatic carriers when pigeons and spotted doves act as reservoirs. Mutations may facilitate viral evolution and recombination, potentially leading to the emergence of new variants with varying pathogenicity.

Aim:
This study aimed to identify the potential of pigeons and spotted doves as reservoirs of IBV and perform molecular characterization of isolated IBV strains.

Methods:
A total of 7 pigeons and 8 spotted doves, acquired from Bogor Regency bird shops, were divided into four groups by species and observed for 12 weeks at the university animal facility. During this period, cloacal and oropharyngeal swabs were collected every 2 weeks and pooled to streamline analysis. Then, 24 pooled samples were inoculated into three 9-day-old embryonated chicken eggs to facilitate virus isolation. Following the inoculation process, IBV detection was conducted using agar gel precipitation assay, reverse transcription polymerase chain reaction (RT-PCR), and morphological observation of the embryos. In addition, agar gel precipitation (AGP) and RT-PCR were directly performed on the swabs without prior virus isolation to ensure comprehensive detection. RT-PCR targeted the nucleocapsid (N) and untranslated region genes, while the following nested RT-PCR targeted the spike gene (S1). To gain deeper insights into the viral characteristics, PCR products that tested positive for IBV were further analyzed through sequencing.

Results:
No birds showed clinical signs of IBV infection during the observation period. The AGP results showed IBV in direct swab samples collected between weeks 2 and 8. Virus isolation using embryonated chicken eggs extended the detection period, identifying IBV in samples collected from weeks 0 to 12. Similar results were obtained using RT-PCR, but only the S1 gene was successfully detected. Isolated IBV strains caused dwarfing and hemorrhage in embryos. The detected IBV isolates shared a high similarity with IBV 1/96, a 793B-like variant commonly used in disease vaccines, according to sequencing analysis.

Conclusion:
Pigeons and spotted doves may act as reservoirs for IBV, as the disease is detected in their swabs and through isolation in embryonated eggs.
IBV from these isolates not only causes embryonic damage but is also closely related to the IBV 1/96 (793B-like) vaccine strain. The results show the importance of monitoring pigeons and spotted doves as part of comprehensive IBV control strategies.

Key words: Infectious bronchitis virus (IBV); Pigeons; Spotted doves; Reservoir; Molecular characterization.