Abstract
Egyptian poultry suffer from frequent respiratory disease outbreaks associated with Infectious Bronchitis Virus (IBV) variant 2 strains (Egy/VarII). Different vaccination programs using imported vaccines have failed to protect the flocks from field challenge. Recent studies confirmed a successful protection using homologous strains as live attenuated vaccines. In this study, a newly developed live attenuated IB-VAR2 vaccine representing the GI-23 Middle East IBV lineage was evaluated in day-old commercial broilers in an IBV-endemic area. A commercial broiler flock was vaccinated with the IB-VAR2 vaccine at day-old age followed by IB-H120 at day 16. The vaccinated flock was monitored on a weekly basis till the slaughter age. The health status and growth performance were monitored, and selected viral pathogen real-time RT-PCR (rRT-PCR) detection was conducted on a weekly basis. Finally, the flock was compared to a nearby farm with only the classical IB-H120 vaccination program. Results showed that the IB-VAR2 vaccine was tolerable in day-old broiler chicks. The IBV virus rRT-PCR detection was limited to the trachea as compared to its nephropathogenic parent virus. Respiratory disease problems and high mortalities were reported in the IB-H120-only vaccinated flock. An exposure to a wild-type Egy/VarII strain was confirmed in both flocks as indicated by partial IBV S1 gene sequence. Even though the IB-VAR2-vaccinated flock performance was better than the flock that received only IB-H120, the IBV ELISA (enzyme-linked immunosorbent assay) and log2 Haemagglutination inhibition (HI) antibody mean titers remained high (3128 ± 2713 and ≥9 log2, respectively) until the 28th day of age. The current study demonstrates the safety and effectiveness of IB-VAR2 as a live attenuated vaccine in day-old commercial broilers. Also, the combination of IB-VAR2 and classical IBV vaccines confers a broader protective immune response against IBV in endemic areas.
Highlights
Infectious bronchitis virus (IBV) is a single-stranded enveloped RNA virus that belongs to the genus Gammacoronavirus, family Coronaviridae [1]
Farm 1’s total sold weight was 12,250 kg with a food conversion rate (FCR) of 1.7, while farm 2 yielded a total of 8150 kg with a FCR of 2.1 (Table 2)
The results revealed that a wild-type virulent IBV variant 2 strain was implicated in this outbreak
Summary
Infectious bronchitis virus (IBV) is a single-stranded enveloped RNA virus that belongs to the genus Gammacoronavirus, family Coronaviridae [1]. The virus causes a clinical disease characterized by coughing, sneezing, tracheal rales, and watery eyes. In layer and breeder chickens, the disease is associated with both quantity and quality deterioration of egg production. In Egypt, Massachusetts D3128, D274, D08880, 793B, variant 1 and 2 strains [3,4], and IS/1494/06 nephropathic IBV strain are frequently isolated from poultry [5]. Studies classified recent IBV strains into Egyptian variant 1 (Egy/VarI) and Egyptian variant 2 (Egy/VarII) based on the S1 hypervariable region 3 sequence analysis [4,6]. The IBV variant 2 is the most predominant serotype in
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