Abstract
Fifty-four-week-old layer birds exhibiting signs of respiratory distress, greenish diarrhea and drop in egg production were investigated. A marked drop in egg production (55%) was recorded with eggs appearing white and soft-shelled. Post-mortem lesions included cloudy air sacs, frothy and congested lungs with mortality in the range of 1 – 2 %.Viral RNA was extracted from tissue samples (trachea, lungs, spleen and liver) and tested for Avian influenza virus (AIV), Newcastle disease virus (NDV) and Infectious bronchitis virus (IBV) by reverse transcriptase-polymerase chain reaction (RT-PCR). Virus isolation was also attempted in 9-11 day-old embryonating chicken eggs (ECE). In order to determine prevalence of IBV serotype(s) in the flock, serum samples were screened by haemagglutination-inhibition (HI) test using IBV antigens and antisera (Arkansas, Connecticut, and Massachusetts).
Neither AIV nor NDV but IBV was detected in the tissue samples by RT-PCR. In addition, virus isolate obtained after four serial passages in ECE produced dwarfed, stunted and haemorrhagic embryos, and the isolate was confirmed by RT-PCR to be IBV. The serum samples were 100% seropositive for three serotypes with HI titres ranging from 5 to 12 Log2.
In this study, Infectious bronchitis was confirmed as the causative agent of observed respiratory distress and drop in egg production. Evidence of co-circulation of multiple IBV serotypes is to the best of our knowledge the first of such report in Nigeria. We recommend extensive molecular and sero-epidemiology of circulating IBV genotypes and serotypes in Nigeria with the aim of developing better control strategies including vaccination.

Key words: Infectious bronchitis, Virus isolation, Molecular detection, Serotypes, drop in egg production, Respiratory distress