SEROPREVALENCE AND MOLECULAR CHARACTERISATION ON INFECTIOUS BRONCHITIS VIRUS IN CHICKENS IN SOUTHWESTERN NIGERIA

Abstract

Infectious Bronchitis (IB), a viral respiratory disease of chickens is a major threat to the poultry industry causing decreased egg production. Despite vaccination against the disease, outbreaks continue to occur in Nigeria with clinical features similar to other respiratory diseases. There is limited information on the circulating andavailable vaccine strains in southwestern Nigeria. This study was designed to investigate the level of awareness of farmers, experience of outbreaks by veterinarians, available vaccines and current seroprevalence of IBas well as characterise circulating virus in commercial and local chickens in Lagos, Ogun and Oyo states.

Structured questionnaires were interviewer administered purposively to obtain information on IB awareness from 83, 105 and 96 registered poultry farmers (based on accessibility) as well as experience of outbreak from 56, 64 and 70 veterinarians (based on poultry specialisation) in Lagos, Ogun and Oyo states, respectively, between September and November, 2015. A survey of commercially available IB vaccines was also conducted.Blood, cloacal and oropharyngeal swabs were obtained from 10 chickens per unvaccinated commercial flock from 15 randomly selected poultry farms per state. One hundred similar samples were obtained from unvaccinated local chickens in five locations per state. Cloacal and oropharyngeal swabs, lung and kidney tissues from21dead commercial chickens with history of respiratory signs were obtainedfrom poultry diseases diagnostic centers in the studyarea. Sera were screened for IB virus antibodies using ELISA, while other samples were subjected to reverse transcription polymerase chain reaction for virus detection. Purified 1b, S1 and NP genes were sequenced using Sanger’s method. Nucleotide and amino acid sequences were aligned with sequences retrieved from GenBank using software. Phylogenetic analysis was performed using the Neighbour-Joining method. Data were analysed using descriptive statistics, ANOVA and independent t-test at α0.05.

Among the farmers, only 27.7%, 24.8%, and 28.1% were aware of IB, 22.9%, 19.0% and 24.0% vaccinated their chickens, while 10.8%, 19.0% and 10.4% had experienced outbreaks in Lagos, Ogun and Oyo states, respectively. Among the veterinarians, 28.0%, 37.0% and 30.0% had encountered IB outbreaks, while 72.0%, 55.5% and 66.0% advised farmers to vaccinate in Lagos, Ogun and Oyo states, respectively. Massachusetts strain H120 was the only IB vaccine strain available. Seroprevalence was 83.3%, 88.0% and 76.0% in commercial chickens and 70.0%, 85.0% and 82.0% in local chickens in Lagos, Ogun and Oyo states, respectively. Mean antibody titers were significantly higher in commercial chickens (49.74±2.50 and 43.25±4.64) than in local chickens (24.71±2.02 and 31.85±2.24), respectively, from Lagos and Oyo states. Phylogenetic analysis of the 1b and S1 gene sequences showed that detected IB virus strains clustered with Dutch Strain H120 Variant 2 (Israel) and Italian strain Qx, while analysis of the NP gene revealed 98-99% similarity with South Korean strain K210.

High prevalence of infectious bronchitis among chickens in Lagos, Ogun and Oyo states was established with circulating strains of the virus being genetically diverse from the available vaccine strain. Vaccines for use in southwestern Nigeria should be produced from homologous strains detected.