Re-current Epizootics of Highly Pathogenic Avian Influenza in Nigeria: Status of Vaccination as Alternate control

Abstract

Epizootic of Highly Pathogenic Avian Influenza subtype H5N1 in Nigeria was successfully contained during the first wave that lasted from 2006 to 2008 without the use of vaccine. Re-current and more severe outbreak was witnessed in 2015 and there are suspicions that some farmers may have resorted to vaccination to prevent infections in their flocks. We investigate evidence of vaccination in farms and the status of vaccination as alternate control for HPAI in Nigeria. The study was carried out in a cross section of 24 commercial poultry farms in four States in South West and North Central Nigeria. Five hundred and one sera collected randomly were screened by agar gel immunodiffusion (AGID) assay for antibody to group specific influenza A nucleoprotein. One hundred and eight sera obtained from five H5N1 infected poultry farms were also concurrently screened. Reactive sera were further analysed by Hemagglutinin Inhibition (HI) test against H5 antigen using 1% suspension of pooled washed chicken red blood cells. Only 8 out of 501 sera (1.6%) had evidence of influenza A antibody. All of the 8 samples were from one farm with 20 samples collected representing 40% seroconversion at farm level. Three out of those sera were positive for H5 at HI titer of 3log2. All other sera including those obtained from HPAI infected farms were negative for influenza antibody. This study confirms limited antibody response to avian influenza  subtype H5 most likely due to vaccination in one commercial flock. Vaccination against avian influenza by farmers desperate to protect their investments may lead to unregulated and suboptimal application of vaccines requiring farmers’ and stakeholders’ engagement to forestall negative impact.

Keywords: Avian influenza; Control measures; Recurrent outbreaks; Vaccination status.