Outbreaks of acute infectious bursal disease of chickens in Maiduguri, Nigeria (2008-2018): retrospective survey

Abstract

Abstract Acute infectious bursal disease (IBD) outbreak caused by virulent IBD virus undermines profitable chicken production in Nigeria. Veterinary clinic-based passive surveillance is carried out by postmortem diagnosis of clinical cases submitted during disease outbreaks. Records of IBD outbreaks from two veterinary hospitals in Maiduguri, Nigeria, were extracted among all disease outbreaks in chicken flocks in the period 2008-2018. Data showed that IBD outbreaks occurred in 493 (7.6%, [95% CI: 7.0-8.3%]) out of 6,486 disease outbreaks in chicken flocks within the period. The year-specific prevalence of outbreaks varied from 1.6% (95% CI: 0.9-2.3%) to 17.3% (95% CI: 12.9-21.7%) and fitted a linear trend (r = -0.73; P<0.01) over the years, with significant (P<0.001) association with the years. The chicken-type-specific prevalence varied significantly (P < 0.05) with 25.0% in Noilers (dual-purpose), 7.2% in broilers, 7.1% in layers, 9.1% in local chickens (9.1%) and 17.4% in exotic cockerels. The ages of chickens at the time of outbreaks were 2-27 weeks; modal age was 4-5 weeks while mean age was 5.0±1.7 weeks. The mortality rate was 12.6% (95% CI: 5.9-16.2) out of total flock size of 38,485 in 2015-2018. Specific lesions for diagnosis of acute IBD during surveillance were acute exudative inflammatory swelling of bursa of Fabricius [+/-hemorrhages] (90.9%), along with hemorrhages in thigh, leg and/or breast muscles (72.2%), mucosal hemorrhages at proventriculus-ventriculus junction [+/- enteritis] (24.9%), and nephropathy (7.7%); but few cases lacked bursal swelling (9.1%). Thus, acute IBD outbreak in chickens was endemic with time-related risk factors unaccounted for during passive surveillance.