Serosurvey and Isolation of Infectious Bronchitis Virus in Chickens Reared in Commercial and Semi-Scavenging Systems

Abstract

A cross sectional survey was undertaken to estimate the seroprevalence of infectious bronchitis virus (IBV) in chickens reared under both intensive and semi-scavenging systems in Bangladesh. Attempts were also made to isolate the virus from these two chicken populations. Chickens being reared under intensive system at a Government poultry farm (Pahartali Zonal Poultry Farm, PZPF, Chittagong, Bangladesh) and the semiscavenging system at Smallholder Livestock Development Project-2 (SLDP-2) areas, which is being operated in 5 southern districts of Bangladesh, were serologically investigated. The survey was conducted during the period from October 2005 to March 2006. Serum samples were at random from 184 chickens: 104 (Fayoumi and Rhode Island Red [RIR] breeds) from PZPF and 80 (Fayoumi, Sonali and indigenous) from the SLDP-2 areas. To isolate the IBV, organ samples were also collected from 100 dead chickens, 74 from PZPF and 26 from the SLDP-2 areas. Seroprevalence of the IBV in chickens was determined using Ab-ELISA test. Virological inocula prepared from the pooled organ samples of dead birds according to the standard procedure were inoculated through allantoic sac route (@ 0.2 ml inoculum/embryo) of 10-11 days' old developing-chicken embryos. The growth of the IBV was determined by finding characteristic changes in the embryos - curling and dwarfing at the age of 18 days. Allantoic fluids were harvested in positive cases. The survey revealed that, 19% (confidence intervals [CI] 11, 27%) Fayoumi and 54% (CI 35, 73%) RIR chickens reared at PZPF were seropositive to the IBV. In semi-scavenging chickens, the seroprevalence was 98% (CI 96, 100%), which is significantly higher (p = 0.00) than the chickens reared in the intensive system. Presence of the IBV was diagnosed in 11 and 6 dead chickens collected from PZPF and SLDP-2 areas, respectively.