A case report on outbreak investigation of newcastle disease in backyard poultry with coinfection of Escherichia coli and Bacillus spp. in Pahang, Malaysia

Newcastle Disease (ND) remains a major threat to poultry health globally, particularly in endemic regions such as Malaysia. In March 2023, a suspected ND outbreak was reported in a backyard poultry flock in Sungai Lembing, Kuantan, Pahang. This flock consisted of ten mixedbreed fowls acquired from an unverified source and there was no record of vaccination. The affected birds presented with clinical signs such as inappetence, lethargy, respiratory distress, excessive salivation, and sudden death. At the time of investigation, only one bird was still alive. Two carcasses and the remaining live birds were submitted for diagnostic testing. Post-mortem examinations revealed lesions such as congested trachea and lungs, cloudy eyes, and intestinal inflammation. Virological testing confirmed the presence of Newcastle Disease Virus (NDV), while tests for Avian Influenza (AI) and Infectious Bronchitis (IB) were negative. Bacteriological testing identified co-infections with Escherichia coli and Bacillus species in two birds, indicating possible aggravation of disease severity. The source of infection is suspected to be horizontal transmission from wild migratory birds in nearby paddy fields. The objective of this report is to investigate the cause of the outbreak, explore contributing epidemiological factors, and provide recommendations for effective prevention and control. This outbreak, resulting in 90% mortality highlights the risks posed by unvaccinated and unmanaged backyard flocks. It underscores the critical importance of surveillance, responsible poultry sourcing, public awareness, and integrated diagnostics to control ND in high-risk environments.