Clinical findings in poultry infected with highly pathogenic avian influenza - field observations

Abstract

Highly pathogenic avian influenza (HPAI) is an extremely contagious, infectious, systemic disease of poultry, which leads to high mortality and nervous, hemorrhagic and inflammatory changes in several internal organs, brain and skin. As natural hosts for avian influenza virus (AIV), wild birds, particularly aquatic birds, are the primary reservoir for transmission of AIV to domestic poultry. The incubation of the disease varies greatly, from a few hours to 14 days, while the symptoms can be extremely different. In the last 6 years, two epizootics of highly pathogenic avian influenza have occurred in the area of South Bačka District (Republic of Serbia), The first epizootic was in the period between November 2016 and April 2017, with highly pathogenic avian influenza H5N8, while the second epizootic was between November 2021 and January 2022, caused by H5N1. Mute swans were the most affected species, along with poultry and ducks. In most cases sudden death occurred in mute swans with asymptomatic clinical form of avian influenza. Poultry and other wild birds usually died from HPAI with few clinical symptoms, poor activity, dehydration, reduced food intake resulting in severe depression and death. However, torticollis, paresis, paralysis, excitations, convulsions, rollovers or circular movements occurred in some birds that survived the peracute phase when the disease progressed to the acute phase. The aim of this study is to point out the clinical symptoms that can be observed in infection with highly pathogenic avian influenza and to highlight the importance of recognizing the symptoms in order to detect this disease.