Molecular and histopathological studies on commercial vaccines against H9 avian influenza in broilers

Abstract

Avian influenza virus is one of the major threats that has been affecting the poultry industry in the Middle East region for decades. Many trials were made to eradicate the disease, but it doesn’t work. Nowadays, there are many commercial vaccines that are either imported or prepared from circulating isolates from H9N2 in Egypt and Middle Eastern countries. This study focused on understanding the effectiveness of five commercial vaccines for their ability to give protection. Six groups of one day-old broiler chicks (n=15) were placed under normal conditions in separate pens. Each group was immunized with the specific vaccine at 4th day of age and then they were challenged with H9N2 virus at 14 days old. After challenge, respiratory signs, swelling of head, reduction in the feed consumption rate, decrease in the average body weight and general depression were observed. Postmortem findings of the euthanized birds revealed congestion of lung, tracheitis, swelling of kidneys and inflammation of bursa of fabricius. On histopathological examination, bursa of Fabricius shows different lesions of interfollicular edema, lymphocytic depletion, necrosis and sloughing of lymphoid cells which illustrates the immunosuppressive effect of the virus. The unvaccinated challenged group sheds the highest titer (mean 104.7 EID50/ml) while the remaining vaccinated groups sheds lowest titer (mean 101 - 104 EID50/ml). The vaccinated birds show less signs of disease, less degree of pathological lesions and lower viral shedding titer. This explains the importance of using H9N2 different inactivated vaccines in poultry farms for controlling the spread of the disease