Avian Influenza-Killed Vaccine on Tissue Distribution and Shedding of Avian Influenza Virus H9N2 in Ducklings

Ducks play an important role in the transmission of avian influenza to poultry farms. Because of the importance of vaccination in reducing virus shedding, this study evaluated avian influenza-killed vaccine H9N2 on tissue distribution and shedding of avian influenza virus H9N2 in ducklings. One hundred-day-old ducklings were purchased and, after bleeding from 20 birds, were kept in four separate rooms under standard conditions. Groups 1 and 2 were vaccinated at 9 days, and groups 2 and 3 were challenged with 0.1 ml of allantoic fluid containing 105 EID50 (A/chicken/Iran/Aid/2013(H9)) virus intranasally at 30 days. Group 4 chicks were kept as the control group. Chicks were observed two times daily. On days 1, 3, 5, and 8 after inoculation, 3 chicks were randomly selected from each group and cloaca and trachea swabs samples were collected from each bird. Then the ducklings were euthanized and trachea, lung, spleen, intestine, liver, and brain tissue samples were collected for molecular detection. The virus was detected in the tissues and tracheal and cloacal swabs by polymerase chain reaction (PCR), and anti-AIV titres were measured by HI test. The results showed no clinical signs in the challenged groups. In the vaccinated challenged group, virus was detected only in cloacal swabs, but in the unvaccinated challenged group, virus was detected more in tracheal swabs than in cloacal swabs. In challenged-unvaccinated chicks, virus was detected in the trachea and lungs, and in challenged-vaccinated birds, virus was detected in the intestines. In conclusion, vaccinating ducks against the AI H9N2 virus reduced shedding and tissue distribution of AI viruses in challenged ducks.