Received: 25-07-2017 / Accepted: 15-01-2018
To evaluate the pathological changes of chickens vaccinated against avian influenza (AI), then challenged with a virulent AI virus, experiments were conducted using a virulent A/H5N1 virus belonging to clade 2.3.2.1C (A/Ck/Vietnam(KienGiang)/NCVD15A7/2015(H5N1)). After virulent challenge, the dead chickens or chickens surviving until the end of the experiment were examined for macroscopic and microscopic lesions of the visceral organs. The examined specimens were visceral organs and macroscopic and microscopic lesions were examined by thorough necrosy and microscopical examination of HE stained specimens. The chickens were divided into 4 groups: Three experimental groups were vaccinated against AI and unvaccinated chickens as control. Chickens in all 4 groups were intranasally challenged with a virulent virus of 106TCID50/100 ul/animal and monitored for 10 days after challenge. The results showed that all control chickens died before the experiment ended, while 21/30 chickens of 3 experimental groups survived. Macroscopic lesions in chickens of chicken group vaccinated with Navet-vifluvac vaccine were pulmonary edema, congestion and hemorrhage. For chickens of chicken group vaccinated with Re-5 vaccine, in addition to pulmonary edema with swelling, congestion and hemorrhage, there were also hemorrhage in the thigh muscle, neck, intestines and liver. For chickens of chicken group vaccinated with Re-6 vaccine, pulmonary odema and spot haemorrhage were observed. Chickens of control group showed lesions typical for chickens infected with AI viruses. Microscopic lesions in the control chicken were severe and typical of AI. This indicated that unvaccinated chickens, after challenged with a virulent A/H5N1 virus exhibited more severe and typical lesions than vaccinated chickens, then challenged with the virulent virus.