Avian Influenza H5N1 Isolated from Bali, its Safety and Potential as a New Vaccine Candidate

ABSTRACT Avian Influenza H5N1(AI-H5N1) is a highly contagious viral disease that causes high morbidity and mortality in chickens. As in many infected countries, the disease has been endemic in Indonesia since 2005, and vaccination to control it had massively been implemented but the outbreak has been frequently reported. One of the most critical of this condition was associated with the ability of the virus to mutate quickly leading to no protective antibodies, so it was crucial to find new locally viral candidates for a homolog vaccine. Fortunately, an AI-H5N1 isolate was successfully isolated in Bali the so-called A/Chicken/Bali9C/GAY/2019 and had been made for a new inactivated vaccine candidate and proven to be safely tested in a BSL-3 laboratory. However, this novel vaccine candidate has never been tested in the field, therefore, the aims of this research were to test the safety aspects of the vaccine in field. A total of 40 layers of Novogen Brow strain at 5 weeks old were used in this study and immunized once using the vaccine at the age of 5 weeks. Blood samples were collected one week before vaccination and repeated at one-week intervals for 5 weeks. The antibody response was tested using the HI test and hematological changes were examined using standard procedures. The results showed that antibody titers increased significantly from 1st to 4th weeks postvaccination with a titer of ?16 HI units, and after a further booster at week 4th, it reached a peak titer of about 256 HI units. Hematological data were analyzed using one-way analysis of variance (ANOVA) followed by Duncan's test using SPSS for windows. No significant difference (P>0.05) was observed in the hematological profile tested including total erythrocytes, hemoglobin, hematocrit, as well as the heterophils and lymphocytes ratio. The serological and hematological analyses suggested that this vaccine trial was valuable and safe coinciding with the clinical data that all the immunized chickens showed no clinical disease during the experimental studies. It was concluded that the A/Chicken/Bali9C/GAY/2019 had the potential to be used as novel and safe vaccine candidate, although other efficacy factors such as challenge studies and cellular immunity should be further evaluated. Key words: Layer Chickens, Vaccination, AI-H5N1, Hematological Test, H/L Ratio