Pathogenicity Study of Ducks Infected with Local Isolate of Highly Pathogenic Avian Influenza-H5N1-Clade 2.3.2

The early outbreak of highly pathogenic avian influenza in poultry in Indonesia was caused by H5N1 clade 2.1.3, whereas the second outbreak in ducks was caused by 2.3.2 clade introduced from abroad. The study aims to determine the pathogenicity of local isolates of H5N1 clade 2.3.2 in ducks based on histopathological and immunohistochemical approaches, compared to clade 2.1.3 local isolates. Fifteen ducks were used and kept in the BSL-3 modular laboratory. Three ducks were served as negative control and six ducks were infected with 10 6 EID 50 viruses intranasally: two ducks were infected with 2.1.3 isolate (A/chicken/West Java/Krw54/2012), two were infected with 2.3.2 isolate (A/Environment/East Java/LBM-LM13/2012) and two were infected with 2.3.2 isolate (A/duck/Sukoharjo/BBVW1428-9/2012). Another six were infected by direct contact with infected ducks. Visceral organs were collected for histopathology and immunohistochemistry. Intranasal and contact infection the clades caused mortality 50% in 3-7 dpi, produced nonsuppurative inflammations in the brain, heart, lungs, liver, intestines, pancreas, and kidneys with various degrees of severity and antigen distribution level. Lamongan and Wates isolates belong to clade 2.3.2, they can produce different degrees of severity and amount of antigen for the same route of infection. This study shows that the origin of the isolate plays a more important role in determining pathogenicity rather than the route of infection. The study showed that Wates isolate (clade 2.3.2) was the most pathogenic, followed by Lamongan (clade 2.3.2) and Karawang isolates (2.1.3), respectively. The order of pathogenicity indicates that clade 2.3.2 is more pathogenic than clade 2.3.1.