Comparison of different inoculation methods of H9N2 subtype avian influenza virus in broiler chickens

H9N2 of avian influenza (AI) subtype has been reported from commercial poultry farms in many countries. This virus has been circulating in poultry industry of different parts of Iran for the last decade. To study the infection of avian influenza H9N2 in chicken of Kerman, one of the characterized H9N2 subtype of Iranian isolate was inoculated by intravenous (IV), intratrachea (IT), and intranasal-ocular (INO) routs in 6-week-old broiler chickens. The trachea, lung, kidney, and fabriciuos bursa tissues were taken at 1–10?days post-inoculation (PI). Each of the samples was divided into two parts. One part was kept in ?70°C for virus isolation. The second part was kept in formalin buffer for preparing paraffin embedded tissue sections. The tissue sections were subjected to indirect immunofluorescence assay (IIF) assay using a monoclonal antibody against N2 influenza antigen and goat-anti-mouse fluorescein isothiocyanate (FITC) conjugated antibody. The results showed that the inoculated virus isolated from lung and kidney by IV, trachea and lung by IT, and trachea by INO methods. The sensitivity and specificity were 88% and 60% for IIF assay, respectively. In addition, the positive and negative prediction values were 64% and 86%, respectively. The accuracy IIF assay compared with virus isolation was 73.3%. It could be suggested that specificity and positive and negative prediction values for tissue samples testing were better in IIF assay using monoclonal antibodies than the virus isolation test.