H9N2 avian influenza virus-induced conjunctivitis model for vaccine efficacy testing

Clinical signs such as respiratory signs, egg drop, and mortality have been reported in field cases of low pathogenic avian influenza by H9N2 avian influenza virus (AIV) but have rarely been reproduced by the virus alone. Thus, virus reisolation rates and titers in tissues were measured for vaccine efficacy testing. In the present study, we established a clinical sign-based vaccine efficacy test by reproduction of highly frequent conjunctivitis (77.8%-90%) via binocular instillation of an H9N2 virus (01310) strain, 1 x 10(6) EID50/10 microl for each eye). Specific-pathogen-free chickens were assigned to vaccine and control groups, and the vaccine group was inoculated intramuscularly with a commercial H9N2 inactivated oil emulsion vaccine. The chickens were challenged by 01310 via binocular instillation at 2 and 4 wk postvaccination (WPV). The positive rates of conjunctivitis and virus reisolation were significantly different between the vaccine and control groups (conjunctivitis at 2 WPV, 0% vs. 77.8%, and at 4 WPV, 0% vs. 80%). Vaccine antibody was detected in tears as well as in serum samples of the vaccine group before challenge. The conjunctivitis model may be useful for efficacy testing of AI vaccine due to a clinical symptom-based read of results, but further efficacy testings with different types, doses of AI vaccines, and challenge viruses will be required to complete the evaluation of our model.