Pathogenicity of avian influenza virus H5N1 2007 isolates from Pakistan

To assess the pathogenicity and to categorize the high pathogenic avian influenze (HPAI) H5N1 of four isolates from different outbreaks during 2007. Primary assays of pathogenicity test were used such as mean death time (MDT), intracerebral pathogenicity index (ICPI) and intravenous pathogenicity index. The MDT of isolate 1, 2, 3 and 4 was 35 h, 36 h, 38 h and 35 h respectively in ten-day old chicken embryonated eggs. The ICPI in one day old chick for all isolates were more than 0.7 and the intravenous pathogenicity indexes in six-week old specific pathogen free chicken for all isolates were more than 0.7 and 1.2. It is the first report of pathogenicity assessment of H5N1 virus circulating in Pakistan and all isolates were categorized to HPAI viruses through primary methods of pathogenicity test.