Evolutionary relationship of NA gene of Pakistani HP H5N1 viruses compared with other representative H5N1 viruses. The nucleotide coding regions tree was generated by neighbour joining method (with Maximum Composite Likelihood) as implemented in MEGA version 4. Numbers at the nodes indicate confidence level of a bootstrap analysis with 1000 replications as a percentage value. Scale bar indicates 0.01 nucleotide substitutions per site. The Pakistani poultry and wild/domestic bird isolates are marked in dark circles and dark squares respectively. Tree is midpoint rooted.