Comparative thermostability analysis of zoonotic and human influenza virus A and B neuraminidase

Neuraminidase (NA) thermostability of influenza A and B viruses isolated from birds, swine and humans was measured to evaluate its variability associated with host body temperature. The highest 50% inactivation temperature (IT(50)) was observed with H3N8 avian influenza virus (74 °C), and the lowest IT(50) was observed with the seasonal human H3N2 virus (45.5 °C). The IT(50) values of A(H1N1)pdm09 viruses 56.4-58.5 °C were statistically higher than that of the prepandemic strain A/Solomon Islands/03/06 (52.5 °C). An analysis of Ca(2+) binding sites revealed the correspondence of amino acid changes to NA thermostability. This study demonstrates that changes in NA thermostability correspond to differences in host body temperature.