User blog comment:Kogath/Monster Hunter 4 Ultimate for the Nintendo 3DS/@comment-21371438-20140128193758/@comment-184612-20140129165008

From what I've gathered from playing, while the virus is harmful to humans (the debuff is rather annoying), it's only temporary due to the human body being able to fight off the infection. With monsters the infection is permanent, but it enhances their abilities instead.