However, the journals also reported new details about the risks of placing pig organs into humans. The editor of Nature made a compelling case for a moratorium on clinical trials of xenotransplants because of the risks, which are myriad. Although humans and other animals share many bacteria and viruses, the impact of these microorganisms is not necessarily the same in different species. A viral example, herpes B, won't kill monkeys but it will kill humans. Aids kills humans, but not chimpanzees.
Viruses are small and adaptable.
While some viruses have little or no effect, others deplete systems and bring on disease. They can lie dormant for years, like HIV, then suddenly become deadly. All viruses mutate, many times a year. They figure out how best to thrive, adapt and move on. Again, just as visible species adapt to Earth by natural selection and evolution, so too do the microorganisms living in our bodies.