My understanding was that Carter was a marine biologist, not a virologist. Has anything he has “written … about this” been of sufficient rigor as to make it into mainstream virology journals? In what lab has he done primary research on cross-species infections?
“Has written about”, and even " has written a whole lot about" offers no real indication that the author actually knows what they’re writing about.
Addendum:
Why exactly should we be taking Carter’s word for it?