 Pathogens of more distantly related species, on the other hand, such as plant viruses, are not known to infect humans .
<clarity>  Pathogens of more distantly related species, on the other hand, such as plant viruses, are not known to infect humans .
 Pathogens of more distantly related species, on the other hand, such as plant viruses, may not be capable of infecting humans at all .