Particularly noteworthy was our finding of natural co-infection of a single primate host with two highly divergent SHFV variants. To our knowledge, no instance of co-infection of a single host with such highly divergent arteriviruses has previously been reported. Kibale red colobus may simply harbor a very diverse population of SHFV variants. However, it is also possible that SHFV-krc1 or SHFV-krc2 may have been transmitted to this animal from another species. For example, red colobus in Kibale form polyspecific associations with other primates, most frequently with red-tailed guenons (Cercopithecus ascanius) but also with black-andwhite colobus (Colobus guereza), blue monkeys (Cercopithecus mitis), and grey-cheeked mangabeys (Lophocebus albigena) [25] . Because such interactions can involve close proximity and direct contact, polyspecific associations could facilitate the cross-species transmission of viruses that require close contact, such as SHFV.