A number of birnaviruses, rhabdoviruses and a reovirus have been isolated from occasional fish affected with the epizootic ulcerative syndrome (EUS) in the past decade. The heterogeneous nature of these isolates, together with a low and inconsistent level of recovery from diseased specimens, suggests that these viruses may only represent adventitious infections unrelated to outbreaks of EUS. Furthermore, experimental induction of the condition by direct exposure to cell culture isolated viruses has not been achieved. The significance, if any, of C-type retroviruses identified in cell cultures derived from EUS-susceptible fish species is not known.
Frerichs, G.N. Viruses associated with the Epizootic Ulcerative Syndrome (EUS) of fish in South-East Asia. Veterinary Research (1995) 26 (5-6) 449-454.