The Epizootic Ulcerative Syndrome (EUS)-Associated Virus: Evidence Of In Vivo Pathogenicity To Snakeheads (Ophicephalus striatus)     Gilda D. Lio-Po1, Lawrence J. Albright2, Garth S. Traxler3 and Eduardo M. Leaño1   Aquaculture Department, Southeast Asian Fisheries Development Center, Tigbauan, Iloilo 5021, Philippines; 2Department of Biological Sciences, Simon Fraser University, Burnaby, B.C. V5A 1S6, Canada; 3Pacific Biological Station, Nanaimo, B. C. V9R 5K6, Canada Rhabdovirus isolated from Epizootic Ulcerative Syndrome(EUS)-affected snakeheads in the Philippines were tested for pathogenicity to healthy, naive snakehead (Ophicephalus striatus) fry, fingerlings and juveniles. Virus exposure of naive snakehead fry and fingerlings by bath at 20 - 22.5oC resulted in significant mortalities (p<0.01) with no apparent lesions.Naive snakehead juveniles when injected intramuscularly (IM) with the EUS rhabdovirus at ambient water temperature (28 - 32oC) did not develop any lesion. However, similarly treated snakehead juveniles at 20 - 22.5oC developed dermal lesions 3-5 days following treatment. The lesions progressed from slight (+) to moderate (+++) lesions by days 10-12 but not to deep ulcers as exhibited by naturally EUS-affected snakeheads. Mean mortalities were higher in the virus-injected fish (72%) compared to those in controls (33%). Moreover, the virus was re-isolated from fish in the 20 - 22.5oC treatment but not from fish in the 28 - 32oC treatment. Virus from unpropagated tissue filtrate and the virus passaged 3 or 4 times induced similar dermal lesions if the EUS rhabdovirus concentration was at least 103 TCID50/fish. Regardless of organ source (liver kidney, spleen, gonad, gills, dermal lesion), the EUS rhabdovirus caused dermal lesion development at day 5. When administered orally, by bath, by intraperitoneal (IP), IM and subdermal (SD) injections to snakehead juveniles, only the latter two viral routes induced dermal lesions. However, IP injection of the EUS rhabdovirus caused 75% mortalities but none in control fish. The results demonstrate the pathogenicity of the EUS rhabdovirus to naïve snakeheads at low (20 - 22.5oC) rearing water temperatures.