Characterization of a virus obtained from snakeheads Ophicephalus striatus with epizootic ulcerative syndrome (EUS) in the Philippines

Abstract

This is the first report of the isolation and characterization of a fish virus from the Philippines. The virus was isolated using snakehead spleen cells (SHS) from severely lesioned epizootic ulcerative syndrome (EUS)-affected snakehead Ophicephalus striatus from Laguna de Bay, in January 1991. The virus induced cytopathic effects (CPE) in SHS cells yielding a titer of 3.02 × 10 6 TCID 50 ml -1 at 25°C within 2 to 3 d. Other susceptible cell lines included bluegill fry (BF-2), catfish spleen (CFS) and channel catfish ovary (CCO) cells. Replication in chinook salmon embryo cells (CHSE-214) was minimal while Epithelioma papulosum cyprini cells (EPC) and rainbow trout gonad cells (RTG-2) were refractory. Temperatures of 15 to 25°C were optimum for virus replication but the virus did not replicate at 37°C. The virus can be stored at -10 and 8°C for 30 and 10 d, respectively, without significant loss of infectivity. Viral replication was logarithmic with a 2 h lag phase; viral assembly in the host cells occurred in 4 h and release of virus occurred 8 h after viral infection. A 1-log difference in TCID 50 titer between the cell-free virus and the total virus was noted. Freezing and thawing the virus caused a half-log drop in titer. Viral exposure to chloroform or heating to 56°C for 30 min inactivated the virus. Exposure to pH 3 medium for 30 min resulted in a more than 100-fold loss of viral infectivity. The 5-iododeoxyuridine (IUdR) did not affect virus replication, indicating a RNA genome. Neutralization tests using the Philippine virus, the ulcerative disease rhabdovirus (UDRV) and the infectious hematopoietic necrosis virus (IHNV) polyvalent antisera showed slight cross-reaction between the Philippine virus antiserum and UDRV but established no serological relationship with SHRV and IHN virus. Transmission electron microscopy (TEM) of SHS cells infected with the virus showed virus particles with typical bullet morphology and an estimated size of 65 × 175 nm. The Philippine virus was therefore a rhabdovirus, but the present study did not establish its role in the epizootiology of EUS. KEY WORDS: Epizootic ulcerative syndrome (EUS) · Fish rhabdovirus · Characterization · Ophicephalus striatus · Snakehead · Disease · Cell susceptibilityResale or republication not permitted without written consent of the publisher Dis Aquat Org 43: 191-198, 2000 tius spp., serpent fish Channa spp. and spiny eels Fluta alba (Tonguthai 1985). Outbreaks are more common between the months of September and March, which correlates with the time when lowest water temperatures occur.Several species of bacteria and fungi have been found to be associated with EUS-affected snakeheads Ophicephalus striatus, but these have not been conclusively shown to be the primary disease agents of EUS (Lio-Po et al. 1992, 1996, 1998, Roberts et al. 1993, Callinan et al. 1995. Lilley & Roberts (1997) reported the histological invasiveness of the EUS-associated Aphanomyces through the fish muscles after experimental exposure, but the development o...

Horizontal transmission of epizootic ulcerative syndrome (EUS)-associated virus in the snakehead Ophicephalus striatus under simulated natural conditions

“…In previous studies on EUS, viral isolations used pooled tissues (Frerichs et al 1986, Lio-Po et al 2000. However, in the present study, the virus was recovered from all test organs, indicating that the EUS virus is not organ-specific.…”

“…The virus was found to be serologically related to the EUS rhabdovirus by neutralization tests using polyclonal antisera raised against the EUS rhabdovirus isolate, as described in a previous study (Lio-Po et al 2000). The overall success rate in viral isolations among experimental snakeheads in this study was 21%, although Fig.…”

“…Together with the isolation of the virus from the ovaries of EUS-affected fish, this suggests that vertical transmission of the EUS virus may be possible. It may also partially explain the persistence of EUS virus in fish populations in enzootic sites resulting in annual outbreaks of EUS.In previous studies on EUS, viral isolations used pooled tissues (Frerichs et al 1986, Lio-Po et al 2000. However, in the present study, the virus was recovered from all test organs, indicating that the EUS virus is not organ-specific.…”

“…have been associated with EUS-affected fishes (Llobrera & Gacutan 1987, Boonyaratpalin 1989, Costa & Wejeyaratne 1989, Torres 1990, Lio-Po et al 1992, Roberts et al 1993, Pathiratne et al 1994, Angka et al 1995, Callinan et al 1995, Karunasagar et al 1995, Willoughby et al 1995, Lilley & Roberts 1997, Igbal et al 1999, Rahman et al 1999). In addition, previous studies have demonstrated the presence of rhabdovirus among fishes affected with EUS in the Philippines (Lio-Po et al 2000). In Thailand, Myanmar and Sri Lanka, the ulcerative disease rhabdovirus (UDRV) and the snakehead rhabdovirus (SHRV) were likewise isolated from EUS-affected snakeheads (Frerichs et al 1986, Ahne et al 1988, Kasornchandra et al 1992, Lilley & Frerichs 1994, Kanchanakhan et al 1999.…”

Scanning electron microscopic studies on surface microstructural features of some tissues of epizootic ulcerative syndrome‐affected Puntius ticto (Hamilton, 1822) from Southern Assam of India

“…The claims of different authors on association of various pathogenic microbes, e.g., bacteria (Chakraborty and Dastidar, 1991;Chakraborty et al, 1996;Mastan and Qureshi, 2001;Mukherjee et al, 1995;Rahman et al, 2002), virus (Frerichs, 1995;John et al, 2001;Lio-po et al, 2000), fungus (Lilley, 1999), etc., could not be established completely through histopathological, microbiological, and electron microscopical studies. A number of birnavirus, rhabdovirus, and reovirus have been isolated occasionally from fish affected by EUS in Southeast Asia, but it was suggested that the virus only represent adventitious infections unrelated to outbreak of EUS (Frerichs, 1992(Frerichs, , 1995.…”