Survivability of Fish Pathogenic Viruses in Environmental Water,
and Inactivation and Disinfection of Fish Viruses

M. Yoshimizu, H. Takizawa, H. Kataoka, T. Yoshinaka, S. Hatori and H. Kasai

Faculty of Fisheries and Graduate School of Fisheries Sciences, Hokkaido University
Hakodate 041-8611, Japan

ABSTRACT

[Introduction] Survival of fish viruses in fish rearing water was observed. Inactivation effects of ultraviolet (UV) irradiation, ozonization, and electrolyzation of water, and virucidal effect of disinfectant against fish viruses were studied.

[Materials and Methods] Survival of three salmonid viruses; infectious hematopoietic necrosis virus (IHNV), infectious pancreatic necrosis virus (IPNV) and Oncorhynvchus masou virus (OMV), two marine fish viruses; hirame rhabdovirus (HIRRV) and fish nodavirus (BF-NNV) in fish rearing water, de-chlorinated city water, double-distilled water, and Hank's balanced water (HBSS), or coastal sea water, filtrate sea water, and autoclaved sea water, were observed at 0, 5, 10, and 15⁰C for 7 or 14 days. Interaction between viruses and microorganisms present in the rearing water was observed. Subsequently, absorption of IHNV to sea sand, Japanese acid clay, diatomaceous earth, kaolin, bentonite, quarts sand, chitin, cellulose powder, ion exchange hydrophobic Toyopearl and Cellulofine, alundum, active carbon, silica gel glass, plastic, and bacterial cells was studied. Then, inactivation effects of UV irradiation ozonization and electrolyzation of water were studied against 6 fish rhabdoviruses; IHNV, HIRRV, pike fry rhabdovirus (PFRV), spring viremia of carp (SVC), eel virus from America (AVA), and ell virus from Europe (EVEX), 3 fish herpesvirus; OMV, H. salmonis, and channel cat fish herpesvirus (CCV), fish birnaviruses; IPNV, fish reovirus; CSV, fish iridovirus; Japanese flounder lymphocystis disease virus (JF-LCDV), and fish nodavirus (BF-NNV). Virucidal effects of six kinds of disinfectants were examined against OMV, IPNV, IHNV, and HIRRV at 15 and 20⁰C for 30 sec and 20 min. Virucidal effects were measured by plaque reduction methods.

[Results and Discussion] IPNV and BF-NNV were stable in all kinds of waters used at every temperature tested for 14 days, but it was observed that, for IHNV and HIRRV, as the temperature increased, the loss of infectivity also increased. OMV was labile even in HBSS and inactivated rapidly as the temperature was raised. It was not survive at 5 to 7 days later in the fish rearing water. When IHNV and OMV were suspended in filtrated and autoclaved rearing water, infectivity was reduced in comparison with the untreated water. Representative isolates Pseudomonas flourescence strain 46NW04 has been proven to have the ability to produce anti IHNV substance (Fish Pathol., 21, 223-231; J. Aquat. Anim. Health, 2, 12-20). IHNV absorbed to several clays (Kaolin, bentonite, Japanese acid clay) and diatomaceous earth in sterilized water with a wide range of pH (5-11) at concentrations of 1,10, and 100 mg/mL. Except for bentonite, infectivity of clay-absorbed IHNV persisted for as long as 9 weeks. The clay-absorbed IHNV also persisted in infectivity to rainbow trout Oncorhynchus mykiss, causing cumulative mortality rates of more than 73%. The results suggest that IHNV absorbed to naturally occurring substances in various aquatic environments may provide a source of infection for susceptible fish inhabiting these environments (J. Aquat. Anim. Health, 12, 64-68). Six rhabdoviruses, three herpesvirus, and JF-LCDV were found to be sensitive to UV irradiation (99% infectivity reduction dose (ID99) = 103,, W.sec/cm2), ozonization (ID99.9 = total residual oxidants (TROs) 0.5 mg/L for 15 sec), and electrolyzation (ID99.9 = Hypochlorite 0.3 mg/L for 1 min). Susceptibility of IPNV, CSV, and BFNNV to UV were found to be low, and ID99 was measured 105,, W sec/cm2, IPNV, CSV were low sensitive to ozonization and electrolyzation, and ID99.9 was measured 0.5 mg/L TROs for 30 sec and 0.5 mg/L Hypochlorite for 1 min, respectively (Fish. Sci., 68 (suppl. I), 821-824). At 15⁰C for 20 min, minimum concentrations showing 100% plaque reduction of viruses tested by iodophore, sodium hypochlorite solution, benzalconium chloride solution, saponated cresole solution, formaldehyle solution, and potassium permanganate solution were 40, 50, 100, 3500, and 16 ppm, respectively (Fish Pathol., 35, 185-187).