Protecting Fish and Fish Farmers from Infectious Disease

Transcription

1 Protecting Fish and Fish Farmers from Infectious Disease UV Disinfection Systems for Aquaculture Biosecurity The battle with fish pathogens has afflicted the aquaculture industry since its inception, but rarely has a disease caused more severe losses or been as difficult to control as infectious salmon anaemia (ISA) virus, a disease that hit aquaculture farms in Norway in At first ISAV spread slowly, passed on by the blood, mucus, and feces of diseased fish, but eventually the virus infected over 100 Norwegian fish farms and was declared a notified disease, required by law to be reported to government authorities. The global damage to fish stocks and the economy was substantial; the annual cost in 1999 was estimated at $32 million in Scotland and $14 million in Canada (Hastings, 1999). Recognizing a threat to an economically significant industry and important food source, governments around the world began to develop and enforce strict aquaculture biosecurity measures. Chief among the most effective biosecurity measures is ultraviolet (UV) irradiation, the focus of this paper. Biosecurity Requirements Norwegian Sea Norway Biosecurity measures are policies and management techniques to safeguard environmental integrity. They are crucial to reducing the risk of transmission of infectious diseases and invasive species. Biosecurity measures have been effective in the agriculture industry for decades, but have only been applied to the aquaculture industry more recently, following disease outbreaks such as ISA virus. Aquaculture biosecurity measures include disinfecting water, monitoring and reporting diseases, and rapid culling or quarantining of infected organisms in response to a disease outbreak. Norway was the first country to institute biosecurity measures in the aquaculture industry by establishing disinfection requirements at both the intake and outflow of aquaculture facilities to help prevent the spread of pathogenic bacteria, fungi, and viruses. Following very costly ISA virus outbreaks in New Brunswick, Scotland, Shetland, and Chile, other countries have adopted similar aquaculture biosecurity measures to check infections before they become epidemics that adversely affect fish stocks, decrease economic value, and dampen consumer demand through lack of confidence in the safety of farmed aquatic organisms. Norway s strict disinfection requirements apply to intake water for operations involving hatching and fish rearing, effluent water from land-based aquaculture sites and processing plants, and transport water carried by wellboats. Disinfection may be accomplished by a number of methods, including filtration, ozonation, chemical application, mechanical separation, chlorination, heat treatment, and ultraviolet (UV) irradiation. Disinfection by UV is one of the most effective and efficient of these methods. Aquaculture Page 1

2 Ultraviolet Disinfection Disinfection by means of UV is highly attractive as a cost-effective method of pathogen control. UV irradiation has been used to disinfect drinking water supplies and wastewater since the mid-20 th century and was more recently employed in the aquaculture industry with great success. UV inactivates pathogens by disrupting the pathogen s genetic material, a process called dimerization (see Figure 1). The most effective wavelength for disinfection is 254 nm and is produced by low pressure UV lamps. The mechanism of UV irradiation inactivates most bacteria, viruses, spores, and cysts without the production of chemical by-products that adversely affect fish stocks or humans, a significant advantage over other methods of disinfection. Other advantages of UV disinfection are the minimal time UV needs to be applied and the small footprint occupied by a UV system. Disinfection by UV is userfriendly, as UV systems are easy to operate and preclude the use of hazardous or corrosive chemicals. In order to effectively disinfect water flowing into or out of aquaculture facilities, it is necessary to understand the required UV dose. The UV dose required for disinfection depends on the level of disinfection desired and the particular pathogen. UV dosing studies should use methods verified according to a third-party protocol such as the UV Design Guidance Manual by the US EPA (USEPA, 2006). A summary of the most influential studies on the UV dose that inactivates 99.9% of a given pathogen in provided in Table 1. Table 1: UV sensitivity of selected fish pathogens. Pathogen Bacteria Minimum UV dose for 3 log reduction (mj/cm2) Source Aeromonas hydrophilia 5.0 Yoshimizu et al., 1990 Aeromonas punctata 4.0 Yoshimizu, 1990 Aeromonas salmonicida 5.9+, 4.0, Liltved & Landfald, 1996; Yoshimizu et al., 1990; Liltved et al Escherichia coli O Yoshimizu et al., 1990 Figure 1: The 254 nm wavelength of UV light chemically bonds DNA bases and disrupts DNA replication. Pseudomonas fluorescens 5.0 Yoshimizu et al., 1990 Vibrio anguillarum 4.5^, 4.0, Yoshimizu et al., 1990; Liltved et al., 1995 Vibrio salmonicida Liltved et al., 1995 Yersinia ruckeri Liltved et al., 1995 Protozoa Myxobolus cerebralis 40~, 40+ Hedrick et al. 2007, Hedrick et al Fungi Achlya flagellate 220# Yoshimizu et al., 1990 Aphanomyces laevis 210# Yoshimizu et al., 1990 Saprolengia anisospora 150# Yoshimizu et al., 1990 Saprolengia diclina 230# Yoshimizu et al., 1990 Saprolengia ferax 230# Yoshimizu et al., 1990 Saprolengia parasitica 230#, 200# Yoshimizu et al., 1990 Saprolengia sp. Tokyo, Shizuoka, and Cifu 250#, 230#, 220# (respectively) Yoshimizu et al., 1990 Ultraviolet light destroys microorganisms by changing their genetic information DNA. Viruses Atlantic halibut nodavirus 105 Liltved et al., 2006 Channel catfish herpesvirus 3.0-, 2.0, 1.0 Chum salmon virus 150-, 100, 100 Yoshimizu et al., 1986; Yoshimizu et al., 1990; Yoshimizu et al., 1986; Yoshimizu et al., 1990, Eel virus from America Aquaculture Page 2

3 Microscopic view of bacteria. Eel virus from Europe X Fish nodavirus 100- Herpesvirus salmonis 3.0-, 2.0-, Yoshimizu et al., 1989; Yoshimizu et al., 1990; Hiramine rhabdovirus Infectious hematopoietic necrosis virus 10, 3.0-, 3. 0, 2.0, 1.0 Yoshimizu et al., 1991; Yoshimizu et al., 1986; Yoshimizu et al., 1990; Yoshimizu et al., 1990; Infectious pancreatic necrosis virus 337, 246, 150-, 122, 119, 100- Liltved et al., 2006; Yoshimizu et al., 1990; Yoshimizu et al., 1986; Liltved et al., 1995; Oye & Rimstad, 2001; Infectious salmon anaemia virus 7.5, 7.2, 5.1, 3.3 Liltved et al., 2006; Oye & Rimstad, 2001; Oye & Rimstad, 2001; Oye & Rimstad, 2001 Japanese flounder lymphocystis disease virus 100- Koi herpesvirus 4.0Δ Kasai et al., 2005 Oncorhynchus masou virus 3.0-, 2.0-, Yoshimizu et al., 1986; Yoshimizu et al., 1990; Pike fry virus Sea bass neuropathy nodavirus 211 Frerichs et al., 2000 Spring viremia of carp virus Viral hemorrhagic septicaemia virus 7.9, 3.1 Oye & Rimstad, 2001; Oye & Rimstad, = 5 log (99.999%); + = 4 log (99.99%); - = 2 log (99%); ~ = absence of microscopic lesions, myxospores, and parasite DNA detected by qpcr; ^ = %; # = inhibited growth ; Δ = 100% plaque reduction The results in Table 1 also show that there is a wide range of UV sensitivities among different pathogens. In general, bacteria are more sensitive (easier to inactivate) than viruses and protozoa, while fungi are the least sensitive. The observed variation in UV sensitivity is primarily due to the methods used to study pathogen inactivation and the pathogen species itself. The past two decades of research into the UV sensitivity of fish pathogens has helped the aquaculture industry dramatically improve its application of UV for disinfection. UV systems can now be custom-designed to provide a UV dose that inactivates more than 99.9% of a specific pathogen. Testing a UV system for the inactivation of every fish pathogen is too costly and time-intensive to be feasible. With this in mind, Norwegian scientists and policymakers selected two pathogens to serve as model organisms when developing their nation s biosecurity measures. If there is evidence that these model organisms have been inactivated, it is likely that similar pathogens have also been inactivated to the same degree. In selecting the model organisms, both the frequency and severity of disease caused by these and similar pathogens were taken into account. The UV systems that are proven to inactivate 99.9% of the model organisms are then certified as safe for the industry. The model organisms selected by Norwegian authorities to assess the necessary dose of UV required to protect fish stocks are Aeromonas salmonicida subsp. salmonicida and the ISA virus. The minimum disinfection requirement is 3 log (99.9%) inactivation of one of these model organisms. Any UV system offered to the Norwegian aquaculture industry must prove its ability to disinfect water by meeting this disinfection requirement and passing the approval process established by the Norwegian Veterinary Institute (NVI). Xylem s Role in Aquaculture Biosecurity Xylem is committed to ensuring the security and success of the aquaculture industry through our monitoring, data management, pumping, heating/cooling, and disinfection systems. Committed to cost-effective, science-based solutions, Xylem has harnessed fish pathogen UV sensitivity data to design UV systems that Aquaculture Page 3

4 are the best in the industry. Three of Xylem s WEDECO UV systems, the BX/LBX, B-PE, and Quadron UV series, were certified by the Norwegian Veterinary Institute (NVI) in June The BX and B-PE models were approved for water intake in the aquaculture business and the Quadron model was approved for the treatment of wellboat water used in the transport of aquatic organisms. These and other WEDECO models, such as the Spektron and the open-channel UV systems Duron and TAK, have also been validated by the industry standard German Association of Gas and Water (DVGW), the ultraviolet disinfection guidance manual (UVDGM), and the US National Water Research Institute (NWRI), reflecting the high quality of Xylem s suite of UV systems. Table 2: Flow and approvals of selected WEDECO UV systems. Xylem is expanding the corrosive-resistant range of UV systems to higher flow rates. WEDECO Main Application Maximum Flow USEPA Recirculation system intake water 375 m³/h Recirculation system intake water 2,120 m³/h Wellboats applications with space constraints 4,100 m³/h Wellboats 1,335 m³/h Effluent Intake Water 250 m³/h (HDPE) NWRI DVGW NVI Approved A/B PE Series BX Series Quadron Series WEDECO UV System lamps. LBX TAK Smart Series Learn More If you would like to learn more about how Xylem can solve your aquaculture challenges, please visit: Xylem s UV disinfection systems are installed throughout the world in order to meet the demand for purified drinking water, process water, ballast water, and wastewater. Xylem s top-of-the-line systems serve the aquaculture industry with the most up-todate technology, the quality of which has been recognized by the regulators and certifiers around the world, and now the aquaculture industry standard, Norwegian Veterinary Institute. Xylem is continuing to work with customers, regulators, and research institutes to refine our ability to treat pathogens threatening the aquaculture industry. Aquaculture Page 4

5 Sources Frerichs, G.; Tweedie, A.; Starkey, W.; Richards, R Temperature, ph and electrolyte sensitivity, and heat, UV and disinfectant inactivation of sea bass (Dicentrarchus labrax) neuropathy nodavirus. Aquaculture. 185, Hastings, T.; Olivier, G.; Cusack, R.; Bricknell, I.; Nylund, A.; Binde, M.; Munro, P.; Allan, C Infectious salmon anaemia. Bulletin of the Euopean Association of Fish Pathologists. 19, Hedrick, R.; McDowell, T.; Mukkatira, K.; MacConnell, E.; Petri, B Effects of freezing, drying, ultraviolet irradiation, chlorine, and quaternary ammonium treatments on the infectivity of myxospores of Myxobuls cerebralis for Tubifex tubifex. Journal of Aquatic Animal Health. 20, Hedrick, R.; Petri, B.; McDowell, T.; Mukkatira, K.; Sealey, L Evaluation of a range of doses of ultraviolet irradiation to inactivate waterborne actinospore stages of Myxobolus cerebralis. Disease of Aquatic Organisms. 74, Kasai, H.; Muto, Y.; Yoshimizu, M Virucidal effects of ultraviolet, heat treatment and disinfectants against Koi Herpesvirus (KHV). Fish Pathology. 40, Kasai, H.; Yoshimizu, M.; Ezura, Y Disinfection of water for aquaculture. Fish Science. 68 (Supp. I), Liltved, H.; Landfald, B.; Influence of liquid holding recovery and photoreactivation on survival of ultraviolet-irradiated fish pathogenic bacteria. Water Research 30, Liltved, H.; Hektoen, H.; Efraimsen, H Inactivation of bacterial and viral fish pathogens by ozonation or UV irradiation in water of different salinity. Aquaculture Eng. 12, Liltved, H.; Vogelsang, C.; Modahl, I.; Dannevig, B High resistance of fish pathogenic viruses to UV irradiation and ozonated seawater. 34, Nylund, A.; Kvenseth, A.; Krossoy, B.; Hodneland, K Replication of the infectious salmon anaemia virus (ISAV) in rainbow trout, Oncorhynchus mykiss (Walbaum). Journal of Fish Diseases. 20, Oye, A.; Rimstad, E Inactivation of infectious salmon anaemia virus, viral haemorrhagic septicaemia virus, and infectious pancreatic necrosis virus in water using UVC irradiation. Disease of Aquatic Organisms. 48, 1-5. US Environmental Protection Agency. UV Disinfection Guidance Manual for the Long Term 2 Enhanced Surface Water Treatment Rule. EPA 815-R Washington: USEPA, Yoshimizu, M.; Takizawa, H.; Kimura, T UV Susceptibility of some fish pathogenic viruses. Fish Pathology. 21, (In Japanese with English abstract.) Yoshimizu, M. Takizawa, H. Manabu, S.; Kataoka, H.; Kugo, T.; Kimura, T. Disinfectant effects of ultraviolet irradiation in hatchery water supply. In: Hirano, R., Haoyu, I. (Eds.) The Second Asian Fisheries Forum Manila: Asian Fisheries Society. Manila, pp Yoshimizu, M.; Sami, M.; Kohara, M.; Yamazaki, T.; Kimura, T Detection of IHNV in hatchery water by molecular filtration method and effectiveness of UV irradiation on IHNV infectivity. Nippon Suisan Gakkaishi. 57, Yoshimizu, M.; Yoshinaka, T.; Hatori, S.; Kasai, H Survivability of fish pathogenic viruses in environmental water, and inactivation of fish viruses. Bulletin of Fish Research Agency. Supplement 2, Aquaculture Page 5