While the quarantine system is only as strong as its physical components and the management and husbandry protocols in use. It is an accepted means to prevent introduction of infectious disease into a fish holding facility. Quarantine, coupled to purchasing from reliable sources, provides a strong level of security from introduction of infectious disease. But despite the best precautions, it is possible for disease to emerge in a facility. Breaks in biosecurity do occur. Quarantine failures, contaminated materials, failure to adhere to biosecurity, and simple accidents may result in delivery of pathogens or infected fish into a pristine tank. Managers must be prepared to deal with this situation, working to contain and eliminate the disease from the operation, and conducting a trace back investigation to determine the cause of the biosecurity break.
The methods of containment and elimination of pathogens in a facility are entwined with concepts and procedures that promote fish health and well-being. It is important to promote procedures that will assure the highest level of health in the fish, offering them the best chance to resist infection and disease by pathogens that have entered or persisted in the holding system.
Development of proper pathogen containment protocols requires and understanding of the key modes of pathogen persistence and transmission within an ornamental fish facility.
Pathogen persistence within the facility
Pathogen containment must address the persistence of pathogens within the facility. There are places in a fish holding system in which introduced pathogens may survive and perhaps even multiply. If not recognized and addressed, these persistent organisms will continue to deliver infectious agents throughout a tank or facility.
Consideration of pathogen persistence should include:
- Fish can be asymptomatic carriers of disease. THey carry a disease, show no signs of that disease but may infect other fish in the system.
- Dead and diseased fish, invertebrates, and plants may serve as pathogen reservoirs.
- The water and the life support system can also harbor pathogens. When water quality is poor, some pathogens can multiply in the water column and, if the systems are interconnected, can spread throughout multiple tanks or ponds.
- Pathogens can accumulate in the areas where water and dirt accumulate and are not easy to clean, disinfect and dry. These would include uncoated or cracked concrete, wooden tank supports, covers and tabletops, gravel pathways and low spots in the floor that are poorly drained. The use of non-porous surfaces, or waterproof epoxy coatings on porous surfaces, may help to eliminate such risks.
- Pathogens can also accumulate on equipment that is not properly cleaned and disinfected between uses.
Routes of pathogen transmission
Once established in a tank, pathogens can be moved to other tanks, systems, or facilities in several ways. These may mirror the mechanisms that allowed entry of the organism into the facility. This movement can be even more pronounced during a disease outbreak. It is important to consider these routes of pathogen dispersal and some approaches to mitigate these risks.
- Waterborne transmission: Pathogens can persist in water, some for extended periods. This is a concern with respect to incoming water as well as in-place system water. System water can be contaminated through use of untreated or unprotected water sources. This contaminated water then serves as a reservoir for pathogens within the facility. Proper treatment of the water, through mechanical filtration, chlorination/dechlorination, ultraviolet light, or ozone treatment can destroy potential pathogens carried in the water column.
- Airborne transmission: Airborne transmission of fish pathogens has significant potential for the spread of fish diseases, especially in facilities where holding tanks or ponds are in close proximity without benefit of solid covers or substantial dividers. Water splashing, whether from cascading water, moving equipment, or surface agitation from pumps or aeration, produces water droplets that can be contaminated with pathogens, forming mists that settle over adjacent surfaces, contaminating adjacent tanks or ponds. Drafts or ventilation airflow from open windows, doors, or fans can exacerbate the problem, pushing these water droplets even further. The risks of airborne transmission can be greatly reduced through the use of solid tank covers and/or splash guards between tanks. In addition, careful attention to splash reduction from pumps or cascades, or when installing or moving equipment or fish will further reduce the risk of aerosol transmission.
- Vector transmission: Vectors are living organisms that may harbor and transmit pathogens from one fish to another. Examples in the aquatic environment include the crustacean parasite Argulus sp. and some species of leeches. Pathogens harbored by these vectors can be deposited on or within fish, and disease may follow. Vectors often cause disease in their own right. Prevention of vector transmission is best achieved through control of the vectors themselves, either during quarantine or via prompt identification and control in the display or holding system.
- Fomite Transmission: Fomites are inanimate objects on which pathogens can be transmitted from location to location. This can include equipment used in a facility as well as staff and visitors. Pathogen transmission via fomites usually occurs by sharing equipment between tanks or systems without proper cleaning and disinfection after each use. To prevent this, they must be properly handled and disinfected. Each tank, isolated system, quarantine facility, and site should have its own set of equipment and instruments, including nets, totes, buckets, brushes, scrapers, siphons, and pumps. In addition, each area should have its own cleaning, disinfection, and drying station.
- Pathogen transmission in the feed: Fish foods, whether live, fresh, or frozen, carry the potential for disease transmission if contaminated by pathogens or toxins. All foods must be of the highest quality and obtained from reputable sources that understand the importance of proper feed manufacturing and storage. Just as with newly arrived fish, live foods should be quarantined, examined and treated for any identified diseases before they are used. Fresh and frozen food should be of high quality and not show any signs of spoilage or decay. Commercial feeds should be purchased in lots that can typically be fed out in 6 months, broken up into small packages for weekly or daily use, and properly stored. Feeds should not be fed if they are damp, moldy, or have a foul odor.
Your comments are always welcome. I’d be particularly interested in comments/experiences about various approaches to pathogen containment large import and/or production facilities. In the next post I’ll share some of our thoughts about implementing biosecurity into a fish health management program. TMM