6 Elements of zoning and compartmentalization
6.1 Management of a Compartment or Zone
6.1.1 Physical and Spatial Factors
Where a serious disease has been identified in a country and eradication is not feasible, establishment and maintenance of free zones can limit the impact of a disease on the ability to market products both locally and internationally (FAO, 2007b). Such zones or compartments may be established based on ecological, hydrological and climatological barriers (FAO, 2007b), bearing in mind that numerous pathogens can survive protracted periods in water and have the ability to be transmitted downstream via water and sediments.
Fomites, such as fishing equipment, fish transport tanks, people, clothes, boats and vehicles, may aid in the transfer of aquatic animal pathogens and may circumvent natural barriers between infected and noninfected zones. Within watersheds, fish migrations may be accountable for spread of certain pathogens. One example of a pathogen that has spread unexpectedly is EUS, a disease that spreads by the release of infective spores into the water. After the first outbreak of EUS, in the Zambezi River upstream of Victoria Falls in southern Africa in 2006, the disease was found to spread rapidly upstream with its greatest impact in the floodplains of the upper Zambezi, yet few cases were reported downstream of the Falls (Huchzermeyer and Van der Waal, 2012).
Where wild-to-farmed and farmed-to-wild fish interactions favour pathogen transfer, biosecurity measures, including containment and stamping out procedures, may be most successful in farms supplied by a protected water supply (Jeremic, Dobrilla and Radosavljevic´ , 2004).
The degree of confidence with which biosecurity and surveillance are applied may be influenced by a number of factors that must be taken into account, as indicated in the OIE Aquatic Animal
Health Code (OIE, 2016):
• the disease status of adjacent areas and areas epidemiologically linked to the compartment;
• the location, disease status and biosecurity of the nearest epidemiological units or other epidemiologically relevant premises;
• the distance and physical separation from other aquatic animal populations with different health status in close proximity of the compartment, including wildlife and their migratory routes;
• slaughterhouses or processing plants; and
• fish exhibitions, put and take fisheries, fish markets and restaurants selling live aquatic animals, and any other points where aquatic animals are concentrated.
Functional, structural or natural barriers must ensure that adjacent animal populations with a different health status are adequately separated from a compartment (OIE, 2016). Protected water sources are generally those that contain none of the susceptible species of a particular disease or diseases and are usually a prerequisite for the issue of specific pathogen free (SPF) certification. Spring water and borehole water are considered the safest form of water supply.
Compartments utilizing recirculated water systems based on a secure water source preclude the risk of introduction of pathogens via the water supply. Unless such a system is managed as a closed system, pathogens may still enter the system with introductions of aquatic animal stock.
6.1.2 Infrastructural Factors
Where establishing and maintaining a disease-free status throughout an entire country or zone is impossible or difficult, particularly where a specific disease exists in wild aquatic animal species or can cross international borders, recognition of disease status based on biosecurity management of a compartment is possible (OIE, 2016). With the objective to facilitate trade and minimize the impact of disease on aquaculture farms, compartments within countries or zones need to strive for third-party disease-status recognition. All epidemiological factors that affect the disease transmission are taken into account to create disease-specific separation of subpopulations (OIE, 2016). For the purpose of facilitating trade, compartments must be under the control of a relevant competent authority. A compartment should be clearly defined, taking into account physical and special factors that affect the biosecurity of the compartment (OIE, 2016). These include location of its components and related functional units such as broodstock ponds, hatchery, nursery, grow-out facilities, slaughterhouse and processing plants. The effectiveness of the compartment depends on a number of infrastructural aspects, including the following (OIE, 2016):
• water supply, in particular, the degree to which a water supply is regarded safe or protected from disease risks;
• efficacy of physical separation;
• people entry facilities (disinfectant foot baths, protective clothing, etc.) and access control;
• vehicle and vessel access, and washing and disinfection procedures;
• unloading and loading facilities;
• isolation facilities for introduced aquatic animals;
• facilities for the introduction of material and equipment;
• infrastructure for feed and veterinary product storage;
• aquatic animal waste disposal facilities;
• measures to prevent exposure to fomites, mechanical and biological vectors; and
• feed supply and source.