6.3 Surveillance

Management of aquatic animal diseases on a farm, national, regional and international level requires relevant knowledge about the occurrence of disease.

Surveillance activities provide the information on the occurrence of important aquatic animal diseases within compartments, zones and countries. It is important to prioritize the diseases to be included in a surveillance system. This may depend on the need to provide disease-status assurances for trade purposes, the financial and socioeconomic impact of the threat that a disease poses, the importance of an industry-wide disease-control programme within a country or region, and the resources of a country (OIE, 2016).
Surveillance is the systematic ongoing collection, collation and analysis of information related to animal health and the timely dissemination of information to those who need to know so that action can be taken (Cameron, 2002; Corsin et al., 2009). For purposes of disease surveillance, farmed and wild populations and subpopulations of aquatic animals are managed as epidemiological units. An epidemiological unit represents a defined population or subpopulation of aquatic animals that share the same chance of exposure to a pathogen within a defined location in which infectious diseases can be transmitted, but that is separated from other populations by some means (Corsin et al., 2009; OIE, 2016). An epidemiological unit may represent a population of wild aquatic animals inhabiting a distinct geographic location or be as small as a single pond or cage on an aquaculture farm. Where management practices cannot preclude a common exposure route in a shared environment, the epidemiological unit becomes larger and will apply to all the ponds or cages on a farm or even to an entire waterway or catchment.

Surveillance programmes can be implemented once epidemiological units have been defined. As a minimum, this is based on comprehensive general surveillance activities aimed at establishing the extent of endemic disease situations and as an early warning system for outbreaks of new or exotic diseases (Subasinghe, McGladdery and Hill, 2004). More detailed information about the status of a defined disease is gathered through targeted surveillance aimed at a specific disease or infection (OIE, 2016).
Countries have a number of responsibilities to ensure effective disease surveillance (Subasinghe, McGladdery and Hill, 2004). These include:
• support national surveillance schemes by ensuring that relevant diagnostic capacity is available, and that field and laboratory personnel are sufficiently trained in disease recognition, reporting and accurate rapid pathogen identification;
• develop standardized field and laboratory surveillance methodologies, and training and reference manuals;
• ensure that surveillance data are entered into a national database from which the data can be rapidly accessed; and
• ensure that adequate finances are available to support active surveillance schemes.
Surveillance is usually performed to achieve one or more clear objectives, including the ability to demonstrate absence of infection needed to facilitate domestic and international movement of aquatic animals and their products, provide an early warning of the incursion of a new or exotic disease, describe occurrence and distribution of diseases relevant to official disease control measures, and assess progress in control or eradication of selected diseases (Corsin et al., 2009; Subasinghe, McGladdery and Hill, 2004).
Surveillance provides information on disease control programmes that is valuable to trading partners for import risk assessment and for the justification of import health certification requirements and to substantiate absence of disease claims required for export certification (Subasinghe, McGladdery and Hill, 2004; FAO, 2007b).
Implementing biosecurity practices and the systematic approach to gathering information on occurrence and distribution of diseases provides aquaculture farmers with the most effective means of disease prevention (Subasinghe, 2005). Aquatic animal health services require meaningful reports on disease status of zones and compartments that depend on well-designed surveillance programmes to support risk analysis and to support the rapid implementation of contingency programmes for eradication or containment of serious introduced diseases (Subasinghe, McGladdery and Hill, 2004; FAO, 2007b).
Where infrastructural development or diagnostic capacity is insufficient for national-level surveillance programmes supporting the creation of zones, surveillance of the health status of a compartment may provide sufficient information for export purposes.
Once surveillance data on the prevalence of diseases within a zone or compartment become available, steps can be taken to either:
• limit the impact of an infectious disease if present;
• eradicate the disease if present; or
• ensure that an infectious disease is not introduced if found to be absent.
Aquatic Animal Disease Surveillance and the Trade in
Live Aquatic Animals and Their Products
Domestic and international trade in live aquatic animals and products may be dependent on the ability of a producer to provide guarantees of freedom from diseases. For transboundary movement of live aquatic animals and their products, it is the importing country that states the guarantees required, usually as a condition of an import permit. Importing countries require such guarantees in order to appropriately protect the health status of aquatic animal populations within the importing country. For farmers to access transboundary markets, they need to be in a position to meet the importing country’s demands. For this purpose, surveillance of zones and compartments, at the very least at the farm level, is a prerequisite. Such demands may appear restrictive to farmers, but by adopting and adhering to the management practices required to meet strict biosecurity demands, the reduction in risk of disease outbreaks and associated cost bears substantial advantages to animal production systems.