Annex 2 Biosecurity Zoning and Compartments, Infected Zones, Disease-Free Zones

David Huchzermeyer and Melba G. Bondad-Reantaso

1. Introduction

The impact of infectious diseases poses an everincreasing challenge to aquaculture and marketability of aquaculture products as the farming of aquatic animals increases in intensity to meet growing global demand.

Aquaculture and all levels of aquatic resource management play an important role in food security, and may have far reaching effects on rural development, water management, the environment, poverty alleviation, livelihoods, trade, and gender and household nutrition (FAO/RAP, 2003). This chapter details how the concept of biosecurity is used to limit disease transmission in the aquatic environment and how this is applied to zoning in aquaculture.
Aquaculture farming creates large densely stocked populations of aquatic animals that are susceptible to numerous infectious agents. In unstressed populations or where environmental conditions do not favour expression of clinical symptoms, a disease may go undetected. Where a contagious aquatic pathogen is present within a susceptible population of aquatic animals, the expression of disease (morbidity and mortality) will depend on numerous factors, including life stage of the host and environmental and husbandry conditions. Intense aquaculture environments tend to be conducive to expression of diseases that may remain undetected in wild aquatic animals sharing the same waters. Water in which aquatic animals are farmed provides an effective medium for the transfer of these pathogens. Where farmed and wild aquatic animals share a common water source, pathogen transfer may take place not only among the farmed population, but also from farmed-to-wild, and from wild-to-farmed individuals. Furthermore, inadvertent release of infectious agents from aquaculture farms into the naturalenvironment poses serious ecological concerns and has the potential to impact on natural species diversity.

Biosecurity zoning and compartmentalization provide a holistic approach to managing the threats posed by such diseases in the aquatic environment with the aim of establishing and maintaining populations of aquatic animals with distinct health status and effectively separating these from populations with a different health status (Zepeda, Jones and Zagmutt, 2008).
Far reaching consequences for both farmed and wild aquatic animals may occur when exotic diseases are introduced, often inadvertently, into the aquatic environment. Changes in the behaviour or distribution of an established endemic disease, or the emergence of a previously unknown disease, may be equally detrimental (Arthur et al., 2005). Disease outbreaks have proved to be one of the major constraints limiting growth and sustainability of aquaculture, and in certain

Huchzermeyer, K. D. A. & Bondad-Reantaso, M. G. 2017. Biosecurity, zoning and compartments, infected zones, disease-free zones. In J. Aguilar-Manjarrez,
D. Soto & R. Brummett. Aquaculture zoning, site selection and area management under the ecosystem approach to aquaculture. Full document, pp. 67–86.
Report ACS113536. Rome, FAO, and World Bank Group, Washington, DC. 395 pp.

instances have resulted in the complete collapse of aquaculture fisheries with serious socioeconomic impact (Bondad-Reantaso et al., 2005; Subasinghe, 2005). There are numerous such examples that in recent years have resulted in tens of thousands of lost jobs, billions of dollars in direct loss, and collapse of economies reliant on aquatic animal production, particularly in developing countries (Brummett et al., 2014). The introduction of the infectious salmon anaemia (ISA) virus into Chilean salmon farms (Asche et al., 2009), the emergence of bacterial disease, such as acute hepatopancreatic necrosis disease (AHPND) in shrimp farms in a number of Asian countries (FAO, 2013) and spread of white spot syndrome (WSS) virus to shrimp farms in two countries bordering the Mozambique channel (World Bank/RAF, 2013; FAO, 2015), underscore the vulnerability of aquaculture farming (Brummett et al., 2014; Oidtmann et al., 2011).
Such disease outbreaks have the potential of seriously compromising investment in future aquaculture development.
Exotic disease incursions do not only affect aquaculture; they may also pose serious risk to natural fish stocks. The important role of ornamental fish in transmitting disease is well illustrated by epidemics of koi herpesvirus disease in cultured and wild carp populations in Indonesia following introduction of the disease in 2002 (Sunarto, Rukyani and Itami, 2005). Other poorly managed pathways of disease transmission may involve spread from non-native food stocks (live, fresh or frozen material) used in aquaculture as in the case of pilchard herpesvirus that decimated wild Australian pilchard stocks following the introduction of the disease into these waters in the late 1990s (Whittington, Jones and Hyatt, 2005). Wild populations of aquatic animals may harbour diseases and act as reservoirs for infection in cultured stocks.
This is particularly relevant to shrimp and marine finfish (Bondad-Reantaso et al., 2005). Interactions between wild and cultured populations are thus of particular concern for aquaculturists and natural resource conservation officers.
Movement of live aquatic animals, within and between countries, associated with aquaculture, marketing of live aquatic animals, and the ornamental fish trade is an increasingly important route of pathogen spread (Oidtmann et al., 2011). Advances in trade in live aquatic animals and the efficiency of modern transportation methods have created opportunities for highly contagious transboundary aquatic animal diseases (TAADs), that have the potential to cause serious socioeconomic impact and to spread rapidly across national borders (Baldock, 2002; Bondad-Reantaso, 2004; Subasinghe, 2005; Rodgers, Mohan and Peeler, 2011). Once a pathogen becomes established within the natural ecosystem, treatment and eradication may become virtually impossible (Hine et al., 2012).
In recent years, the emergence of koi herpesvirus, a highly contagious disease of carp (Cyprinus carpio); epizootic ulcerative syndrome (EUS), an oomycete infection that affects a wide range of fresh and brackish-water finfish; and ISA, a serious viral disease of Atlantic salmon, have had a major impact on finfish production in various parts of the world where these diseases previously did not occur. Among invertebrate aquatic animals, the emergence of the viral diseases of shrimp: white spot syndrome, yellow head disease and Taura syndrome; and in bivalves: the parasitic disease Bonamia ostreae and the ostreid herpesvirus have led to enormous financial losses and socioeconomic disruptions in affected countries (Bondad-Reantaso et al., 2005; Oidtmann et al., 2011).
For aquaculture development to remain sustainable, wherever possible, timeous measures need to be applied to prevent transfer and introductions of aquatic animal pathogens and to limit the consequences of disease outbreaks (Hine et al., 2012).
The development and implementation of biosecurity and zoning strategies is increasingly recognized by countries and industries as essential to sustainable growth in aquaculture (Håstein et al., 2008; Hine et al., 2012). One of the strongest incentives for implementing national biosecurity programmes is the ability to move and trade aquatic animals and their products free of specific pathogens (Håstein et al., 2008). This requires international recognition of a country’s ability to demonstrate effective biosecurity and zoning strategies, including the ability to maintain zones and compartments of known disease status.