Surveillance and risk assessment for early detection of emerging infectious diseases in livestock

Those who work in the area of surveillance and prevention of emerging infectious diseases (EIDs) face a challenge in accurately predicting where infection will occur and who (or what) it will affect. Establishing surveillance and control programmes for EIDs requires substantial and long-term commitment of resources that are limited in nature. This contrasts with the unquantifiable number of possible zoonotic and non-zoonotic infectious diseases that may emerge, even when the focus is restricted to diseases involving livestock. Such diseases may emerge from many combinations of, and changes in, host species, production systems, environments/habitats and pathogen types. Given these multiple elements, risk prioritisation frameworks should be used more widely to support decision-making and resource allocation for surveillance. In this paper, the authors use recent examples of EID events in livestock to review surveillance approaches for the early detection of EIDs, and highlight the need for surveillance programmes to be informed and prioritised by regularly updated risk assessment frameworks. They conclude by discussing some unmet needs in risk assessment practices for EIDs, and the need for improved coordination in global infectious disease surveillance.

A new approach to the management of emerging diseases of aquatic animals

Since 1970, aquaculture has grown at a rate of between 5% and 10% per annum. It has achieved this by expanding into new areas, farming new (often non-native) species and intensifying production. These features of aquaculture, combined with large-scale movements of animals, have driven disease emergence, with negative consequences for both production and biodiversity. Efforts to improve the management of emerging diseases of aquatic animals must include actions to reduce the rate of disease emergence, enhance disease detection and reporting, and improve responses to prevent disease spread. The rate of disease emergence can be reduced by understanding the underpinning mechanisms and developing measures to mitigate them. The three principal mechanisms of disease emergence, namely, host switching, decreased host immunocompetence and increased pathogen virulence, have many drivers. The most important of these drivers are those that expose susceptible hosts to novel pathogens (e.g. the introduction of non-native hosts, translocation of pathogens, and increased interaction between wild and farmed populations), followed by host switching. Exposure to wild populations can be reduced through infrastructure and management measures to reduce escapes or exclude wild animals (e.g. barrier nets, filtration and closed-confinement technology). A high standard of health management ensures immunocompetence and resistance to putative new pathogens and strains, and thus reduces the rate of emergence. Appropriate site selection and husbandry can reduce the likelihood of pathogens developing increased virulence by preventing their continuous cycling in geographically or temporally linked populations. The under-reporting of emerging aquatic animal diseases constrains appropriate investigation and timely response. At the producer level, employing information and communications technology (e.g. smartphone applications and Cloud computing) to collect and manage data, coupled with a farmer-centric approach to surveillance, could improve reporting. In addition, reporting behaviours must be understood and disincentives mitigated. At the international level, improving the reporting of emerging diseases to the World Organisation for Animal Health allows Member Countries to implement appropriate measures to reduce transboundary spread. Reporting would be incentivised if the global response included the provision of support to low-income countries to, in the short term, control a reported emerging disease, and, in the longer term, develop aquatic animal health services. Early detection and reporting of emerging diseases are only of benefit if Competent Authorities' responses prevent disease spread. Effective responses to emerging diseases are challenging because basic information and tools are often lacking. Consequently, responses are likely to be sub-optimal unless contingency plans have been developed and tested, and decision-making arrangements have been well established.

The aquatic animal pandemic crisis

The growth of aquaculture over the past 50 years has been accompanied by the emergence of aquatic animal diseases, many of which have spread to become pandemic in countries or continents. An analysis of 400 emerging disease events in aquatic animals that were logged by the Centre for Environment, Fisheries and Aquaculture Science between 2002 and 2017 revealed that more than half were caused by viruses. However, in molluscs, most events were parasitic. Categorising these events indicated that the key processes underpinning emergence were the movement of live animals and host switching. Profiles of key pathogens further illustrate the importance of wild aquatic animals as the source of new infections in farmed animals. It is also clear that the spread of new diseases through the largescale movement of aquatic animals for farming, for food and for the ornamental trade has allowed many to achieve pandemic status. Many viral pathogens of fish (e.g. infectious salmon anaemia, viral haemorrhagic septicaemia) and shrimp (e.g. white spot syndrome virus) affect a large proportion of the global production of key susceptible species. Wild aquatic animal populations have also been severely affected by pandemic diseases, best exemplified by Batrachochytrium dendrobatidis, a fungal infection of amphibians, whose emergence and spread were driven by the movement of animals for the ornamental trade. Batrachochytrium dendrobatidis is now widespread in the tropics and subtropics and has caused local extinctions of susceptible amphibian hosts. Given the rising demand for seafood, aquacultural production will continue to grow and diseases will continue to emerge. Some will inevitably achieve pandemic status, having significant impacts on production and trade, unless there are considerable changes in global monitoring and the response to aquatic animal diseases.

Vulnerabilities in aquatic animal production

The role of aquatic animals in global food and nutrition security is increasingly recognised. The global demand for fish is increasing, leading to a need to significantly increase its supply. Securing future fish supplies through sustainable production is a challenge as major resources such as fresh water and land are becoming limited worldwide. Aquaculture and capture fisheries face various threats from both human-mediated and natural environmental change, including climate change. Aquaculture systems and practices are vulnerable to such changes. Moreover, aquatic animal diseases are currently considered one of the most important constraints to sustainable global fish production. The need to increase global production, combined with climate change, may increase losses due to diseases. This paper examines key vulnerabilities, their impacts and management to achieve increased and sustainable global fish production. The authors focus on the need to apply international standards, and to develop biosecurity and capacity in aquatic animal health to improve global fish health. Research needed to underpin the development of improved detection and control of fish diseases is also discussed.

Emerging infectious disease risk: shared drivers with environmental change

Outbreaks of emerging infectious diseases (EIDs) seemingly appear without warning, severely exacerbating public and animal health burdens and spreading across borders. Since 1940, the rate of infectious disease emergence events has risen. Given the considerable economic and other societal costs associated with EIDs, understanding the specific drivers of these diseases and developing concrete measures to prevent and mitigate their spread is urgently needed in both health security and sustainable development discussions. Human modification of the environment serves as an underlying driver in EID risk: environmental change thus warrants consideration in surveillance and outbreak investigations to identify the origin of the disease and contribute to the development of effective actions to prevent, prepare for or reduce the risk of future events. Coordinated approaches to address the underlying and, in some cases, overlapping causes of both disease emergence and global environmental change may yield benefits for sustainable and healthy solutions to meet or reshape the demands of a growing global population and contribute to global health security.

Preparedness activities and research needs in addressing emerging infectious animal and zoonotic diseases

Emerging infectious animal and zoonotic diseases can inflict significant losses on animal production and public health, and threaten the safety and security of the food system. Threat analysis (forecasting), which monitors the measurable risk indicators of disease emergence, should be in place before the emergence of any threat. Animal and public health authorities develop and regularly re-evaluate disease preparedness, response and recovery plans, based on the 'One Health' principle. These plans should include surveillance, biosecurity measures, communication channels and training for personnel. Scenarios for outbreaks of natural emerging infectious disease or bioterrorist events should be prepared and practised. National and international legislation should be regularly updated to provide a robust legal basis to manage outbreaks. Reference laboratories should have reliable and validated diagnostic tools for rapid, high-throughput testing. Strict biosafety, biocontainment and biosecurity control measures must be implemented in laboratories in order to prevent the accidental or malicious release of pathogens. The pharmaceutical industry should be incentivised to develop vaccines and/or antiviral drugs against disease outbreaks. Conventions between public authorities and the pharmaceutical industry should guarantee adequate stockpiling of the pharmaceuticals needed to control large-scale outbreaks. In the early phase of disease emergence (early warning), veterinarians and stakeholders play an important role in early detection at the farm level. Upon notification, veterinary authorities must take rapid response measures to limit disease spread. National and international short- and medium-term strategic research agendas should be developed, based on a comprehensive gap analysis and horizon scan. This planning will help to guide funding agencies and non-governmental organisations in their quest to support relevant research.