Issues Magazine

Emerging Diseases: Where Are We Now?

By Brian Jones and Martyn Jeggo

Two members of a 2004 think tank look back to see how Australia has responded since this meeting to the ever-increasing risks from emerging diseases, in particular to aquaculture.

In 2004, a “high flyers” think tank, held in Brisbane and organised by the Australian Academy of Science, examined the issue of biosecurity in Australia. Under the heading “Emerging Diseases – Ready and Waiting”, the meeting was divided into four categories: human health, animal health, plant health, and aquatic health. Perhaps ahead of its time, this think tank took a broad approach both to bringing together health experts from across the various species at risk, including humans, and reached conclusions that essentially embraced what is today commonly known as the “one health” approach*. “One health” refers to the inextricable link between human health and animal health, and the need for interdisciplinary collaboration and communication across the public health, agricultural and environmental sectors for effective management of the threats from emerging infectious diseases.

A central theme of the think tank’s deliberations was the establishment of an Australian Centre for Disease Control (ACDC) along similar lines to the Centres for Disease Control (CDC) based in Atlanta, Georgia, USA, which provides regional support across the Americas.

There have certainly been a number of high-profile “emerging diseases” since 2004 – including swine flu, equine influenza, Hendra and abalone viral ganglioneuritis – but we have made significant improvements in responding to and managing emerging disease risks. In 2004, Australia was seen by its trading partners as being among the best prepared countries in terms of managing emerging diseases, and that is still clearly the case today.

What has emerged over the past few years has been an increasing focus on those diseases that cross the species barriers, and particularly those that threaten both humans and animals. Importantly, some 75% of new infectious diseases in humans come from animals and in managing these it is crucial to adopt a “one health” approach. Since 2004 there has been an ever-increasing level of collaboration between those working in human health, with counterparts in livestock health management. This cooperation extends from the research area to disease management and emergency response.

During this time two critical reviews have also been undertaken by the federal government to ensure that Australia is responding appropriately to the emerging infectious disease risks. In 2008, following the equine influenza outbreak – the largest single infectious disease outbreak in the history of Australia – the Beale review was commissioned (see p.11). This review looked at all aspects of biosecurity, except those dealing directly with human health. It made some 184 recommendations, and critically saw a need to reorganise at the Commonwealth level to ensure a full integration across the various agricultural industries.

The review identified a need to link management of the environment with biosecurity and the need to consider activities as a continuum from pre-border to border and post-border within Australia – issues that were discussed at the Australian Academy of Science think tank in 2004. Like the think tank, the Beale review identified the need for a “one health” approach; it saw the need reorganise to manage the increasing risks, and it recognised the trans-boundary nature of the risks.

The second review in 2009 was the commissioning of a Prime Minister and Cabinet working group on the threat from emerging infectious diseases (see www.innovation.gov.au/ScienceAndResearch/prime_ministers_science_enginee...

EpidemicsWGReport.pdf). This group also recognised the ever-increasing risks from infectious diseases, and the need for a unified approach. A major recommendation called for the formation of an Australian Centre for Emerging Infectious Diseases to undertake the underpinning biosecurity research using a national collaborative and coordinated model. This recommendation mirrored the ACDC approach of the think tank in 2004.

In 2007, prior to these reviews, Australia established a National Biosecurity Committee to bring together environmental and agricultural biosecurity issues. The subsequent two government reviews added many enhancements to this new direction. Indeed the original concepts developed by the think tank have seen real change, and have helped to influence positive change. We will focus here on one sector, aquaculture, to gain further insight on the progress that has been achieved to improve Australia’s management of its biosecurity risks.

Aquatic industries are often overlooked when discussing primary production, but aquaculture is growing steadily and worldwide about 50% (up from 40% in 2004) of all fisheries products now come from aquaculture ventures ranging from small family units through to large multinational companies. In the future, most fisheries products eaten by Australians will come from aquaculture.

It is also not generally understood that the largest “fishery” industry services the recreational angler. Australians like to catch fish, and support an industry that in Western Australia alone is estimated to be worth in excess of $1 billion.

Ornamental fish are one of the major pet industries, with an annual value nationally of over $300 million. All of these activities pose unique biosecurity issues.

Unlike terrestrial industries, which tend to focus on a small group of well-understood imported production animals such as cows and sheep, most aquaculture species, both in Australia as well as overseas, tend to be native species that are relatively new to cultivation and subject to locally new and emerging diseases. This, coupled with a lack of veterinary services over most of the major aquatic production areas, movement of live aquatic animals internationally and a lack of vaccines and veterinary medicines, means that disease remains a major constraint to production.

The year 2004 saw the launch of AQUAPLAN 2005–2010, Australia’s National Strategic Plan for Aquatic Animal Health (see www.daff.gov.au/animal-plant-health/aquatic/aquaplan). The plan resulted in a concerted effort by both government and industry members to address deficiencies in aquatic animal disease and biosecurity preparedness. The outcomes of the five-year AQUAPLAN are currently being reviewed, and the decision whether to develop a new five-year plan will depend on the outcome of that review.

A major aquatic biosecurity initiative, taken independently of AQUAPLAN, has been the development of a national system for the prevention and management of marine pest incursions. This system was the outcome of work linking Australian outbreaks of paralytic shellfish poisoning, which is associated with shellfish consumption, to the introduction of the causative organisms via ballast water in the 1980s. Surveys of ports have confirmed that over 250 marine species have been introduced to Australia since colonial days, and many of these are thought to have come either in ballast water or as hull-fouling organisms on ships. A few of these organisms are now serious pests, so the aim of the national system is to develop programs to prevent, watch for and respond to pest incursions anywhere in Australia through a shared funding arrangement between the jurisdictions (see www.marinepests.gov.au). Australia is now taking a lead role in international efforts to manage the spread of marine pests through shipping.

Back in 2004 it was identified that there was an increased need for aquatic industries to adopt good “on farm” biosecurity measures rather than relying on “at border” interception of pathogens. This is still progressing, with the World Organisation for Animal Health (OIE) recently recognising the concept of biosecurity at the farm level (the “compartment”) as a valid basis on which to adopt international trade certification for movement of product between countries. This concept was included as part of AQUAPLAN, but getting Australian farms to adopt such an approach remains a challenge.

However, international standards for disease control are still based on the concept of controlling the pathogen. These standards arose before World War I to protect the terrestrial industries from movement, by sea, of animal diseases between the colonies. The principle is that trade can only be restricted if it can be shown that the pathogen of concern is either absent, or is controlled, within the destination country. The pathogen does not have to be causing disease – it is its presence that is important.

This concept of protecting only from a known pathogen of concern is being challenged by experience with aquatic diseases and increasing understanding of the molecular basis on which pathogen strain variation and virulence is based. New and emerging diseases can cause devastation long before the causative agent is identified. Examples of apparently infectious diseases where the agent is still unknown include Akoya oyster disease in Asia and pearl oyster oedema disease in Australia.

Abalone viral ganglioneuritis was identified in 2005 in Victoria, where it caused severe mortality to abalone over 200 km of marine reefs. It was apparently introduced accidentally from Tasmania at a time when the virus was unknown to science.

A similar pattern occurred in France, where massive mortalities of rock oysters have occurred annually since 2007. The French have in 2009 finally identified the cause of their problems as a new virulent strain of oyster herpes virus, but not before French oysters, and the disease, were moved to Ireland.

A related problem to this movement of unknown pathogens is posed by the international trade in frozen shrimp, most of which are infected with a variety of internationally reportable viruses that survive freezing and that can end up being used as bait or fish feed, thus transmitting live exotic viruses to the environment. A conundrum that the OIE has so far failed to address is how any country (including Australia) with such frozen products on the supermarket shelf can continue to report “freedom” from the presence of the viruses contained in that product.

The ornamental fish trade is also a major risk to Australian fauna. A number of exotic pathogens have been introduced with the ornamental fish trade, and iridoviruses, which are a threat to native fish and frogs, are still coming into the country. Biosecurity Australia is currently re-evaluating the risk associated with the importation of certain types of ornamental fish.

In 2004, a lack of expertise in aquatic animal husbandry in these new and emerging industries was also identified. Although the problem has been well-documented since then, there has been little progress in implementing a solution. It has been estimated that over 60 species of aquatic animals have been trialled for aquaculture in Australia, and each comes with its own unique set of production and disease issues. Most of these are native species, and their parasites are also native species, so information needs to come from Australian research conducted here.

Finfish diseases are well-suited to control by vaccines, but although fish vaccines, in terms of doses, are now the largest market for veterinary vaccine companies worldwide, it is still usually financially unviable to get vaccines registered for sale in Australia since current policy requires that they be manufactured here. A review of the Australian Pesticides and Veterinary Medicines Authority is underway, but it is unlikely that vaccines produced overseas will be allowed for sale in Australia.

Back in 2004, immunology of aquatic invertebrates was mentioned as a major information gap. There were no immortal cell lines for any mollusc or crustacean, and our knowledge of immunology was rudimentary. The situation has not changed much. There are still no immortal cell lines and our understanding of invertebrate immunity is still rudimentary but is progressing rapidly, driven by advances in molecular techniques and genomics.

Even the paradigm that invertebrates have no acquired immunity has been challenged. In 2004 a search on the internet using “aquaculture and genomics” revealed about 100 papers and 3000 websites – that same search today would yield over 2000 papers and 15,000 websites on the same topic! It is more than likely that advances in science over the next five years will be bring huge changes to how we view new and emerging diseases.

Clearly, much has been undertaken to address the issues raised at the think tank in 2004, but it is also obvious that a great deal more is required. Nothing indicates that the threats from infectious disease will diminish, and whether they relate to a subsector of the aquaculture industry, to a livestock species or to humans we need to continue to allocate sufficient resources to ensure we have effective biosecurity mitigation strategies in place.