Improved diagnostic methods for endemic and exotic pathogens of aquatic animals have been identified as a Key Research Area in the 2009-12 FRDC AAHS R&D plan (6.2.3 Endemic and exotic aquatic animal disease diagnostics).

Since Perkinsus olseni was first described in Australian abalone by Lester and Davies in 1981, histology and culture in Ray’s medium have been the most commonly applied diagnostic procedures for detection of Perkinsus sp.. Although these tests are relatively straight forward and practical, they are general in nature and neither identifies or differentiates specific species of Perkinsus. Despite a well developed framework for the molecular characterization of Perkinsus and modern PCR based molecular tests for some of the more commercially important Perkinsus species, these have rarely been applied in Australia. The first attempts to apply molecular methods to a small number (n=40) of Perkinsus infected abalone from disease outbreaks in NSW have already revealed a new variant which probably represents a new previously unrecognized species in Australia (Reece et al. 2010). This fact and the apparent variation in pathogenicity observed with Perkinsus in different areas, has raised several questions about which Perkinsus sp. are present in commercial mollusc populations.

Given that a significant depletion of blacklip abalone (Haliotis rubra) stocks in NSW over the last 20 years has been attributed to infection with Perkinsus (FRDC Project 2004/084) and localized areas of infection occur in a number of Australian states, from South Australia to northern Western Australia, the development and implementation of highly sensitive and rapid PCR based molecular methods to identify specific species of Perkinsus is essential. The development and application of such tests is necessarily underpinned by a detailed understanding of the molecular makeup of Perkinsus in these populations which is the subject of this application.

Although the abalone and oyster industries and relevant jurisdictions have implemented a range of measures to mitigate the risks of major diseases of concern (i.e. AVG, POMS), both industry sectors still lack a nationally consistent, agreed approach to biosecurity.

An industry-wide biosecurity plan is a critical component of health accreditation programs to facilitate safe interjurisdictional and international trade in aquatic animals. Minimum biosecurity standards must meet importing jurisdiction or country requirements, so it is vital that these plans are recognised by state government authorities and implemented by industry. Note that for interstate trade, requirements generally outline that oyster or abalone livestock only be sourced from land-based facilities with high level (auditable) biosecurity.

The abalone industry require movement of broodstock between farms to improve genetic family lines. A national Abalone Health Accreditation Program (developed by SCAAH) provides guidance for land-based abalone farms to demonstrate freedom of AVG for the purpose of trade. Biosecurity and surveillance requirements form the basis of the health accreditation program. A nationally agreed biosecurity plan (guidance document) specific to land-based abalone farms, which identifies specific disease risks and provides recommended systems to mitigate those (and potential emergent) risks, is now required to assist farmers in developing their own farm biosecurity plans.

Similarly, for the oyster industry both biosecurity and surveillance are required to demonstrate freedom of POMS (and mitigation of potential other emergent biosecurity risks). This is particularly important for consideration of movement of hatchery reared spat (juveniles) from areas of known infection to areas not known to be affected by POMS. These two fundamental requirements (biosecurity and surveillance) are outlined in South Australia’s draft import protocols for spat sourced from oyster hatcheries. Nationally agreed guidelines for oyster hatchery biosecurity plans are now required to facilitate trade in oyster spat.

Diagnostic laboratories across the country vary in their diagnostic capability for aquatic animal pathogens. Due to their individual needs, many diagnostic laboratories have developed their own reagents and procedures for the identification of bacterial pathogens. This lack of standardisation can be problematical, for example, when reporting on aquatic animal health status. Using Vibrio identification as an example, it is likely that diagnostic laboratories would be capable of identification to the genus level (i.e. Vibrio sp.). However, due to differences in the various laboratories, identification to the species level would be difficult, and different laboratories are likely to use different procedures for identification.

There is a clear need for diagnostic scientists working in this area to compare and standardise protocols between States. A series of workshops aimed at providing training in the diagnosis of bacterial disease in aquatic animals for those new to the area, and at the same time providing an opportunity to evaluate the various diagnostic protocols used in Australia for their ability to identify both enzootic and exotic pathogens is overdue.

Development of Standard Diagnostic Techniques will require three logical steps:

1. Comparison and evaluation of the tests currently used by diagnostic laboratories;
2. Development of, and agreement on, the most sensitive, accurate and reproducible methods;
3. Adoption and publication of the agreed method for each pathogen as the Standard Diagnostic Technique.

Thus development of SDTs in aquatic animal bacteriology may include an SDT on general methods for aquatic animal bacteriology followed by SDTs for specific diseases such as Vibriosis. Vibriosis, due to its widespread occurence in vertebrate and invertebrate aquatic animal species in tropical and temperate regions of Australia, was identified as a disease of particular importance with respect to standardisation of diagnostic methods [1].

In order to ensure that the SDTs incorporate the latest technologies and information on exotic, as well as enzootic, bacterial pathogens, and that the SDTs will be recognised internationally as state-of-the-art, an international expert on the specific disease will be invited to participate in each of the respective workshops.

References

1. Fish Health Management Committee (1998). Report of the Fish Health Management Committee and the Fish Health Coordinating Group: Workshop on Aquatic Animal Health: Technical Issues, 7-9 December 1998, Melbourne, Victoria.