The study, published in Diseases of Aquatic Organisms, confirmed the tests are highly accurate, reliable and fit for purpose. This provides confidence for import authorities and the prawn industry, when establishing Australia’s freedom from white spot syndrome virus.
White spot syndrome virus causes white spot disease in prawns and can infect a wide range of decapod crustaceans. These include crabs, lobsters, prawns, shrimp and crayfish. It is an internationally notifiable disease and is a serious threat to the aquaculture industry worldwide.
In prawn farm operations white spot can kill all prawns at a farm within a few days of the onset of visible signs of the disease.
Australia was free from white spot disease until, in December 2016, white spot syndrome virus was detected in a prawn farm in South-East Queensland.
Australia’s national reference laboratory
When an emergency animal disease is detected, Australia's state and national agencies work together to test samples, contain the disease and manage a coordinated response.
Our Australian Centre for Disease Preparedness (ACDP) is Australia’s national reference laboratory. In this role, ACDP has primary responsibility for confirmation or exclusion of notifiable diseases in samples sent from outbreak regions.
During the outbreak of white spot disease in South-East Queensland’s prawn farms, and subsequent surveillance activities, the lab used two PCR tests, one recommended by the World Organisation of Animal Health (WOAH) and the other published by CSIRO scientists.
Scientists from ACDP tested over 25,000 samples for the presence or absence of white spot syndrome virus, from 2016 to 2020.
While the tests used were the best available, scientists from ACDP’s Fish Diseases Laboratory knew some important characteristics about test performance were missing and decided to validate these two tests according to WOAH standards, with funding from the Australian Government Department of Agriculture, Fisheries and Forestry.
Working with the Collaborating Centre for Diagnostic Test Validation Science in the Asia-Pacific Region
WOAH sets international standards for validating tests, which require scientists to provide evidence that tests perform effectively, as expected and are fit for purpose.
ACDP, in partnership with Melbourne University and Massey University, is the WOAH Collaborating Centre for Diagnostic Test Validation Science in the Asia-Pacific Region.
Part of a collaborating centre’s role is to develop or improve diagnostic tests, with the aim of creating tests that meet international standards. So our scientists got working to validate the two WSSV real-time PCR tests.
Determining test sensitivity and specificity
With access to the large amount of testing data collected during WSSV outbreaks, our scientists worked together with colleagues at the University of Prince Edward Island to undertake the validation process. This determined several key performance characteristics that were not previously known.
Two important test characteristics are diagnostic sensitivity, a measure of how often truly diseased animals will indeed test positive, and diagnostic specificity, which is a measure of how often truly non-diseased animals will test negative. These two test characteristics are important when designing effective surveillance activities, particularly in apparently healthy animals.
The study found both the WOAH and CSIRO PCR tests are highly accurate for detecting white spot syndrome virus in samples from apparently healthy prawns.
The entire process of validation has been published in the peer reviewed journal Diseases of Aquatic Organisms. The new performance characteristics from this work have since been incorporated into current updates of the Australian and New Zealand Standard Diagnostic Procedure for white spot syndrome virus and the WOAH Aquatic Manual Chapter for infection with white spot syndrome virus.