Abalone are economically important species of molluscs, ranking fourth nationally and worth $190 million. These species have strong potential for future farming and ranching production development. However, with industry increasingly exploring live trade and developing new market access, infections with the parasite Perkinsus olseni can be a barrier for jurisdictions that have previously reported detection of Perkinsus sp. Overseas, Taiwan recently implemented a ban on live imports of abalone from Perkinsus-infected areas and this may be adopted by other countries in the future.
Perkinsus spp. have caused significant mortalities in commercially important mollusc species worldwide. Of these, the OIE listed pathogen, P. olseni, is the only species known to infect abalone in Australia. P. olseni has been reported from molluscs in NSW, VIC, SA, and WA. This parasite has been associated with mass mortality events and subsequent demise of blacklip abalone fisheries in NSW since the early 1990¶s (FRDC Project No. 2004/084). Recent investigations in greenlip abalone populations in Western Australia have revealed up to 80% prevalence and highly variable intensities of infection.
However, the investigation of the parasite dynamics and the associated risk factor(s) requires access to effective and efficient detection tools to measure the intensity of infection in an individual abalone and the prevalence of infection in large population surveys. These recent investigations have revealed severe analytical and diagnostic sensitivity and specificity deficiencies within the current protocols including the OIE one, and the various P. olseni strains present in Australia. The industry has highlighted the need for a reliable, rapid and specific method to detect this parasite at the species level (to date, 3 Perkinsus species have been described in Australia) in abalone tissues as well as in haemolymph, and water samples. This will lead to a better understanding of the prevalence and intensity of P. olseni infections on farm and in the wild, which will lead to the implementation of management measures. This lack of effective diagnostic tools is currently severely limiting Australia¶s capabilities to develop effective management
A complete reference genome for P. olseni from South Australia was generated as well as other P. olseni genomes for different geographical isolates and for P. chesapeaki from Queensland. This was the first time that the genomes of these two parasites were sequenced and they will provide invaluable insights into the physiology and origin of this parasite. They will also boost studies investigating host/parasite interactions and pathogenicity. The genomic data categorised the isolates into two groups based on their level of heterozygosity and gene content, with the Oceanian isolates (Australia and New Zealand) having a lower level of heterozygosity than the Eurasian isolates (Japan and Spain). With respect to the diagnostic methods, the internal transcribed spacer (ITS) region that is used for diagnostic tests worldwide, is repeated between 91 and 410 times in the P. olseni genome, which makes it a suitable region for presence/absence testing but unsuitable for quantification using qPCR to determine infection load of the parasite.
Two surface proteins classified as moonlighting proteins: an uncharacterised yet conserved hypothetical protein and a putative 60S ribosomal subunit protein L4, were common to all the P. olseni geographical isolates and were retained as candidates for antibody targets. Therefore, synthetic peptides from these proteins were produced and mice were immunised with these peptides. Mice were also immunised with whole P. olseni cells of the South Australian isolate. The immunisation process was repeated with three batches of mice over a two-year period resulting in the production of several antibodies specific to P. olseni, including different life stages of the parasite.