TaqMan real-time and conventional nested PCR tests specific to yellow head virus genotype 7 (YHV7) identified in giant tiger shrimp in Australia

Abstract

In 2013, a unique seventh yellow head virus genotype (YHV7) was detected in Black Tiger shrimp (Penaeus monodon) broodstock that suffered high mortality following their capture from Joseph Bonaparte Gulf (JBG) in northern Australia. To assist with its diagnosis and assessment of its distribution, prevalence and pathogenicity, YHV7-specific TaqMan real-time qPCR and conventional nested PCR primer sets were designed to ORF1b gene sequences divergent from the other YHV genotypes. Using high (≥108) copies of plasmid (p)DNA controls containing ORF1b gene inserts of representative strains of YHV genotypes 1–7, both PCR tests displayed specificity for YHV7. Amplifications of serial 10-fold dilutions of quantified YHV7 pDNA and synthetic ssRNA showed that both tests could reliably detect 10 genome copies. Pleopods/gills from wild P. monodon sourced from locations in geographically disparate regions across northern Australia as well as 96 juveniles (48 either appearing normal or displaying signs of morbidity) from a commercial pond experiencing mortalities were screened to partially validate the diagnostic capacity of the qPCR test. Based on these data and PCR primer/probe sequence mismatches with other newly identified YHV genotypes, both YHV7-specific PCR tests should prove useful in the sensitive detection and discrimination of this genotype from YHV 2 (gill-associated virus) and YHV6 that can occur in Australian P. monodon, as well as from YHV genotypes currently listed as exotic to Australia.