Detection of Taura syndrome virus (TSV) strain differences using selected diagnostic methods: diagnostic implications in penaeid shrimp

Anecdotal industry reports of Taura syndrome (TS) epizootics in a Taura syndrome virus (TSV) tolerant strain of Penaeus stylirostris and collected evidence of field TS epizootics in P. stylirostris suggested that a distinct new TSV strain might have emerged since 1994, The Ecuadorian 1992 TSV genome published in GenBank is virtually identical to the Hawaiian 1994 TSV isolate (HI94TSV) used as reference throughout this investigation. Three other geographic and year isolates of TSV from naturally occurring TS epizootics of cultured penaeid shrimp were obtained from Mexico (SIN98TSV and MX99TSV from P. vannamei and SON2KTSV from P. stylirostris). Selected TSV diagnostic methods set forth by the Office International des Epizooties were utilized as the basis for isolate analysis. By Southern blot, TSV probes P15 and Q1 reacted specifically with all the diagnostic reverse transcription polymerase chain reaction (RT-PCR) fragments. Additionally, labeled RT-PCR amplicons from the TSV isolates amplified by routine diagnostic RT-PCR primers gave positive in situ hybridizations with TSV, indicating that all 4 isolates shared homology. By Western blot, immuno-dot blot, and immunohistochemistry, all TSV-purified isolates reacted with TSV polyclonal antibody (PAb). However, with TSV monoclonal antibody (MAb) 1A1 all isolates, except SIN98TSV, reacted, indicating that the difference in isolate SIN98TSV is within VP1, the target for MAb 1A1 The amino acid (AA) sequence of SIN98TSV VP1, MX99TSV VP1 and SON2KTSV VP1 has a 98% homology with the reference H194TSV VP1. A span of 12 AAs are identified in SIN98TSV VP1 containing significant AA substitutions which may account for a conformational change of the antigenic epitope sufficient to prevent MAb 1A1 from binding. The implications of these results with respect to the antibody-based diagnosis of TSV are discussed.