Gene expression kinetics of the yellow head virus in experimentally infected Litopenaeus vannamei

The yellow head virus (YHV) has been reported to be one of most pathogenic viruses for cultivated shrimp; however, serious problems have only been reported in farms in south and southeastern Asian. Recently, a YHV strain was detected in Litopenaeus vannamei cultivated in Mexican farms that lacked virus-associated mortalities or epizooties, and the animals were apparently healthy. The identity of the virus was confirmed by sequencing replicative and structural protein-encoding regions and comparing with homologous virus sequences. Phylogenic relationships and genetic distances were also determined and, although some differences were observed, an influence on virulence was uncertain. In addition, the expression levels of several transcripts (3CL^PRO, POL, GP64 and GP116) were evaluated by quantitative real-time polymerase chain reaction during an experimental infection. Although the transcript showed varying kinetics, viral genes were expressed in infected L. vannamei, demonstrating the replicative capability of this YHV strain.