"Yellow head disease is caused by the yellow head virus (YHV). This important disease affects Penaus monodon farms in Thailand. In Mexico, reports of this disease in L. vannamei have been issued. This has not been officially declared by the World Organization for Animal Health (OIE). This study reports a method of reverse-transcription polymerase chain reaction for the detection of this virus in shrimp. A certified sample was analyzed with a commercial detection system for YHV. We obtained a differential sequence of genotypes that cause both YHV and gill-associated virus (GAV) by comparison with ClustalW. Primers were designed for amplification of the fragment by a TaqMan probe with which a positive standard to YHV was amplified. Tests were negative for other pathogens. A survey of shrimp farms in Mexico in 2009 showed negative results for YHV presence. These results demonstrate that the system developed in this study is a specific diagnostic method, sensitive and reproducible for detection of YHV."