Shrimp diseases and current diagnostic methods

In less than 30 yr, the penaeid shrimp culture industries of the world developed from their experimental beginnings into major industries providing hundreds of thousands of jobs, billions of U.S. dollars in revenue, and augmentation of the world's food supply with a high value crop. Concomitant with the growth of the shrimp culture industry has been the recognition of the ever increasing importance of disease, especially those caused by infectious agents. Major epizootics have plagued the world's shrimp culture industries. The most important diseases of cultured penaeid shrimp have had viral or bacterial etiologies, but a few important diseases have fungal and protozoan agents as their cause. Diagnostic methods for these pathogens include the traditional methods of morphological pathology (direct light microscopy, histopathology, electron microscopy), enhancement and bioassay methods, traditional microbiology, and the application of serological methods. While tissue culture is considered to be a standard tool in medical and veterinary diagnostic labs, it has never been developed as a useable, routine diagnostic tool for shrimp pathogens. The need for rapid, sensitive diagnostic methods led to the application of modem biotechnology to penaeid shrimp disease. The industry now has modem diagnostic genomic probes with nonradioactive labels for viral pathogens like IHHNV, HPV, TSV, WSSV, MBV, and BP. Additional genomic probes for viruses, for bacterial pathogens like NHP and certain Vibrio spp., and Microsporidia have also been developed. Highly sensitive detection methods for some pathogens that employ DNA amplification methods based on the polymerase chain reaction (PCR) now exist, and more PCR methods are being developed for additional agents. These advanced molecular methods promise to provide badly needed diagnostic and research tools to an industry reeling from catastrophic epizootics and which must become poised to go on with the next phase of its development as an industry that must be better able to understand and manage disease.