Taura Syndrome - Diagnostic Methods

Diagnostic Methods

A presumptive diagnosis of acute TSV infection can be established by the presence of dead or dying shrimp in cast nets used for routine evaluation. Predatory birds are attracted to diseased ponds and feed heavily on the dying shrimp. The unique signs of infection caused by TS, such as the cuticular melanized spots, can provide a strong presumptive diagnosis, but care must be taken as these can be confused with other diseases, such as bacterial shell disease. In general pathognomonic histopathological lesions are the first step in confirmatory diagnosis. Discrete foci of pyknotic and karyorhectic nuclei and inflammation are seen within the cuticular tissues. The lymphoid organ might display spheroids, but is otherwise unremarkable.

The genome of the virus has been cloned and cDNA probes are available for diagnosis. Reverse transcriptase polymerase chain reaction (RT-PCR) methods have been developed for detection of TSV and are very sensitive. Real-time techniques allow for quantification of the virus. The IQ2000TM TSV detection system, a RT-PCR method, is said to have a detection limit of 10 copies per reaction.

RNA-based methods are limited by the relative fragility of the viral RNA. Prolonged fixation in Davidsons' fixative might result in RNA degradation due to fixative-induced acid hydrolysis. An alternative for virus detection is the use of specific monoclonal antibodies (MAbs) directed against the relatively stable proteins in the viral capsid. Rapid diagnostic tests using MAbs are now in common use for white spot syndrome virus and are being marketed under the commercial name of Shrimple. Similar tests for TSV, yellowhead virus and infectious hypodermal and haematopoietic necrosis virus are currently under development.