Taura Syndrome (TSV) in Shrimp: A Disease Guide

Taura syndrome virus causes high mortality in farmed Penaeus vannamei, progressing through acute, transition, and chronic phases. There is no treatment; resistant lines are key.

Overview

Taura syndrome (TS) is a serious viral disease of farmed penaeid shrimp caused by Taura syndrome virus (TSV), a small, non-enveloped, icosahedral, positive-sense single-stranded RNA virus about 31-32 nm in diameter, classified in the family Dicistroviridae and described as picornavirus-like. First identified in 1992 near the Taura river in Ecuador, the virus spread rapidly through the shrimp-farming Americas and is a notifiable disease of the World Organisation for Animal Health (WOAH).

Affected species

The principal host is the Pacific white shrimp, Penaeus vannamei (Litopenaeus vannamei), which suffers the most significant outbreaks and mortality, especially at postlarval, juvenile, and early adult stages. Other penaeids, including Penaeus stylirostris, Penaeus setiferus, and Penaeus schmitti, can also be infected. The disease has caused very large economic losses across the Americas since its emergence.

Disease phases and clinical signs

Taura syndrome typically progresses through three phases. In the acute phase, affected shrimp show anorexia, lethargy, soft cuticle, an empty gut, and a characteristic red coloration of the tail fan and appendages from expansion of the chromatophores; mortality during moulting can be very high. The transition phase is marked by multifocal melanized (brown to black) lesions in the cuticle. Survivors enter the chronic phase, in which they remain persistently infected, often for many months and possibly for life, with no obvious clinical signs.

• Acute: reddish tail fan and appendages, soft shell, anorexia, lethargy, high moult-associated mortality
• Transition: randomly distributed melanized cuticular lesions
• Chronic: persistently infected carriers without obvious external signs

Transmission and diagnosis

TSV spreads horizontally through water and through cannibalism of dead or moribund infected shrimp, and it can be moved mechanically between farms by seabirds and aquatic insects. Diagnosis in the acute phase relies on histopathology of the cuticular epithelium, which shows pathognomonic multifocal necrosis with pyknotic and karyorrhectic nuclei giving a peppered or buckshot appearance; in the transition and chronic phases, molecular methods such as RT-PCR and gene probes are needed.

Treatment, control and prevention

There is no treatment for Taura syndrome. Its control is one of the clearest success stories of shrimp health management, achieved largely through genetics and biosecurity.

• Stock specific-pathogen-free (SPF) postlarvae and screen broodstock
• Use specific-pathogen-resistant (SPR) selected lines, which have reached high or near-complete resistance to some TSV variants
• Disinfect ponds and equipment and control crustacean and vector access
• Remove and dispose of dead and moribund shrimp to limit cannibalism-driven spread
• Follow WOAH surveillance and movement-control requirements