Yellow Head Disease (YHV) in Shrimp: A Disease Guide

Yellow head virus causes rapid mass mortality in farmed shrimp, with a yellowing swollen cephalothorax. There is no treatment; control relies on SPF stock and biosecurity.

Overview

Yellow head disease (YHD) is one of the most devastating viral diseases of farmed penaeid shrimp. It is caused by yellow head virus genotype 1 (YHV1), an enveloped, positive-sense single-stranded RNA virus of the genus Okavirus, family Roniviridae, order Nidovirales. The closely related gill-associated virus (GAV) belongs to the same YHV complex. First reported from Thailand around 1990, YHD spread through Asian shrimp farming and is a notifiable disease of the World Organisation for Animal Health (WOAH).

Affected species

The main host is the giant tiger prawn, Penaeus monodon, with disease often seen in juveniles around 50-70 days into the production cycle. Other penaeids, including Penaeus vannamei (Litopenaeus vannamei), Penaeus merguiensis, Penaeus setiferus, and Penaeus stylirostris, can also be infected. Because outbreaks progress so quickly, YHD can destroy a crop within days of the first signs.

Clinical signs

• A brief period of unusually high feeding that ends abruptly
• Cessation of feeding and lethargy
• Yellowing and swelling of the cephalothorax and underlying hepatopancreas
• Pale or bleached overall body coloration
• Affected shrimp gathering near the pond surface and edges
• Rapid onset of mass mortality

Transmission

YHV spreads horizontally through the water, by direct contact, and by cannibalism of dead or moribund infected shrimp. The movement of live infected shrimp and contaminated water between facilities is an important route of introduction. The virus is highly contagious, which is why an outbreak can move through a pond extremely fast.

Diagnosis

Diagnosis is confirmed by RT-PCR, supported by histopathology, in which infected tissues show intensely basophilic cytoplasmic inclusions. Because the gross signs can resemble other acute shrimp diseases, and because genotype identification matters for the YHV complex, laboratory confirmation is essential.

Treatment, control and prevention

There is no treatment for yellow head disease. Management depends entirely on excluding the virus and on biosecurity and pond management.

• Stock specific-pathogen-free (SPF) and PCR-screened postlarvae from certified hatcheries
• Screen broodstock and incoming animals and avoid YHV-positive sources
• Disinfect ponds, equipment, and incoming water; control carriers and vectors
• Remove and properly dispose of dead and moribund shrimp to limit cannibalism-driven spread
• Follow WOAH surveillance and movement-control requirements