Yellow head disease

Yellow head disease (YHD) appears on black tiger prawn, whiteleg shrimp and many other types of shrimp in Vietnam, Thailand, or India. In Vietnam, shrimp is often infected with yellow head disease due to changes in weather, seasons, and in coastal areas with high salinity.

Symptoms:

- Shrimp eats unusually for a few days then suddenly stops eating. After 1-2 days, shrimp swims lethargically without direction on the water surface or along the shore; shrimp clinging to the shore.
- The cephalothorax, liver, and pancreas of shrimp turn yellow; the liver may be pale white, light yellow or brown.
- Shrimp body is pale.
- Shrimp dies scattered in feeding tray and then dies with an increasing rate.
- Shrimp dies very quickly within 3-5 days (maybe almost 100%) after the appearance of symptoms.
- According to Viet Linh, the disease aggravates and causes rapid death when shrimp shows signs of infection with both yellow head disease and white spot disease.

Yellow head disease in black tiger shrimp (Penaeus monodon). On the left: infected shrimp. On the right: healthy shrimp. Source: DV Lightner - Enaca

Methods of diagnosis:

- Recognize and identify symptoms of the disease.
- Tissue staining, blood cells show that the cell nucleus is degenerated and coagulated.
- PCR analysis.

Causes:

- Yellow head virus (YHV) is a rod-shaped, single-stranded RNA virus with size 44 x 173 nm, belonging to the species Nidovirales, family Ronaviridae, genus Okavirus.

Disease transmission:

- Mainly horizontal transmission, due to an intermediate host carrying pathogens into the farming environment.

Preventions and treatments:

- Yellow head disease has no cure.
- Prevention and control by selecting disease-free shrimp seed (through PCR testing), disinfecting ponds to kill bacteria and pathogens in water.
- Do not farm with too high density.
- Always provide enough oxygen for the pond.
- Keep the environment stable.