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White Tail Disease

What is it?

White tail disease (WTD) or white muscle disease (WMD) is defined as a viral infection caused by Macrobrachium rosenbergii nodavirus (MrNV) and its associate extra small virus (XSV).

They cause a milky whitish appearance in larvae/postlarvae (PL)/early juveniles, and are responsible for large-scale mortalities in the freshwater prawn M. rosenbergii.

Where and When Might it Occur?

The disease was first reported in the French West Indies. It has since been seen in China, India and Thailand.

Not much is known about environmental factors that may cause an outbreak. However, outbreaks of WTD may be induced by rapid changes in salinity, temperature and pH.

Diagnosis

Infected PL become opaque and develop a whitish appearance, particularly in the abdominal region. The whitish discoloration appears first in the second or third abdominal segment and gradually diffuses both anteriorly and posteriorly.

Infected PL may also show progressive weakening of their feeding and swimming ability.

In severe cases, degeneration of telson and uropods may occur. Mortality may reach a maximum in about five days after the appearance of the first gross signs.

The disease has a variable mortality rate reaching up to 95 per cent.

Very few post-larvae presenting these signs survive and survivors seem to grow normally in grow-out ponds.

Control/Treatment

No work has been carried out on control and prevention of WTD. However, proper preventive measures, such as screening of brood stock and PL, and good management practices may help to prevent WTD in culture systems.

As the life cycle of M. rosenbergii is completed under controlled conditions, specific pathogen free (SPF) brood stock and PL can be produced by screening using sensitive diagnostic methods such as reversetranscription polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA)

Source: OIE