All Diseases

Covert Mortality Disease

Covert Mortality Disease, Covert Mortality Nodavirus Disease, or viral covert mortality disease is a shrimp disease caused by Covert Mortality Nodavirus. This disease commonly infects seawater and brackish water shrimp.

Indication of Disease

Name

Covert Mortality Disease

Clinical signs

When shrimp die, they fall to the bottom of the pond instead of floating on the surface of the water. The virus’ infection causes the core of hepatopancreas cells to expand, as well as muscle cell necrosis, indicated by the shrimp’s body that turns white, similar to Myo signs. Shrimp's digestive track turns golden brown, their stomach is empty, their shell softens, their growth slows, and their abdominal muscles fade in color.

Method of diagnosis

Can be tested using real-time PCR.

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Pathogen

Name

Nodavirus

Pathogen type

Virus

Synonyms

  • Cover Mortality Nodavirus (CMNV)
  • Viral Covert Mortality Disease (VCMD)

Characteristics

This virus has a capsid and an average diameter of 25-32 nm.

Pathogen Effect

Toxicity

The mortality or death rate of shrimp increases between 80-90%, 60-80 days after stocking the fry.

Predispositional factors

No data

Transmission

This virus may transmit vertically from broodstock to offspring. Furthermore, the virus can infect several invertebrates commonly found in ponds, including Artemia sinica, Balanus sp. (barnacle), Brachionus urceus (rotifera), Corophium sinense (amphipod), Crassostrea gigas (oyster), Diogenes edwardsii (hermit crab), Meretrix lusoria (mussel), Ocypode cordimundus (ghost crab), Parathemisto gaudichaudi (amphipod), and Tubuca arcuata (crab).

Epidemiology

It appeared in China in 2002-2003 and remained an epidemic disease for around ten years.

Host or vector

It is not yet known if those invertebrates are pure vectors or simply infected.

Infectious dose

No data

Incubation period

Occurs 60-80 days after stocking.

Stability and Viability

Susceptibility to drugs

No information

Susceptibility to disinfectants/probiotics

There is no vaccine or probiotics for this virus yet

Physical inactivation

No information

Handling and Prevention

Early warning

Observing clinical signs that appear on shrimp, including soft shells, slow growth, and pale body color, particularly in the muscles of the abdominal segments.

Prevention

There is currently no known way to prevent this virus

Treatment

There is currently no known way to treat this virus

Eradication

If infected by this virus, shrimp must be isolated and killed by heating to 70°C.

Regulation and Other Information

There are no regulations or further information regarding this virus.

References

Liu, S., Wang, X., Xu, T., Li, X., Du, L., Zhang, Q. 2018. Vectors and reservoir hosts of covert mortality nodavirus (CMNV) in shrimp ponds. Journal of Invertebrate Pathology. doi: 10.1016/j.jip.2018.03.011

PubMed.gov. A new nodavirus is associated with covert mortality disease of shrimp.

Qingli Zhang, Qun Liu, Shuang Liu, Haolin Yang, Sun Liu, Luoluo Zhu, Bing Yang, Jiting Jin, Lixue Ding, Xiuhua Wang, Yan Liang, Qintao Wang and Jie Huang. 2014. A new nodavirus is associated with covert mortality disease of shrimp. Journal of General Virology. 95, 2700–2709.

Thitamadee, S., Prachumwat, A., Srisala, J., Jaroenlak, P., Salachan, P.V., Sritunyalucksana, K., Flegel, T.W., Itsathitphaisarn, O. 2016. Review of current disease threats for cultivated penaeid shrimp in Asia. Aquaculture 452 69-87. doi: 10.1016/j.aquaculture.2015.10.028

Virus Research. Prevalence. And distribution of covert mortality nodavirus (CMNV) In cultured crustacean.