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Cause and Prevention of Infectious Myonecrosis in Litopenaeus Vannamei

Brief Introduction to Infectious Myonecrosis

 

Infectious myonecrosis (IMN) of penaeid shrimp is caused by infectious myonecrosis virus (IMNV). The first outbreak occurred in August 2002, where it appeared on Litopenaeus vannamei breeding farms in Brazil, and spread to Indonesia in 2006 (Senapin et al., 2007). This has caused severe economic losses to the shrimp breeding industry and has remained an active threat until this day. The diameter of the IMN virus is 40 nm, and it is a non-enveloped icosahedron, with double-strand RNA. The buoyant density of cesium chloride is 1.366 ng/ml, and its length is 7,560 bp (GenBank accession no. AY570892).

 

Host and Mode of Transmission of IMNV

 

It mainly infects Penaeus vannamei, but it is also established in Penaeus stylirostris and Penaeus monodon under artificial infection in experiments.

Infected organs and tissue: The virus is mainly present in striated muscle tissues such as muscle or (less commonly) myocardium, and other connective tissues, hemocytes and lymphoid organ parenchymal cells.

 

Mode of transmission

Horizontal infection

Through contaminated water sources and feeding on diseased shrimp, etc.

Vertical infection

Has not been proven by experiments

 

Signs and Symptoms of IMNV

 
  • Large areas of white necrosis in the muscles of the abdominal and telson somites
  • Body color becomes red
  • Coagulative or liquefactive necrosis of muscles and rhabdomyolysis
 

* The arrow marks the area with opaque muscles.

* Opaque muscles and myonecrosis in the abdominal somite (Alberto J.P. Nunes at al., 2010)

 

IMNV Prevention and Control Methods

   
  1. Feed Selection

     
    • Choose Grobest's functional feed to alleviate shrimps' stress.
    • Preventive usage of functional feed should be performed prior to signs of expected environmental stress to reduce the chance and magnitude of incidence of IMNV.
    • Add vitamins into the feed.
 
  1. Environmental & Water Quality Management

     
    • A certain degree of attention to the weather is required to handle weather changes accordingly.
    • Increase drainage capacity to prevent pond water quality from deteriorating.
    • Add probiotics to avoid hyperplasia of pathogens in water.
    • Avoid improper drug use, which may lead to hepatopancreatic damage
 
  1. Disease Control

     
    • Do not use biological feed that carries pathogens.
    • Dead shrimp should be removed as much as possible to avoid cross-infection.
    • Choose good shrimp seed that does not carry pathogens.
 
  1. Feed Shrimp with Grobest Functional Feed

     
    • Grobest functional feed strengthens intestinal immunity, protects the intestinal tract, and increases palatability and resistance to disease.
    • By stimulating the non-specific immune function of shrimp, it reduces the chance of viral disease infection; this has a significant effect in the prevention of shrimp disease.
    • Abundant vitamins and amino acids of our functional feed can supplement nutrients required for physiological needs, satisfy the need for enzymes and trace elements in the body, promote metabolism, and help to maintain healthy growth and development of shrimp.
    • Selected glucans in the Grobest functional feed can improve intestinal flora structure, promote metabolism, protect cells from free radicals' damage, maintain normal cellular metabolism, and enhance resistance.
    • By promoting the generation of digestive enzymes, it can enhance digestion efficiency. Moreover, it has antioxidative properties and can increase growth rate.
    • By increasing the animal's resistance to disease and cell resilience, it can also prevent stress-induced diseases.
 

Comparison of viral opaque muscles and other opaque muscles

 

IMNV

Opaque muscles

Pathogen

Virus

Multiple environmental & water quality factors

Condition

The muscles in particularly the fifth and sixth abdominal and the telson somites are distinctly opaque in infected shrimp.

The opaque muscles are not apparent when the shrimp is in water, and feed intake and swimming are relatively normal. The symptoms of opaque muscles are only obvious when the shrimp are taken out of the water. Diseased shrimp have opaque muscles in distributed areas or the entire abdominal somite.

Etiology

The virus causes coagulative necrosis of striated muscle.

Water temperature oscillation, bacterial factors, environmental and water quality, parasites