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Shrimp Hemocyte Iridescent Virus - Causes and Prevention Methods

Shrimp Hemocyte Iridescent virus (SHIV)

  • Family: Iridoviridae, new genus
  • DNA virus
  • Initially described in 2014, massive mortality (80%) of L. vannamei in China
  • Clinical signs:
    • empty stomach and guts,
    • pale hepatopancreas,
    • soft shell
    • White head
    • Black spots appeared at the connection of abdominal part and pleopod when shrimp dead.
    • The shell may be slightly red at the beginning of the disease.

Black Leg

SHIV

Cannot be washed

Sediment contamination

Washable

  • Histology: pyknosis and basophilic inclusions in haematopoietic tissue and haemocytes.
  • Susceptible species: P. vannamei, Fenneropenaeus chinensis and Macrobrachium rosenbergii.
Source of information: Emerging disease: Shrimp Hemocyte Iridescent Virus (SHIV) Clarification: Shrimp disease SHIV detected in China, Thailand, but not Vietnam... In 2019, the International Committee on Taxonomy of Viruses formally named this virus as decapod iridescent virus 1 (DIV1).

Route of Transmission

  • Horizontal transmission: asymptomatic shrimp, pond water, pathogen in water, infected shrimp…
  • Vertical transmission: No vertical transmission has been confirmed (detected in live bait).
  • Outbreak season: Mostly after November, when the water temperature is below 22℃.
  • Other outbreak conditions:
    1. When the differences in water temperature increase, infection rate also rises.
    2. In the final stage of farming, when it comes to 40~60 shrimps/kg, the sediment quality is poor, while the level of ammonia nitrogen and nitrite in the water is relatively high; such environment allows the virus to go active and therefore shrimps become susceptible to the disease.
  • No correlation between outbreak and salinity was found.
 

Hosts of SHIV and Control Methods

 

  • Species of susceptible hosts

  • Cross-species transmission has been confirmed in polyculture and close related species farming models.

Risks

  • Pathogen may spread to new species, which complicates pathogen ecology.
  • When it is transmitted to closely related species, the pathogen gains an even stronger pathogenic variation screening effect-- larger pathogenic diversity and greater possibility of higher virulence.

Prevent infection via cannibalism

  • Infected shrimps should be removed as many as possible, in order to avoid infecting other shrimps.

Other advices for farmers

  • During outbreaks, ban polyculture and intercropping of close species.
  • Do not breed multiple closely related species in the same farm, in adjacent farms or nearby farms.
  • Do not to breed multiple closely related species in the same hatchery.

Ponds disinfection

  • To further prevent the virus penetration, no more live organisms should be brought into the ponds.

Do not feed live bait

  • To prevent virus transmission and infection.

Discharge contamination

  • Outbreak is often accompanied by poor environmental management.
 

  • Use healthy PL without SHIV

  • Ensure abundant level of dissolved oxygen

  • Implement proper biosecurity to prevent cross-infection

  • Feeding Grobest functional feed

  • Strengthen immunity, apply preventive gut health management, enhance disease resistance, and support perfect palatability.
  • Stimulate non-specific immune function in the shrimp, thus reduce the possibility of viral infection.
  • Rich vitamins and amino acids that constitute fulfilling nutritional supplements to satisfy physiological needs.
  • Improve intestinal flora structure, promote metabolism, protect cells from free radical damage, maintain normal cellular metabolism, and enhance disease resistance.
  • Promote the production of digestive enzymes to enhance digestion capacity. Additionally, its antioxidant function helps improve growth efficiency.
  • Increase disease resistance of the animal while stronger cell resilience also helps prevent stress-induced diseases.


Grobest developed functional feeds to strengthen aquatic animals' digestive systems. Scientists have proved that the gut is a very important immune organ. A diversity immune cells are activated in the gut to enhance the immunity mechanism. Therefore, gut health management leads to better body immunity and lower risks of pathogen infection.

  • Before using Grobest functional feed, there are very few oil droplets at the tubules. ATM is visible, and the shape is sharp.
  • While using Grobest functional feed, there are more and more oil droplets at the tubules. ATM has been discharged, and the shape becomes oval.
  • After using Grobest functional feed, the tubules are full of oil droplets. No ATM is visible, and the shape becomes rounder.
  • ATM = Aggregated Transformed Microvilli.
  • Before using Grobest functional feed, there are blurry spots of inflammation in the gut.
  • While using Grobest functional feed, the spots gradually turn clear and inflammation improved.
  • After using Grobest functional feed, the spots are in clear clusters without inflammation.
 

The above performance data shared from customer 's successful case, but the actual result may impact by environment, seed, feeding management in verity changing factors.

 

Case study

While Grobest TS team conducted customer service in Guangdong area during the past six months, we found that Mr. Chen's farm had massive death shrimp with SHIV infection symptom, such as black pleopods, pale hepatopancreas. Grobest confirmed the farm had SHIV infection after we did biological diagnosis and PCR detection. In order to assist Mr. Chen keep away from having big losses like other farmers, hereafter the case had confirmed, Grobest technician gentle reminded Mr. Chen utilize Grobest functional feed (I-MAX series) to enhance shrimp immunity, as well as improve water quality by Grobest PSB and EM bacteria products simultaneously.
As the surrounding farmers had witnessed Mr. Chen's big success in limiting the losses caused by SHIV, many farmers have already decided to use Grobest functional feed to enhance the SHIV resistance for their shrimps in the latest stocking season.

Grobest gentle remind the usage of functional feed

  • Water quality indicators: Ammonia <0.3 ppm, Nitrite <1 ppm, D.O. 4 ppm and above and pH 7.5–8.5. When water becomes poor, use Grobest water treatment - PSB and EM bacteria to improve water quality, and use functional feed.
  • Method of use
    • Fry stage (< DOC30): Continuously apply for 15 days.
    • Usual prevention: Continuously apply for 5~7 days every two weeks.
    • Outbreak season: Continuously apply for 15 days when climate changes or before disease outbreak.
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