Most common viral diseases affecting shrimp in aquaculture systems

   Viral diseases are very important in global shrimp aquaculture. The most serious viral diseases affecting shrimp include white spot syndrome virus (WSSV) highly lethal causing up to 100% mortality within 2-7 days, Yellow Head Virus (YHV) causing up to 100% mortality within 3-5 days and Taura syndrome Virus (TSV) causes significant economic impact on shrimp production.

The diseases spread through contaminated water, direct contact and movement of infected shrimp so effective biosecurity measures and management practices are crucial to mitigate viral diseases impact on shrimp production.  Disinfection of the surface of the eggs by iodophor treatment, a hatchery practice used to reduce the transmission of viral pathogens associated with egg, coelomic fluid or milt (A 10-30 min bath in 50-100 mg/L iodine solution as standard procedure performed both on recently fertilizes eggs during the water hardening step (Wood, 1979). Moreover, stocking of tilapia with shrimp in the pond culture can lower Infectious myonecrosis virus. As low-density tilapia into the pond can reduce cannibalism, consumes organic waste, control vectors as small crustacean, improve water quality and change water bacterial community.

Disease management strategies include:

·  Specific pathogen free (SPF) shrimp post-larvae stocks: use SPF broodstock and post-larvae to reduce disease

·  Vaccinations:  explore vaccination to enhance shrimp immune response.

· Using RNA interference technology, it works by introducing double strand RNA (dsRNA) that trigger the suppression of virus replication and has potential to boost the shrimp innate immune response. Despite its promise, challenges like cost-effective dsRNA production and efficient delivery methods for large-scale farms still need to be overcome.

·   Immunostimulation: Use immunostimulants to enhance innate immunity and provide viral resistance.

·  Early viral detection: use PCR diagnostics for early detection and rapid response.

·  Integrated disease management: combine biosecurity, management practices and treatment strategies.

· Regulating water quality parameters: monitoring water quality parameters such as oxygen, salinity, ammonia, and temperature.

·   Selection of the resistant strains of shrimp.

Biosecurity measures include:

·   Quarantine: quarantine for new shrimp before introducing to production system

·  Sanitation: disinfected equipment, vehicles and personnel.

·   Pathogen screening: regularly screen for pathogens using PCR or other diagnostic tools.

·  Access control: restrict access to production areas.

 Prevention and control

1. Developing domesticated SPF stocks, free of prevalent pathogens, as critical for predictable production stability. Significant efforts in breeding programs have already yielded stocks of *Penaeus vannamei* that demonstrate tolerance to TSV and IHHNV, despite lacking clarity on the underlying tolerance mechanisms, highlighting the need for persistent research in shrimp immunology.

2. The efficacy of shrimp vaccinations, traditional vaccination methods based on adaptive immunity are noted as inapplicable to invertebrates, leading to proposals for “immune priming” or “trained immunity.” Despite initial successes in protecting shrimp using killed pathogens and other immune response activators, no commercial products are presently available.

3. Additional research avenues include harnessing AMPs produced by shrimp in response to infections, which could provide targeted responses against specific pathogens.

4.  Emerging techniques involve using heterologous proteins—either viral or host-derived—to impede virus attachment to shrimp cells. However, practical delivery methods for these proteins remain a barrier to commercialization.

5. Using dsRNA has shown promise in combating viral infections and could pave the way for large-scale implementation, pending reductions in production costs and advancements in delivery methods.