Infectious Hypodermal and Haematopoietic Necrosis Virus (IHHNV)

Clinical signs

• Runt Deformity Syndrome (RDS) — bent rostrum, deformed sixth abdominal segment, wrinkled antennae in vannamei
• Pronounced size variation in the same pond at 60–90 DOC — clear bimodal ABW distribution
• Reduced ADG of 10–30% versus species norm; harvest weight typically 8–14 g instead of 18–22 g
• Acute mortality only in P. monodon and P. stylirostris (up to 90%); vannamei rarely shows mortality
• Pale, bluish discolouration in heavily infected vannamei broodstock
• No reliable visual sign in early infection — diagnosis depends on PCR

Transmission

• Vertical — from infected broodstock to nauplii (the dominant route in modern outbreaks)
• Horizontal — cannibalism of infected shrimp; waterborne spread within ponds
• Mechanical — shared nets, buckets and workers between PL-positive and clean ponds
• Persistent — IHHNV integrates into shrimp genome; carriers shed virus for life
• No environmental temperature trigger — infection burden is set at stocking by PL quality

Diagnosis

• PCR on hepatopancreas, gill or pleopod tissue (gold standard) — single-step or nested
• Quantitative PCR for viral load grading — distinguishes low-grade carriage from clinical infection
• Field clue: bent rostrum + size divergence + normal mortality = PCR for IHHNV
• Histopathology: Cowdry type A intranuclear inclusion bodies in cuticular epithelium and connective tissue
• In-situ hybridization for definitive confirmation in research or insurance disputes

Treatment & emergency response

• No antiviral treatment exists — infection is lifelong once established
• Vannamei ponds usually carry to harvest; partial harvest at 80 DOC can recover larger animals while runts grow
• Monodon ponds with active mortality: emergency harvest if ABW >8 g and >50 DOC, otherwise drain and reset
• Reduce stocking density 20% in next cycle to lower cannibalism-driven horizontal spread
• Chlorinate pond water at 30 ppm for 24 h before discharging to prevent farm-wide contamination

Prevention

• Source PLs only from SPF (Specific Pathogen Free) hatcheries with current IHHNV-negative PCR certificates
• PCR-screen every PL batch on arrival — zero tolerance for IHHNV-positive batches
• Use IHHNV-tolerant vannamei lines where available (Kona, Shrimp Improvement Systems lineages)
• Disinfect intake water (chlorine 30 ppm, hold 24 h, dechlorinate)
• Avoid mixing PL batches from different hatcheries in the same pond
• Quarantine broodstock for 14 days with PCR confirmation before spawning
• Full pond dry-out + CaO 1,000 kg/ha + 14-day sun-drying between cycles

Biosecurity checklist

• Demand and file the IHHNV-negative PCR certificate for every PL batch
• Foot baths (200 ppm chlorine) at every pond entry, refreshed daily
• Dedicated nets, buckets and aerators per pond — colour-code to prevent cross-use
• No movement of workers from an IHHNV-positive pond to a clean pond on the same day
• Weekly ABW sampling per pond — track size variation as an early signal
• Quarantine pond for new broodstock (14-day minimum) with PCR clearance
• Log all PL sources and PCR certificates — required by EU and US importers on traceability audits

Frequently asked questions