White Spot Disease in Shrimp
White Spot Disease is a highly contagious viral infection of farmed and wild shrimp and other crustaceans (crabs, crayfish) that is often fatal. It takes its name from the small circular white spots that sometimes appear on the inside of th...
What is it?
White Spot Disease is a highly contagious viral infection of farmed and wild shrimp and other crustaceans (crabs, crayfish) that is often fatal. It takes its name from the small circular white spots that sometimes appear on the inside of the shell, particularly on the cephalothorax. It is one of the most feared diseases in shrimp farming worldwide because it can wipe out an entire pond in a few days and cause major economic losses. It is present in many shrimp-producing regions, including the Mediterranean basin and the Middle East.
Key point
Notifiable disease in many countries due to its major economic impact; capable of causing near-total mortality in a farm within days.
Commonly observed signs
These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.
Related signs — each one links to its page:
Infected shrimp become sluggish, stop feeding, and sometimes move toward the surface or sides of the pond. The shell may show small round white spots, most visible on the inside of the cephalothorax (front part of the body), but this sign is not always present or visible to the naked eye. The body may take on an unusual reddish or pinkish tint. Mortality increases very rapidly in the pond, sometimes within just a few days, affecting a large proportion of the stock.
When to consult without delay
This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.
Causes and risk factors
The disease is caused by White Spot Syndrome Virus (WSSV), a DNA virus belonging to the Nimaviridae family. It is one of the most devastating pathogens for shrimp farms worldwide. The virus infects many shrimp tissues: epidermis, gills, digestive tract, and lymphoid organ. It replicates rapidly and causes a systemic infection that often results in death within a few days.
Risk factors that promote the onset or worsening of the disease include stress (sudden changes in temperature or salinity, poor water quality), high stocking density, introduction of contaminated shrimp or water, presence of wild crustaceans carrying the virus around ponds, and seasonal transition periods when water temperatures fluctuate sharply. Early life stages (post-larvae, juveniles) appear particularly vulnerable to severe forms.
Transmission
The virus spreads very easily in several ways: through direct contact between shrimp (including cannibalism of dead or sick animals), through contaminated water, through vectors such as crabs, aquatic insects, or birds that carry viral particles between ponds, and through contaminated farming equipment. Transmission can also occur from a breeding female to her spawn (vertical transmission). The virus survives for some time in water and sediments, which complicates disinfection of affected ponds.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
There is no reliable at-home rapid test to confirm white spot disease.
Treatment
There is no specific and effective antiviral treatment against this disease. Farm management consists mainly of supportive measures and crisis management: improvement of water quality, stress reduction, removal and safe disposal of dead or dying animals to limit spread, and sometimes complete pond drain-down and disinfection if an outbreak is confirmed. Probiotics or immunostimulants may be used for general support under specialist guidance, but they do not cure the infection.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Prevention relies above all on farm biosecurity. Certified virus-free post-larvae must be used, incoming water quality must be monitored (filtration, disinfection), introduction of wild virus-carrying animals (crabs, aquatic insects) into ponds must be avoided, and equipment must be disinfected between rearing cycles. Stocking density must be controlled because overcrowding promotes transmission. Sudden changes in temperature or salinity, which stress shrimp, should be avoided because they encourage clinical disease expression in carrier animals. Regular health monitoring with PCR testing on shrimp batches allows early detection of contamination before the appearance of mass clinical signs.
Possible complications
Without intervention, mortality in an infected pond can reach nearly all animals within days to two weeks. The disease also weakens surviving shrimp, making them more susceptible to secondary opportunistic infections (bacteria, other viruses). Economically, a white spot outbreak can ruin a farm in a single season and cause lasting environmental contamination (sediments, water, wild carrier hosts such as crabs and other crustaceans).
When to see a veterinarian
Sudden and significant mortality of shrimp in a pond or aquarium.
Appearance of white spots on the shell of several animals.
Generalized abnormal behavior: lethargy, loss of appetite, animals moving to the surface.
Suspicion of contamination following introduction of new animals or water from an uncertain source.
Prognosis
The prognosis is very poor once infection is established: mortality in affected ponds is generally very high, potentially approaching 100% within a few days to two weeks. There is no individual recovery. The only hope for the operation is to limit spread to other ponds and restart with disease-free animals after complete site decontamination.
Frequently asked questions
Can white spot disease contaminate humans?
No. This virus is specific to crustaceans and poses no risk to human health. Infected shrimp are not dangerous to eat from a human health standpoint, even though they are unsuitable for sale due to quality and animal health regulation reasons.
Do all white spots on the shell mean this disease?
No, some spots can have other causes (mineral, bacterial). Only laboratory analysis can confirm the presence of the virus responsible for white spot disease.
Can you treat a sick shrimp?
There is no effective curative treatment against this virus. Management is limited to basin management measures and culling of infected animals to limit spread.
How does the virus get into a farm?
It can be introduced by infected larvae or breeding stock, by contaminated water, by birds or insects carrying infected debris, or by contaminated breeding equipment.
References
WOAH — Organisation mondiale de la santé animale (ex-OIE)
FAO — Organisation des Nations unies pour l'alimentation et l'agriculture
Content reviewed by the TunisieVet editorial team · Updated 29 August 2026
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