White Spot Disease in Red King Crab
White Spot Disease is a severe viral infection affecting many crustaceans, including the red king crab (Paralithodes camtschaticus). It is caused by WSSV (White Spot Syndrome Virus), which is highly contagious and can result in significant...
What is it?
White Spot Disease is a severe viral infection affecting many crustaceans, including the red king crab (Paralithodes camtschaticus). It is caused by WSSV (White Spot Syndrome Virus), which is highly contagious and can result in significant mortality in affected populations, both in captivity and in the wild. The disease's name comes from small white spots that may appear on the carapace of infected animals, although this sign is not always visible in red king crabs.
Key point
Reportable disease in many countries due to its significant economic and health impact on crustacean farming operations.
Commonly observed signs
These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.
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Signs are often subtle or nonspecific in red king crabs. Small white spots or marks may be visible on the inner surface of the carapace, along with slowed movement, loss of activity, refusal to eat, and affected animals becoming withdrawn. In severe cases, rapid and massive mortality can occur without any other visible signs.
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 WSSV, a DNA virus belonging to the family Nimaviridae. This virus infects cells in many tissues (gills, digestive tract, muscle, connective tissue) and multiplies rapidly, especially when the animal is weakened by stress or poor rearing conditions.
Poor water quality, sudden temperature or salinity fluctuations, high animal density, stress from transport or handling, and the presence of other crustaceans already carrying the virus promote the appearance and spread of the disease.
Transmission
The virus is transmitted through direct contact between animals, through contaminated water, by ingestion of infected carcasses or tissues (cannibalism), and potentially through contaminated equipment or vehicles. Some crustaceans can be healthy carriers of the virus without showing clinical signs and can contribute to its spread.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
Definitive diagnosis depends on specialized laboratory tests (molecular biology such as PCR, histology) performed by a veterinary laboratory or an official organization competent in aquatic pathology. Clinical observation alone cannot confirm the disease.
Treatment
There is no validated antiviral treatment for this disease. Management focuses mainly on limiting spread: isolation of suspected animals, improvement of farming conditions, and general supportive care of the animal under the supervision of a veterinarian or aquatic pathology specialist.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Prevention relies on strict biosecurity measures: health screening of introduced animals, quarantine, disinfection of equipment and tanks, careful management of water quality, and minimizing stress during handling. There is no vaccine for this disease.
Possible complications
The disease can cause rapid and severe mortality in a group of animals, resulting in major economic losses in farming. It may also permanently weaken wild populations if introduced into them.
When to see a veterinarian
Appearance of unusual white patches on the shell of one or more animals.
Sudden or unexplained mortality in a group of crabs.
Reduced activity, loss of appetite, or abnormal isolation in the animals.
Suspicion of recent introduction of unscreened animals into the same tank or farming area.
Prognosis
The prognosis is guarded to poor in the case of confirmed infection, particularly in high-density farming systems, due to the potential for high mortality and the absence of specific curative treatment. Early detection and rapid containment measures are essential to limit losses.
Frequently asked questions
Is white spot disease dangerous for humans?
No, this virus does not infect humans. It affects only crustaceans and is not considered a zoonosis.
Can a royal crab affected by white spot disease be treated?
There is no specific antiviral treatment. Management focuses mainly on isolating affected animals and improving their living conditions to limit spread.
How to know if your crab is infected?
Only specialized laboratory analysis can confirm the infection. Clinical signs alone, such as white spots, are not sufficient to make a definitive diagnosis.
Can this disease affect other crustaceans?
Yes, the virus responsible can infect many species of crustaceans, including shrimp and other crabs, which facilitates its spread between species.
References
WOAH — Organisation mondiale de la santé animale (ex-OIE)
Content reviewed by the TunisieVet editorial team · Updated 28 August 2026
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