Gastrointestinal Parasitism in the Great White Shark (Roundworms)

What is it?

Gastrointestinal parasitism caused by roundworms (nematodes) is a condition frequently observed in the great white shark, both in the wild and, more rarely, in captive individuals kept for short periods of observation. These parasites live in the shark's stomach or intestines and feed at the animal's expense. In a healthy shark, a moderate parasite load is often well tolerated and considered part of the normal ecology of the species. Problems typically arise when the parasite load becomes heavy or when the animal is already weakened by other factors.

Commonly observed signs

These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.

Causes and risk factors

The condition is caused by the presence of nematodes (roundworms) that parasitize the digestive tract and belong to groups known to infest many shark and ray species. The life cycle of these worms typically involves one or more intermediate hosts, often fish or marine invertebrates that the shark consumes during feeding. The great white shark becomes infected mainly through feeding on prey already carrying parasitic larvae.

A diet rich in heavily parasitized prey increases the risk of infestation. Young sharks in a rapid growth phase may be more susceptible to the effects of high parasite loads than a robust adult. Weakened general health, injury, environmental stress, or immunosuppression promote clinical signs in response to a parasite load that would otherwise be well tolerated. The density of infested prey in a given hunting area can also influence the level of exposure.

Transmission

The shark becomes infected by consuming prey (fish, marine invertebrates) carrying nematode larvae, with these prey serving as intermediate hosts in the parasite's life cycle. There is no direct transmission between sharks.

Diagnosis and care

Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.

Treatment

In nature, no treatment is applied to a parasitized great white shark, as the species cannot be handled in this context. In the rare cases where an individual is cared for in a specialized facility, an antiparasitic suitable for cartilaginous fish may be considered by an experienced veterinary team, taking into account sharks' particular sensitivity to certain medications.

Prevention

Possible complications

A very high parasite load can contribute to progressive weight loss, decline in overall physical condition, and increased vulnerability of the animal to other diseases or environmental stressors. In an already weakened individual, parasitism can worsen a precarious health status and contribute to an overall decline in body condition.

When to see a veterinarian

Prognosis

In a great white shark with good overall health, a moderate roundworm burden is generally well tolerated and does not significantly affect the vital prognosis. In cases of heavy parasitic load or associated general weakness, the prognosis becomes more guarded, as parasitism can then contribute to progressive deterioration of the shark's health status.

Frequently asked questions

References

WOAH — Organisation mondiale de la santé animale (ex-OIE)

Content reviewed by the TunisieVet editorial team · Updated 29 August 2026