Gastrointestinal parasitism in the vaquita (roundworms)
The vaquita (Phocoena sinus) is the smallest cetacean in the world, a species of porpoise found only in the northern Gulf of California, Mexico. It is now on the brink of extinction, with only a handful of individuals recorded in the wild....
What is it?
The vaquita (Phocoena sinus) is the smallest cetacean in the world, a species of porpoise found only in the northern Gulf of California, Mexico. It is now on the brink of extinction, with only a handful of individuals recorded in the wild. Gastrointestinal parasitism caused by roundworms (nematodes) is one of the conditions described in porpoises and small cetaceans in general. It corresponds to the presence of worms lodged in the stomach or intestine, which disrupt digestion and can weaken the animal. In a species as rare as the vaquita, any disease, even mild in other animals, takes on particular importance because it adds to the already known threats such as accidental capture in fishing nets.
Key point
The vaquita is listed as critically endangered, with a wild population estimated at only a handful of individuals; any health compromise in an individual has exceptional significance for the species' survival.
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:
In cetaceans generally, an infestation by digestive roundworms may go unnoticed if it remains mild. In more pronounced cases, progressive weight loss, loss of appetite, fatigue, or behavior less active than normal may be observed. Digestive disturbances such as loose stools or vomiting are possible but difficult to detect in a wild marine animal. These signs are not specific and may also correspond to other diseases or simple stress.
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 condition is caused by the presence of roundworms (nematodes) in the stomach or intestine. In porpoises and dolphins, several families of marine nematodes are known as digestive parasites, generally transmitted through the food chain—that is, by ingestion of prey (fish, crustaceans) already carrying parasitic larvae.
The exclusively marine lifestyle and diet based on fish and cephalopods naturally expose cetaceans to this type of parasite, which circulates in the marine ecosystem. An animal that is weakened, young, old, or already stressed by other environmental factors could be more susceptible to heavy infestation. The vaquita's near-extinction status and the extreme rarity of direct observations make any precise assessment of the frequency or severity of this parasitism in the wild population very difficult.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
Diagnosis of gastrointestinal parasitism in a cetacean typically relies on examination of fecal matter or digestive contents for parasite eggs or larvae, or on post-mortem examination during necropsy. In the vaquita, such examination is possible only in exceptional circumstances, such as when studying an animal found dead and stranded, because routine capture and handling are not performed on this critically endangered species.
Treatment
In captive cetaceans or care facilities, broad-spectrum anthelmintic agents can be used under strict veterinary supervision. For wild vaquitas, no such treatment is applied in practice, as capture and individual medical monitoring are not feasible.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
There is no preventive measure applicable directly to wild vaquitas, as no routine veterinary intervention is possible with this free-ranging species. Preserving the quality of the Gulf of California marine ecosystem, limiting pollution, and maintaining a balanced food chain indirectly support the overall health of the species and its prey.
Possible complications
A heavy and prolonged infestation could theoretically contribute to general weakening of the animal, weight loss, and reduced resistance to other stressors (infections, stress, reproductive difficulties). In a species with only a handful of individuals remaining, any factor that weakens an individual carries weight for the population's overall survival.
When to see a veterinarian
This situation does not apply to the general public: the vaquita is a protected wild species not kept in captivity.
Any observation of a stranded, injured, or distressed individual should be reported immediately to the competent Mexican authorities and to scientific teams dedicated to conserving the species.
No intervention by non-specialists should be attempted.
Prognosis
The prognosis specifically relating to gastrointestinal parasitism is poorly understood in vaquitas because so few individuals exist and there is virtually no direct medical monitoring. In cetaceans generally, moderate infestation is often well tolerated, whereas heavy infestation or infestation combined with other diseases can worsen the animal's overall condition.
Frequently asked questions
Can a vaquita infested with worms be treated?
In practice, no: the vaquita lives exclusively in the wild and no routine capture is carried out. Individual treatment is only conceivable in the very exceptional context of an emergency rescue supervised by specialists.
Is parasitism a major cause of the vaquita's decline?
No. The main threat to the species is accidental capture in fishing nets (particularly those intended for another fish, the totoaba). Gastrointestinal parasitism is an individual health problem, not the primary cause of the species' impending extinction.
How do we know that the vaquita can have roundworms?
Knowledge comes mainly from the study of other porpoises and small cetaceans, as well as from rare post-mortem examinations conducted on vaquitas found dead.
Can this parasite be transmitted to humans?
There is no element indicating a risk of transmission to humans in this context, particularly since there is no direct contact with the wild species.
References
WOAH — Organisation mondiale de la santé animale (ex-OIE)
Content reviewed by the TunisieVet editorial team · Updated 03 September 2026
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