Gastrointestinal parasitism in gulls (roundworms)
Gastrointestinal parasitism caused by roundworms (nematodes) is a common digestive condition in yellow-legged gulls (Larus michahellis), whether wild, in rehabilitation centers, or in captivity. Cylindrical worms called nematodes settle in...
What is it?
Gastrointestinal parasitism caused by roundworms (nematodes) is a common digestive condition in yellow-legged gulls (Larus michahellis), whether wild, in rehabilitation centers, or in captivity.
Cylindrical worms called nematodes settle in the bird's stomach or intestines.
They feed at the bird's expense and can cause irritation or even digestive obstruction when present in large numbers.
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:
Signs are often subtle at first.
Progressive weight loss may occur despite preserved appetite, or conversely appetite may decrease.
Digestive trouble such as diarrhea, regurgitation, or vomiting may appear.
The belly may seem bloated or distended.
The plumage becomes dull, less waterproof, and the bird appears tired and less active than normal.
In young birds, growth retardation is possible.
In severe infestations, roundworms may be visible in droppings or in regurgitated material.
Dehydration and general weakness may develop if the infestation is not treated.
When to consult without delay
This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.
Causes and risk factors
Infection is caused by gastrointestinal nematodes, particularly worms belonging to families common in seabirds and gulls.
The bird becomes infected by ingesting eggs or larvae present in the environment, contaminated water, or by consuming prey (fish, invertebrates) that harbor larval forms of the parasite.
The life cycle of some of these worms involves an intermediate host, such as a fish or crustacean, which explains the frequency of this parasitosis in a species with an opportunistic diet often associated with landfills, ports, and coastal areas.
Young gulls, immunologically immature, are more vulnerable.
Weakened, injured, or stressed birds, particularly those admitted to rehabilitation centers, often carry a higher parasite burden.
Frequenting areas heavily populated by gulls (landfills, ports, soiled beaches) promotes repeated exposure to parasites.
A diet based on waste or heavily parasitized prey also increases risk.
Close contact in colonies or in captivity facilitates transmission between individuals.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
The veterinarian takes into account the bird's history (origin, general condition, diet) and performs a thorough clinical examination. Diagnosis is confirmed by analysis of faeces (faecal examination) to look for parasite eggs. In some cases, digestive endoscopy or radiography may be helpful to assess the extent of infestation, particularly if intestinal obstruction is suspected.
Treatment
Treatment relies on antiparasitic drugs suitable for birds, prescribed and dosed only by a veterinarian. Additional support (rehydration, nutritional support) is often necessary for weakened birds. Post-treatment monitoring, with a new faecal check, confirms whether the treatment was successful.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
In the wild, there is no direct prevention that can be applied to a wild gull. In a rehabilitation centre or captive setting, enclosure hygiene, water and food quality, and regular parasite checks by a veterinarian help limit the risk of heavy infestation. Preventing access to stagnant, contaminated water and poor-quality prey also helps reduce exposure to parasites.
Possible complications
Heavy untreated infestation can lead to intestinal obstruction, digestive perforation, or severe malnutrition. In an already weakened bird (injury, young age, stress), parasitism can worsen its overall condition and compromise survival chances, particularly in a rehabilitation centre.
When to see a veterinarian
Visible weight loss or persistent loss of appetite
Repeated diarrhoea or vomiting
Worms visible in faeces or regurgitation
Swollen or distended abdomen
Marked lethargy, bird lying still
Poor growth in a young gull
Prognosis
The prognosis is generally good for light to moderate infestation treated with appropriate antiparasitic drugs. It becomes more guarded when infestation is heavy, long-standing, or combined with general weakness, particularly in young birds or those already fragile when admitted to a rehabilitation centre.
Frequently asked questions
Does the gull catch these worms by eating garbage?
Yes, opportunistic feeding by gulls, often linked to landfills and harbor areas, promotes the ingestion of parasites present in waste or in contaminated prey.
Can this parasitic disease be transmitted to humans?
These roundworms are specific to birds and do not present any known risk of transmission to humans under normal conditions.
Should a wild gull infested with parasites automatically be captured?
No, a light infestation is often well tolerated. Capture and treatment mainly concern birds that have already been taken in, are weakened, or showing clear clinical signs.
How is the presence of roundworms confirmed?
A veterinarian performs a fecal analysis to search for parasite eggs, which allows confirmation of the diagnosis before any treatment.
References
ESCCAP — European Scientific Counsel Companion Animal Parasites
WOAH — Organisation mondiale de la santé animale (ex-OIE)
Content reviewed by the TunisieVet editorial team · Updated 21 August 2026
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