Gastrointestinal parasitism in opossums (roundworms)
Gastrointestinal roundworm parasitism is a very common condition in opossums (Didelphis virginiana), whether wild or brought into captivity for care. It is an infestation of the intestine by nematodes, microscopic to visible roundworms depe...
What is it?
Gastrointestinal roundworm parasitism is a very common condition in opossums (Didelphis virginiana), whether wild or brought into captivity for care. It is an infestation of the intestine by nematodes, microscopic to visible roundworms depending on their life stage.
These parasites live at the animal's expense, feeding partly on intestinal contents or blood, and can disrupt normal digestion. Most wild opossums carry a certain number of these parasites without becoming sick, but a heavy parasite burden, especially in young animals, weakened or stressed individuals, can cause actual clinical disease.
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 vary depending on the severity of infestation.
A lightly parasitized opossum may show no visible symptoms.
When the parasite burden is heavier, diarrhea may occur, sometimes with soft or mucoid stools, occasional vomiting, a belly that appears swollen or bloated, a dull coat in poor condition, progressive weight loss despite sometimes normal appetite, or conversely a loss of appetite.
Young opossums are more susceptible: they may show delayed growth, general weakness, and dehydration if diarrhea persists.
In the stool or sometimes in vomit, it is possible to see roundworms directly—thin and whitish, resembling small spaghetti.
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 intestinal nematodes, roundworms belonging notably to the families of ascarids and hookworms, which colonize the opossum's digestive tract.
Infestation most often occurs through ingestion of eggs present in the environment (soil, vegetation soiled by feces), through contact with parasitized prey or carrion, or sometimes through skin penetration by larvae of certain worm species.
Young opossums, particularly those separated from their mother very early or taken in as orphans, are the most vulnerable because their immune system is still immature.
Crowded conditions in captivity, an environment soiled by regularly uncleaned feces, significant stress (transport, change of surroundings), unbalanced diet, or underlying disease all favor excessive parasite multiplication.
Wild opossums living in areas heavily frequented by other animals or with high population density are also more at risk.
Transmission
Transmission occurs mainly through the fecal-oral route, via ingestion of worm eggs present in contaminated environment, or through contact with parasitized prey. Certain larvae can also penetrate directly through the skin.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
Diagnosis is based mainly on fecal parasite examination (fecal flotation) performed by the veterinarian, which identifies and quantifies worm eggs present.
In some cases, direct observation of worms in feces or vomit strongly suggests diagnosis, but laboratory confirmation is still recommended to tailor treatment.
Complete physical examination (hydration status, weight, coat condition, abdominal palpation) completes the assessment.
Treatment
Treatment relies on administration of antiparasitic drugs (deworming medications) suited to the type of worm identified, prescribed and dosed only by a veterinarian experienced in wildlife or exotic animals.
Supporting care may be added in case of dehydration or weakness: rehydration, nutritional support.
Parasite rechecking after treatment verifies treatment effectiveness.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Thorough maintenance of bedding and enclosure, with daily feces removal, greatly reduces the risk of reinfection, particularly in captivity or wildlife care facilities.
Regular veterinary checkups with fecal parasite examination allow detection of infestation before severe symptoms appear.
Good overall hygiene, appropriate diet, and stress reduction help maintain effective natural defenses against parasites.
Possible complications
Heavy untreated infestation can cause severe dehydration, significant weight loss, anemia in case of blood-feeding worms, and in young fragile animals, risk of death.
Intestinal obstruction, though rare, remains possible with extreme parasite burden.
When to see a veterinarian
Visible worms in feces or vomit
Persistent diarrhea or abnormal stools for several days
Visible weight loss or abnormally swollen abdomen
Lethargy, weakness, or refusal to eat
Any orphaned young opossum taken in, even without apparent symptoms
Prognosis
The prognosis is generally good when infestation is detected and treated before complications develop.
Young opossums that are weakened or heavily parasitized require more careful management, but they generally respond well to treatment combined with appropriate supportive care.
Frequently asked questions
Does a wild opossum necessarily have worms?
Most wild opossums carry a certain amount of intestinal worms without becoming ill. Problems arise mainly when the parasitic load becomes too heavy, particularly in young animals or weakened individuals.
Can you give an over-the-counter dewormer without veterinary advice?
No, it is not advisable to deworm an opossum without a prior diagnosis. The type of worm must be identified and the product chosen by a veterinarian, as some antiparasitics are unsuitable or dangerous for this species.
Can these worms be transmitted to humans or domestic animals?
The direct risk is generally low with good hygiene, but it is still preferable to wash your hands after any contact with an opossum or its droppings, and to prevent dogs and cats from being exposed to them.
How do you know if your rescued opossum is parasitized if it shows no visible symptoms?
Only a fecal parasitological examination performed by a veterinarian can detect mild infestation, even in the absence of visible signs.
References
CDC — Centers for Disease Control and Prevention
Content reviewed by the TunisieVet editorial team · Updated 26 August 2026
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