parasitic disease Pig

Gastrointestinal parasitism in pigs (roundworms)

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Definition Signs Causes Transmission Diagnosis Treatment Prevention Complications When to see a vet Prognosis FAQ Sources Affected species

What is it?

Gastrointestinal parasitism in pigs encompasses infestations by roundworms (nematodes) that live in the pig's stomach or intestines. The most common is Ascaris suum, a large whitish worm that can measure several centimetres. Other roundworms such as Oesophagostomum, Trichuris suis, or Strongyloides ransomi may also be involved. These parasites are widespread in pig farms, particularly when hygiene is poor. Young pigs are especially affected, being more susceptible than adults.

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:

Diarrhea Weight loss Loss of appetite Dull coat Stunted growth Vomiting Cough Hard or painful abdomen Visible worms in stools Fatigue

In piglets, infestation often manifests as stunted growth and a dull coat. Appetite may decrease and the animal appears more tired than its littermates. Digestive disturbances sometimes develop: diarrhoea, loose faeces, or occasionally visible abdominal discomfort when the belly is touched. In heavy infestations from ascaris larvae migrating through the lungs, coughing may be observed. In some cases, adult worms may be visible directly in faeces or in vomit. Many infested pigs, especially adults, show no visible signs despite harbouring parasites.

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 nematodes (roundworms) that colonise the pig's digestive tract. Ascaris suum is the most common and most pathogenic in young pigs. Eggs of this parasite are shed in faeces and become infective after several weeks in the environment. Pigs become infected by ingesting these eggs present in soil, contaminated bedding, or contaminated water. After ingestion, larvae migrate through the liver and lungs before settling in the intestines as adult worms.

Young pigs, particularly weaned piglets and fattening pigs, are most at risk. Outdoor housing or dirt-floored facilities promote the accumulation of eggs in the environment. High stocking density, inadequate cleaning of facilities, and soiled bedding also increase risk. Stress, unbalanced feed, or other concurrent illnesses can worsen the effects of parasitism.

Transmission

Transmission occurs via the oral route, by ingesting parasite eggs present in an environment fouled by contaminated faeces. Ascaris eggs are particularly resistant and can survive for several months or even several years in soil depending on climatic conditions.

Diagnosis and care

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

The veterinarian relies on clinical signs and especially on faecal analysis at the laboratory (faecal floatation) to detect parasite eggs and identify the species involved. In some cases, post-mortem examination of an animal confirms the presence of adult worms in the intestine or lesions on the liver and lungs.

Treatment

Treatment is based on the use of antiparasitic medications (wormers) effective against nematodes, prescribed and dosed by the veterinarian. Choice of product and treatment frequency depend on the type of farm and level of infestation. Nutritional support may be offered to help weakened animals return to normal weight.

Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.

Prevention

Regular cleaning of housing and frequent manure removal limit the buildup of infective eggs. Floors that are easy to disinfect are preferable to dirt bedding. A regular antiparasitic programme tailored to the farm helps limit animal infestation. Avoiding overcrowding and following strict hygiene rules between pig groups also reduces contamination risk.

Possible complications

Heavy infestation with Ascaris larvae migrating through the liver can leave characteristic scars called "milk spots", visible at slaughter, which reduce carcass value. Significant lung involvement can favour secondary respiratory infections. In piglets, untreated parasitism can cause lasting growth delay and poorer feed conversion.

When to see a veterinarian

A piglet or pig shows unexplained growth delay.

Worms are visible in faeces or vomit.

Diarrhoea persists or is accompanied by general lethargy.

Cough appears in several animals from the same group with no obvious respiratory cause.

Several animals in the same farm show similar signs.

Prognosis

The outlook is generally favorable with appropriate antiparasitic treatment and improved housing hygiene. Heavily infested young animals may take longer to catch up on growth. Without treatment, infestation persists and can have lasting effects on herd performance.

Frequently asked questions

Is parasitism by roundworms in pigs dangerous for humans?

The risk to humans is very limited. Ascaris suum is closely related to human Ascaris, but cases of transmission to humans remain rare and anecdotal. Good hygiene after contact with animals or their environment is always recommended.

How to tell if your pigs are infested?

Many infested pigs show no visible signs. Only a fecal analysis performed by a veterinarian can confirm the presence of parasites and guide treatment.

Should all pigs in a farm be dewormed?

This depends on the context and risk level. The veterinarian can establish a deworming program tailored to the farm structure rather than treating indiscriminately.

Do Ascaris eggs survive for long in the environment?

Yes, these eggs are very resistant and can persist for several months or even several years in the soil, which makes cleaning the premises essential to limit reinfestation.