Ascaris suum, the large roundworm of pigs, is a parasitic organism found in swine populations globally. It is one of the most prevalent and economically impactful endoparasites in the swine industry, causing significant production losses. Adult worms, which are thick and whitish, reside in the pig’s small intestine. The parasite’s impact makes its control a subject of attention in veterinary science.
The Parasite Life Cycle
The life cycle of Ascaris suum begins when a pig ingests infective eggs from contaminated soil, feed, or water. These microscopic eggs are remarkably resilient and can survive in the environment for years, withstanding various chemical agents and temperature fluctuations. A single female worm can produce from 200,000 to over a million eggs daily, which are then passed into the environment through the pig’s feces.
Once ingested, the eggs hatch in the pig’s intestine, releasing larvae. These larvae then begin a complex migratory journey. They penetrate the intestinal wall, enter the portal blood vessels, and travel first to the liver. They are then carried by the bloodstream to the lungs, a journey that takes about nine to ten days.
Upon reaching the lungs, the larvae break through capillary walls into the air sacs. From there, they are coughed up into the throat and subsequently swallowed. This returns them to the small intestine, where they mature into adult worms over several weeks. The entire cycle, from egg ingestion to new egg production, takes approximately six to seven weeks.
Effects on Swine Health
The impact of an Ascaris suum infection on a pig’s health varies with the parasite’s life cycle stage. During the larval migration through the lungs, young pigs can develop respiratory symptoms. This may manifest as coughing, rapid shallow breathing, or a condition called “thumps.” These pulmonary issues can be worsened if the pig has co-infections with viruses or bacteria.
The presence of adult worms in the intestine leads to different problems. These parasites compete with the host for nutrients, which can result in poor feed conversion, reduced weight gain, and an unthrifty appearance. In cases of heavy infestation, the large worms can cause a physical blockage of the intestine or bile duct, leading to severe colic, vomiting, and potentially death if the intestine ruptures.
A significant economic consequence of this parasite is liver damage. The migration of larvae through the liver tissue causes inflammation and scarring, resulting in white, fibrous lesions known as “milk spots.” These spots are a primary reason for liver condemnation during postmortem inspections at slaughterhouses, representing a direct financial loss for producers.
Human Infection Risks
While pigs are the natural host for Ascaris suum, humans can become accidental hosts. Infection occurs when people ingest infective eggs, through contact with contaminated soil or by consuming raw vegetables grown in soil fertilized with raw pig manure. Infection cannot be acquired by eating pork products, as the eggs are not present in muscle tissue. Individuals who raise pigs or have frequent contact with their manure are at a higher risk.
When humans are infected, the parasite’s life cycle can mirror the one in pigs, including the migration of larvae through the lungs. This can cause respiratory symptoms like coughing, wheezing, and fever. In the intestinal phase, a light infection might cause no symptoms, but heavier worm burdens can lead to abdominal pain, nausea, and diarrhea.
There is considerable scientific discussion about the genetic relationship between A. suum and the human roundworm, Ascaris lumbricoides. Some researchers suggest they may be the same species. Regardless of their classification, the capacity of the pig roundworm to cause disease in humans is a recognized public health issue.
Prevention and Management in Pigs
Effective control of Ascaris suum requires a dual approach combining chemical treatment with environmental management. The use of anthelmintic drugs, or dewormers, is a common strategy. Deworming programs are implemented for the entire herd, including sows, gilts before farrowing, and growing pigs, to reduce the parasite load and limit egg shedding.
Treating the animals alone is often insufficient due to the persistence of the parasite’s eggs in the environment. Therefore, strict sanitation is a necessary part of any control program. This involves the regular removal of feces from pens and pastures to prevent the buildup of infective eggs. Farrowing crates and pens should be meticulously cleaned and disinfected between uses.
Managing pastures can also reduce exposure. Rotating pastures and avoiding the use of land for grazing that has recently been occupied by pigs can help break the cycle of reinfection. Since the eggs are highly resistant, washing hands after handling pigs or cleaning their pens can also help prevent the spread of the parasite to other animals and human handlers.