Swine Roundworm, Pig Ascarid
Rev 10/25/2025
Subclass: Chromadoria
Order: Rhabditida
Superfamily: Ascaridoidea
Family: Ascarididae
Note: The human ascarid, Ascaris lumbricoides, is morphologically indistinguishable from A. suum, the swine ascarid, and can mature in swine, while A. suum can mature in humans. Even so, the two ascarids are considered distinct species (Cruthers et al., 2020)
Males:
Females:
Ref: Roberts and Janovy, 2009; Wikipedia; Cruthers et al., 2020
Reported median body size for this species (Length mm; width micrometers; weight micrograms) - Click:
Occurs worlwide with infections most common in tropical and subtropical regions.
Infection of swine by Ascaris suum is known as ascariasis.
Reduction in growth rate of hosts
Rejection of liver contaminated with signs of infection (milk spots)
Swine (but can mature in humans)
Intestinal roundworm; inhabit the small intestine of swine
Life cycle is direct, no intermediate host required
Female worms are very large, lay up to 200,000 eggs/day in the host intestine; eggs pass out in the feces of pigs.
In the soil, eggs develop in about 4 weeks to the L1, L2, and finally the infective L3 that is ensheathed in the cuticle of the L2. Eggs are highly resistant to weather conditions and can remain infective for 4-10 years.
Eggs may be ingested by paratenic hosts, such as earthworms and beetles, in which they develop to the infective L3.
Swine become infected by ingesting the embryonated eggs directly or by ingesting a paratenic host.
The infective L3 is released from the egg in the stomach and small intestine and penetrates the wall of the cecum and colon. It migrates to the liver via the mesenteric and portal blood vessels.
Burrowing of L3 in the liver causes mechanical damage with subsequent hypersensitivity and allergic inflammation which results in whitish, fibrotic lesions (milk spots). The liver lesions have important economic impact as they result in condemnation of the organ by meat inspectors at slaughter.
The L3 leave the liver by traveling to the pulmonary capillaries and breaking out into alveoli in about 7 days.
The L3 in the respiratory tract are coughed up and swallowed to reach the small intestine where they molt to the L4 about 14 days post infection. The L4 molt to the L5 and become mature adults.
The prepatent period is 6-8 weeks (Cruthers et al., 2020.
Ecophysiological Parameters:
Contact with soil contaminated with eggs or larvae of nematode parasites is a common form of transmission that results in swine ansd even human infection. The nematodes can live for years as adults in the intestinal tract. Soil becomes contaminated by fecal material of infected hosts.
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Bethony, J., Brooker, S., Albonico, M., Geiger, S.M., Loukas, A., Diemert, D., Hotez, P.J. 2006. Soil-transmitted helminth infections: ascariasis, trichuriasis, and hookworm. The Lancet 9521:1521-1532.
Centers for Disease Control (CDC) 2018. Parasites - Ascariasis. (14 February 2018). Retrieved from www.cdc.gov/parasites/ascariasis/biology.html
Cruthers, L.R., Reinemeyer, C.R., Yazwinski, T.A., Marchiondo, A.A. 2020. Nematoda, Ascaridida. Chapter 2 in Marchiondo, Cruthers and Fourie (eds) Parasiticide Screening Vol 2. Academic Press
Lasker, A. 2008. eMedicine: Ascaris suum
Murray, P.R.; Rosenthal, K.S.; Pfaller, M.A.2005 Medical Microbiology, Fifth Edition. United States: Elsevier Mosby,
Read, A. F.; Sharping, A. 1995. The evolution of tissue migration by parasitic nematode larvae. Parasitology. 111:359-371
Roberts, L.S.; Janovy, J. Jr. 2009. Foundations of Parasitology, Eighth Edition. United States: McGraw-Hill.
Wikipedia, accessed Septmber, 2025
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