Ascaris suum


Causal agent

Ascaris suum – the large round worm of pigs

The adult worm is large the female is 20-40 cm long and the male slightly shorter at 15-20 cm.

The adult female may lay 2 million eggs per day.

An adult can live 6 months

Life cycle
















Egg+L3 stage ingested and swallowed

L3 hatch from egg in intestines

L3 penetrate intestine wall and migrate to liver

L3 migrate from liver to lung

L3 leave lung, coughed up and swallowed

L3 develop to L3 in intestines

Young adult develop

Eggs are passed

L1 develop in 10 days

L2/3 develop in 13-18 days

Prepatent period 40-52 days

Age group

Affects all age groups of pigs

Clinical signs


No clinical signs.  May be some reduction in growth rates due to competition between pig and worm for food.

Acute pneumonia

Ascaris, during the lung phase, may result in an asthmatic cough and the pig may have problems breathing.  Ascaris will exacerbate other pneumonic conditions, especially swine influenza.



In young pigs severe infestation may results in intestinal blockage, rupture and death



The eggs are very infective.  They are extremely resistant and can survive for more than 7 years in the environment.  Generally disinfectants have little effect on the eggs.  However, steam cleaning and direct sunlight will kill the eggs.



The eggs are extremely sticky and will be easily transported onto the farm by pigs, insects, birds and equipment

Note workers boots are a significant source


Post-mortem Lesions


“White spot” on the liver develop within days of infestation. 

However, they heal within 25 days


Small lesions may be seen in the lung, easier on histology


The presence of the adult worms may be seen in the intestine lumen

ascaris liver au 1

Ascaris gut 2

“White spot” in the liver – severe case

Heavy worm infestation in the intestine – seen at slaughter



White spot on liver in the slaughterhouse or at post-mortem


Presence of adult worms post anthelmintic treatment


Worm eggs seen during faecal examination using flotation technique.  Note Ascaris eggs require ZnSO4 flotation; normal salt solution will not work.  In addition, they may still be difficult to find.

Ascaris suum egg B

Ascaris worm from sow behind Ascaris kim 1

Egg in flotation

Adult worms seen after worming the pig



Many anthelmintics work against Ascaris larvae and adults


The problem with treatment is the rapid re-infestation and lesions heal within 25 days.  Withdrawal times may preclude use prior to slaughter


The adult worm in the gut does reduce the development of future larval migration

Common differentials


Stephanurus dentatus (kidney worm) in the early stages may result in a “milk spot” liver.  Later stages liver damage much more severe



No zoonotic implications. The human Ascaris lumbricoides worm is a separate species