Page content: Victorian statutory requirement | Infectious agent | Identification | Incubation period | Public health significance & occurrence | Reservoir | Mode of transmission | Period of communicability | Susceptibility & resistance | Control measures | Outbreak measures | Additional sources of information

Victorian statutory requirement

Notification is not required.

School exclusion: exclude from school or children’s services centre if diarrhoea is present.

Infectious agent

The infective agents are Ascaris lumbricoides, a large intestinal roundworm (the female measuring up to 30 cm in length) and Ascaris suum, a similar parasite primarily affecting pigs and occasionally humans.

Identification

Clinical features
Many people have no symptoms and the first indication of ascariasis may be the passage of a worm by the anus, mouth or nostril. The usual life cycle of the worm is described below. Migration of the larval forms of the worm can cause symptoms due to various types of pneumonitis, liver damage or allergy.

Adult worms can cause a variety of abdominal symptoms and occasionally serious complications such as intestinal obstruction or biliary disease. Ascariasis aggravates malnutrition in underdeveloped countries.

Method of diagnosis
Diagnosis can be made by the identification of eggs or the presence of adult worms in faeces. Pulmonary involvement may be confirmed by identifying ascarid larvae in the sputum or gastric washings.

A. lumbricoides are often diagnosed on radiography either as worm shaped radiolucent areas in a barium filled intestine or in cholangiograms. Significant eosinophilia is noted in only about 10% of cases.

Incubation period

The lifecycle requires four to eight weeks to complete. Ascaris eggs are unsegmented when passed and require a period of two or three weeks outside the host to develop to the infective stage. Mature female worms have been estimated to produce an average of 200 000 eggs per day.

Public health significance & occurrence

Ascariasis infects an estimated one billion people around the world, more than any other parasitic infection.

Roundworm infections are common in temperate or tropical regions of the world including Australia. In communities where poor sanitary conditions exist often 100% of the population will harbour the parasite.

The prevalence and intensity of infection is usually highest in children aged three to eight years. Ascaris eggs are able to survive for months in faecal matter, sewage or even in a 10% formalin solution.

Reservoir

Ascaris eggs in soil or infected humans act as reservoirs.

Mode of transmission

Transmission occurs when eggs are swallowed from soil contaminated with human faeces or from uncooked produce contaminated with soil containing infective eggs. The eggs remain viable in moist soil for several months or years.

Transmission does not occur from direct person to person contact or from fresh faeces. The eggs hatch in the small intestine and larvae pass through the intestinal wall into the blood. They then pass to the liver and heart and to the lungs. In the lungs they have a further period of development. Larvae then penetrate through the alveoli into the airways and migrate up to the pharynx to be swallowed and reach their final destination in the small intestine. This occurs about 14–20 days after egg ingestion. Larvae then mature into adult worms which mate. Females begin to lay eggs 45–60 days after initial egg ingestion.

Period of communicability

Ascariasis is communicable as long as the mature fertilised female worm lives in the intestine. The usual life span is 12 months however it has been reported to be as long as 24 months.

Susceptibility & resistance

Infection does not infer immunity.

Control measures

Preventive measures
Promote effective hand washing, particularly prior to preparing or consuming food.

Control of case
The usual treatment is albendazole, pyrantel or mebendazole. In mixed infections with Ascaris and other parasites it is important to initially use a drug that is effective against Ascaris, thereby reducing the chances of stimulating the worm into untoward activity. Consult the current version of Therapeutic guidelines: antibiotic (Therapeutic Guidelines Limited).

When worms obstruct the pancreatic duct or migrate up the biliary tree, surgical or endoscopic removal of the worm may be necessary.

Students with ascariasis should be excluded from school or child care if diarrhoea is present.

Control of contacts
Consider faecal screening of household members to determine if they also require treatment. No school or child care exclusion is required for contacts.

Control of environment
Environmental sources of infection should be investigated.

Outbreak measures

Not applicable.

Additional sources of information

Markell, E, John, D, Krotoski, W 1999, Markell and Voge’s medical parasitology, 8th edn, ed. Saunders.