Understanding Ascaris lumbricoiedes (Ascariasis)

Aetiological agent is Helminth, nematode: Ascaris lumbricoiedes.

The agent is a large nematode (roundworm) infecting the small intestine. Adult males measure 15-31cm*2-4mm, females 20-40cm*3-6mm. Eggs undergo embryonation in the soil; after 2-3 weeks they become infective and may remain viable for several months or even years in favourable soils.

The larvae emerge from the egg in the duodenum, penetrate the intestinal wall and reach heart and lungs via the blood. Larvae grow and develop in the lungs. Nine to ten days after infection they break out of the pulmonary capillaries into the alveoli and migrate through the bronchial tubes and tracheae of the pharynx where they are swallowed.

They reach the intestine 14-20 days after infection. In the intestine they develop into adults and begin laying eggs 40-60 days after ingestion of the embryonated eggs. The life cycle is complete after 8 weeks.

Incubation period: First appearance of eggs in stools 60-70 days following ingestion of the eggs. Symptoms of larval ascariasis appear occur 4-16 days after infection.

It is generally asymptomatic. Gastrointestinal discomfort, colic and vomiting; fever; observation of live worms in stools. Some patients may have pulmonary symptoms or neurological disorders during mitigation of the larvae (van-de-Venter, 2000).

Adult worms can live 12 months or more. The source/reservoir includes humans; soil and vegetation on which faecal matter containing eggs have been deposited.

Ingestion of infective eggs from soil contaminated with faeces or of contaminated vegetables and water.

Use of toilet facilities; safe excreta disposal; protection of food from dirt and soil; thorough washing of produce.

Food dropped on the floor should not be eaten without washing or cooking, particularly in endemic areas. Thermal processing, good hygiene practices during production and processing.

The occurrence is worldwide.