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An infection of the intestinal tract caused by the adult Ascaris lumbricoides and clinically manifested by vague symptoms of nausea, abdominal pain and cough. Live worms are passed in the stool or vomited. Occasionally, they may produce intestinal obstruction or may migrate into the peritoneal cavity (l)
Ascaris is cosmopolitan in distribution. It is the most common helminthic infestation. It is estimated that about 1.3 billion people were infected worldwide and the prevalence of the infestation was about 250 million during 1997.
Epidemiological Determinants
Agent Factors:
Agent: The causative agent is Ascaris lumbricoides. Males and females are different, with females being longer and thicker compared to males (Fig).The life cycle of infection is given in figure. The life span of an adult is between 6-12 months, maximum reported being 15 years.
Reservoir of Infection: Man is the only reservoir.
Infective Material: Faeces containing the fertilized eggs.
Host: Infection rates are high in children; they are the most important disseminators of infection. Adults seem to acquire some resistance. However, the infections are seen in adults also. There is a high degree of host-parasite tolerance. Roundworms rob man of his food. They contribute to malnutrition especially in children who may show growth retardation.
Environment: Ascaris is a "soil transmitted'· helminth. The eggs remain viable in the soil for months or years under favourable conditions. Important factors regulating population of eggs are-temperature, moisture, oxygen pressure and ultra-voilet radiation from the sunlight. A low temperature inhibits the development of eggs. Clay soils are most favourable for the development of ascaris eggs, in contrast to moist porous soils.
Human Habits: The human habit of open air defecation infects the soil. Soil pollution is usually concentrated around houses where small children who do not have regular habits pollute the house and surrounding areas. Infective eggs can then easily reach other children who play on the ground and contaminate their hands and food.
Period of Communicability: Until all fertile females are destroyed and stools are negative.
Mode of Transmission
- Faecal-Oral-Route: by ingestion of infective eggs with food or drink. Foods eaten raw such as salads and vegetables and polluted water readily transfer the infection. Other means of spread are fingers contaminated with soil or by ingestion of contaminated soil (pica). There is increasing evidence that dust may play an important role in the dissemination of ascaris in arid areas.
Incubation period: About 2 months.
Clinical Features:
- No symptoms
- Stage 1: worm larvae in the bowels attach to bowel walls
- Stage 2: worm larvae migrate into the lungs:
- Fever and breathing difficulty
- Coughing and pneumonia
- Stage 3: worm larvae enter the small intestine and mature into worms and remain there to feed
- Abdominal symptoms
- Abdominal discomfort
- Intestinal blockage - may be partial or complete
- Partial intestinal blockage
- Total intestinal blockage
- Severe abdominal pain
- Vomiting
- Restlessness
- Disturbed sleep
- Worm in stool and vomit
Prevention and Control
Primary Prevention
Primary prevention methods are effective in interrupting transmission. These are: sanitary disposal of human excreta to prevent or reduce faecal contamination of the soil, provision of safe drinking water, food hygiene habits, and health education of the community in the use of sanitary latrines, personal hygiene and changing behavioural patterns. Best strategy of prevention can be achieved by considering the life cycle of the parasite and ecological, social and cultural circumstances prevailing in a community. Vegetable should be thoroughly washed in a mild solution of Potasium permanganate and properly cooked before use. Finger nails should be regularly cut to avoid the collection of dirt and eggs below them. Hands should be properly washed with some antiseptic soap before touching edibles or eating.'
Secondary Prevention
Effective drugs are available for the treatment of the human reservoir.
Mass Treatment: Periodic deworming is essential specially in places of high prevalence of parasites and protein-energy malnutrition. It can be undertaken at intervals of 2 to 3 months. Mass treatment will not interrupt transmission of the disease, but merely reduces the worm load. Ascariasis is disappearing spontaneously in certain areas as a result of improved sanitation.
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