Introduction : Ascaris lumbricoidus causes ascariasis which is clinically manifested by symptoms of nausea, abdominal pain and cough. Liver worms are passed in stool or vomitus. Occassionally, they may produce intestinal obstruction or may migrate into peritoneal cavity.
EPIDEMIOLOGICAL FEATURES
Agent : Ascaris lumbricoidus lives in lumen of small intestine sexes are separate. The female measures 30-35 cm in length and male 12-30 cm.
Life cycle : Eggs are excreted in faeces. They become embryonated in external environment condition and become infective in 2-3 weeks. On ingestion by man, embryonated egg hatch in small intestine. The resulting larva penetrate the gut wall and are carried to liver and thus lungs via blood stream. In lungs, they molt twice. They break through the alveolar wall and migrate into bronchioles. They are coughed up through the trachea and then swallowed by human host. On reaching the intestine, they mature into adult in 60-80 days. The life span of an adult is between 6-12 months, maximum upto 1-5 years.
Reservoir of infection : man
Infective material : Faeces containing fertilized egg.
Host : Children are important host than adult as roundworm cause malnutrition in them with growth retardation.
Environment : Ascaris is a soil transmitted helminth. Important regulating factors are temperature, moisture oxygen pressure and UV radiation.
Human habit : Seeding of soil by ascaris egg takes place by open air defaecation. Infective egg can then easily reach younger children who play on ground and contaminate their hand and food.
PERIOD OF COMMUNICABILITY
Until all fertile females are destroyed and stools are negative.
MODE OF TRANSMISSION
Faeco-oral route i.e. by ingestion of infective egg with food or drink. Raw food like salad and vegetable readily convey infestation and so is polluted water. Also by fungus contaminated with soil on ingestion, playing in soil.
INCUBATION PERIOD
About 2 months.
