Ascaris lumbricoides Suan Lui Teoh Danh Voong Introduction

Ascaris lumbricoides Suan Lui Teoh Danh Voong

Introduction n n a common cream colored roundworm that is parasitic in the intestines of humans Most common helminthic human infection Largest nematode to infect the human intestine An estimated 1 billion people are infected (1 out of 4 people in the world)

Geography n n Worldwide High prevalence in underdeveloped countries that have poor sanitation (parts of Asia, South America and Africa) Occurs during rainy months, tropical and subtropical countries Even occurs in rural areas in the United States

Host n Definitive host : Humans or pigs n Intermediate Host : -none-

Modes of transmission n n Occurs mainly via ingestion of water or food (raw vegetables or fruit in particular) contaminated with A. lumbricoides eggs. Occasionally inhalation of contaminated dust Children playing in contaminated soil may acquire the parasite from their hands Enhanced by the fact that individuals can be asymptomatically infected and continues to shed eggs for years Prior infection does not confer protective immunity

Morphology Fertile egg n mammillated n thick external layer n unembryonated n measures 55 -75 mm by 35 -50 mm

Morphology Cont. Infertile egg n elongated and larger than fertile egg n thin shelled n shell ranges from irregular mammillations to a relatively smooth layer completely lacking mammillations n measures between 85 -95 mm by 43 -47 mm

Morphology Cont. n Infertile n Fertile

Egg Can survive for prolonged periods as long as warm, shade, moist conditions are available and can live up to 10 years Eggs are resistant to unusual methods of chemical water purification Eggs are removed by filtration and killed by boiling. Developing larvae are destroyed by sunlight and desiccation

Morphology Cont. Adult worm: n n tapered ends; length 15 to 35 cm Female are larger in size and have a genital girdle

The 3 prominent “lips”

Life Cycle

Life Cycle Cont. 1. 2. 3. 4. 5. 6. 7. Females lay eggs in small intestine and eggs are passed out through feces. After 14 days, L 1 larvae develops in eggs L 2 larvae develops after one week Ingestion of raw foods, fruits or vege contaminated with eggs will cause infection Eggs hatch in small intestine, releases L 2 rhabditiform larvae L 2 penetrate intestinal wall, enter portal blood stream, migrate to liver, heart and lungs in 1 -7 days Moults twice to become L 4 larvae

Cont. 8. 9. 10. 11. Borrow out of blood vessels and enter bronchiols Migrate through the lungs into the trachea Enter throat and swallowed to end up in the small intestine Mature and mate, where they complete their life cycle

Food Habits n n Feeds on semi-digested contents in the gut Evidence show that they can bite the intestinal mucus membrane and feed on blood and tissue fluids

Symptoms associated with larvae migration n Migration of larvae in lungs may cause hemorrhagic/ eosinophilic pneumonia, cough (Loeffler's Syndrome) Breathing difficulties and fever Complications caused by parasite proteins that are highly allergenic - asthmatic attacks, pulmonary infiltration and urticaria (hives)

Symptoms Cont. Symptoms associated with adult parasite in the intestine n Usually asymptomatic n Abdominal discomfort, nausea in mild cases n Malnutrition in host especially children in severe cases n Sometimes fatality may occur when mass of worm blocks the intestine

HOST IMMUNE RESPONSE Innate Immune Response n Macrophage, neutrophils and most importantly eosinophils n The worms would be coated with Ig. G or Ig. E which would increase the release of eosinophil granules on the worm’s surface Adaptive Immune Response n General consensus is a Th 2 immune response with high IL-4 production, high levels of Ig. E, eosinophilia and mastocytosis

Diagnosis n Stool microscopy : eggs may be seen on direct examination of feces. n Eosinophilia: eosinophilia can be found, particularly during larval migration through the lungs n n n Imaging: In heavily infested individuals, particularly children, large collections of worms may be detectable on plain film of the abdomen. Ultrasound: ultrasound exams can help to diagnose hepatobiliary or pancreatic ascariasis. Single worms, bundles of worms, or pseudotumor-like appearance, individual body segments of worms may be seen. Endoscopic Retrograde Cholangiopancreatography (ERCP) : A duodenoscope with a snare to extract the worm out of the patient

Treatment n n n Mebendazole Albendazole Pyrantel pamoate Ivermectin Piperazine citrate Levamisole

Prevention n n Prevention of reinfection poses a substantial problem since this parasite is abundant in soil – therefore good sanitation is needed to prevent fecal contamination of soil Limit using human feces as fertilizer Treatment can be done on contaminated soil although it is not highly advised Mass treatments of children with single doses of mebendazole or albendazole – helps reduce transmission in community but can cause reinfection