Introduction 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 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
Modes of transmission 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
MorphologyFertile egg mammillated thick external layer unembryonated measures 55-75 mm by 35-50 mm
Morphology Cont.Infertile egg elongated and larger than fertile egg thin shelled shell ranges from irregular mammillations to a relatively smooth layer completely lacking mammillations measures between 85-95 mm by 43-47 mm
Morphology Cont. Infertile Fertile
EggCan survive for prolonged periods as long aswarm, shade, moist conditions are available andcan live up to 10 yearsEggs are resistant to unusual methods of chemicalwater purificationEggs are removed by filtration and killed by boiling.Developing larvae are destroyed by sunlight anddesiccation
Morphology Cont.Adult worm: tapered ends; length 15 to 35 cm Female are larger in size and have a genital girdle
The 3 prominent “lips”
Life Cycle Cont.1. Females lay eggs in small intestine and eggs are passed out through feces.2. After 14 days, L1 larvae develops in eggs3. L2 larvae develops after one week4. Ingestion of raw foods, fruits or vege contaminated with eggs will cause infection5. Eggs hatch in small intestine, releases L2 rhabditiform larvae6. L2 penetrate intestinal wall, enter portal blood stream, migrate to liver, heart and lungs in 1-7 days7. Moults twice to become L4 larvae
Cont.8. Borrow out of blood vessels and enter bronchiols9. Migrate through the lungs into the trachea10. Enter throat and swallowed to end up in the small intestine11. Mature and mate, where they complete their life cycle
Food Habits 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
SymptomsSymptoms associated with larvae migration Migration of larvae in lungs may cause hemorrhagic/ eosinophilic pneumonia, cough (Loefflers 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 Usually asymptomatic Abdominal discomfort, nausea in mild cases Malnutrition in host especially children in severe cases Sometimes fatality may occur when mass of worm blocks the intestine
HOST IMMUNE RESPONSEInnate Immune Response Macrophage, neutrophils and most importantly eosinophils The worms would be coated with IgG or IgE which would increase the release of eosinophil granules on the worm’s surfaceAdaptive Immune Response General consensus is a Th2 immune response with high IL-4 production, high levels of IgE, eosinophilia and mastocytosis
Diagnosis Stool microscopy :eggs may be seen on direct examination of feces. Eosinophilia : eosinophilia can be found, particularly during larval migration through the lungs 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
Prevention 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
Some cool pictures
How many people in the world are estimated to be infected with A. lumbricoides ?
Who are the definitive host/s of this parasite?
Name 2 modes of transmission?
What morphological difference canbe seen in fertile and infertile eggs?
Name the symptom caused by larvae migration in the lungs.