12. Which of the following statements about Ascaris lumbricoides is incorrect
a. Ascaris lumbricoides is one of the largest nematode
b. Ascaris lumbricoides can cause pneumonia
c. Both dogs and cats are intemediate host of Ascaris lunbricoides
d. A lumbricoides is transmitted by ingestion of eggs
Answers
Explanation:
Symptoms correlate with worm load:light loads are asymptomatic; heavier loads cause abdominal symptoms, diarrhea, and sometimes malnutrition. A bolus of worms may obstruct the intestine. Migrating larvae can cause pneumonitis and eosinophilia.
Structure
Ascaris lumbricoides is the largest intestinal nematode of humans. Females are up to 30 cm long; males are smaller. Three types of eggs may appear in feces: fertilized, unfertilized, and decorticated.
Multiplication and Life Cycle
Adults in the small intestine produce eggs that pass in feces, embryonate in soil, are ingested, and hatch. The larvae migrate from the intestine to the lung and back to the intestine, where they mature.
Pathogenesis
Migrating larvae cause eosinophilia and sometimes allergic reactions. Erratic adult worms may invade other organs. Heavy infections can impair nutrition.
Host Defenses
Resistance increases with age; the mechanism is not clear.
Epidemiology
Egg viability is supported by warm, moist soil. Transmission is favored by unsanitary disposal of feces. Prevalence is highest in children.
Diagnosis
Diagnosis is made most often by identifying eggs in stool; occasionally, erratic adults emerge from body orifices.
Control
Control is by sanitary disposal of feces and by education and treatment.
Hookworms
Clinical Manifestations
Itching may occur where larvae enter skin (“ground itch”). Pneumonitis, cough, dyspnea and hemoptysis may mark the migration of larvae through the lungs. Depending on the adult worm load, intestinal infection can cause anorexia, fever, diarrhea, weight loss, and anemia.
Structure
Two species of hookworms infect humans: Ancylostoma duodenale and Necator americanus. They are distinguished by the morphology of the mouth parts and male bursa. Females are larger. Eggs are oval, thin-shelled, and transparent. Eggs hatch to release rhabditiform larvae, which mature into filariform (infective stage) larvae.
Multiplication and Life Cycle
Adults attach to the mucosa of the small intestine. Eggs passed in feces embryonate and hatch in soil; mature larvae penetrate the skin and migrate first to the lungs, and then to the intestine, where they mature into the adult stage.
Pathogenesis
Larvae entering skin often cause an erythematous reaction. Larvae in the lung may cause small hemorrhages, eosinophilic infiltration, and pneumonitis. Blood loss from sites of intestinal attachment may cause iron-deficiency anemia.
Host Defenses
Spontaneous self-cure may represent a hypersensitivity reaction. Infection induces high levels of IgE.
Epidemiology
Transmission is favored by poor sanitation and warm moist soil. Prevalence rises with age.
Diagnosis
Diagnosis is by detection of eggs and (sometimes) larvae in stool. Low levels of hemoglobin are suggestive.
Control
Control is by sanitary disposal of feces and by education and treatment.