Ancylostoma duodenale and Necator americanus

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Summary of Ancylostoma duodenale and Necator americanus

Necator americanus is a species of hookworm that lives in the small intestine of hosts such as humans, dogs, and cats. Ancylostoma duodenale and Necator americanus are the two human hookworms that are discussed together as the cause of hookworm infection. These worms can cause anemia in affected patients by biting and sucking blood from the intestinal wall. Transmission occurs when larvae penetrate the skin, typically when patients walk barefoot on contaminated sand or soil. This may cause cutaneous larva migrans, characterized by a serpiginous, pruritic rash near the site of penetration. Treatment is with bendazoles, pyrantel pamoate, or ivermectin.

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Ancylostoma duodenale and Necator americanus

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Chapter 82 Nematodes (Roundworms) ANCYLOSTOMA DUODENALE & NECATOR AMERICANUS osms.it/ancylostoma-duodenale osms.it/necator-americanus PATHOLOGY & CAUSES ▪ Infectious hookworm species Adult morphology ▪ Ancylostoma duodenale ▫ Two ventral plates on buccal capsule’s anterior margin; two large teeth fused at base (male 8–11mm, female 10–13mm long) ▪ Necator americanus ▫ Two dorsal/ventral cutting plates around buccal capsule’s anterior margin, paired subdorsal/subventral teeth (male 7–9mm, female 9–11mm long) ▪ A. duodenale, Necator americanus: most common hookworm species causing helminth gastrointestinal infection ▫ Light infection (< 100 worms) ▫ Moderate infection (100–500 worms) ▫ Heavy infection (500–1000 worms) ▪ Pathophysiology ▫ Hookworm attachment, hyaluronidase release → intestinal wall degradation, capillary laceration → anticoagulant peptides, inhibits platelet function inhibitor production → bleeding facilitation → extravasated blood ingested (approx. 0.5mL daily) ▫ Moderate–heavy infections → chronic iron-deﬁciency anemia; protein malnutrition Infectious form ▪ Filariform larva Life cycle ▪ Infectious form maturation ▫ Female A. duodenale lays 10,000– 30,000 eggs daily ▫ Female N. americanus lays 5,000– 10,000 eggs daily ▫ Human feces egge release → soil deposition → eggs hatch (24–48 hours—favorable conditions) → rhabditiform larvae (L1) → transformation to infectious ﬁlariform larvae (L3) in 5–10 days ▪ Human stages ▫ Filariform larvae skin penetration → passage through veins to heart, lung → pulmonary alveoli penetration, ascend bronchi to pharynx → coughed up/swallowed into small intestine → maturation → intestinal wall attachment via buccal capsule ▪ Some A. duodenale larvae undergo developmental arrest in gut tissues/muscle ▫ Await more favorable environmental conditions (hypobiotic larvae) ▪ Natural life-span ▫ A. duodenale: approx. one year ▫ N. americanus: 3–5 years Transmission ▪ Contaminated soil contact → percutaneous larval penetration ▪ Oral route ▪ Transmammary route RISK FACTORS ▪ Inadequate clean-water access ▪ Poor sanitary conditions ▪ Walking barefoot (endemic areas) COMPLICATIONS ▪ Severe iron-deﬁciency anemia; protein malnutrition → impaired growth, cognitive OSMOSIS.ORG 437

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Ancylostoma duodenale and Necator americanus

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A 35-year-old man comes to his general practitioner for examination of an erythematous rash on his foot that appeared three days prior. He says that the rash began about a week after taking a day trip to the beach, and complains that the rash is extremely itchy. His medical history is noncontributory. The rash is shown below. Which of the following is the most likely causal organism?

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