Question

What is the mode of infection (route of entry into the human host) of Necator americanus (New World hookworm)?

• A. Skin penetration by filariform larvae
• B. Ingestion of embryonated eggs
• C. Bite of an infected female sandfly
• D. Ingestion of undercooked pork containing cysts

Hint:

Think barefoot in soil: hookworm filariform larvae bore through skin.

Answer 1

The Correct Option is A

Step 1: Identify the parasite. Necator americanus is one of the two common human hookworms (the other being Ancylostoma duodenale). Both belong to the nematodes (roundworms) and are major causes of iron-deficiency anaemia in the tropics.

Step 2: Recall the life cycle and infective stage. Hookworm eggs passed in faeces hatch in warm, moist soil to release rhabditiform larvae, which mature into the infective filariform (L3) larvae. These filariform larvae actively penetrate intact skin (classically the web of the toes/feet of barefoot individuals).

Step 3: Trace the migration. After skin penetration, the larvae enter venules, travel to the lungs, ascend the bronchial tree, are swallowed, and mature into adults in the small intestine where they attach and feed on blood. For Necator, skin penetration is the exclusive route (unlike Ancylostoma, which can also infect by oral ingestion of larvae).

Step 4: Why the other options are wrong. Ingestion of embryonated eggs is the route for Ascaris, Trichuris and Enterobius, not hookworm. The sandfly bite transmits Leishmania. Undercooked pork with cysts causes Taenia solium/Trichinella infection. None of these apply to Necator.

Key fact: Necator americanus infects man almost exclusively by filariform larvae penetrating the skin.