Intestinal Nematodes (Ingested) - The Oral Route
- General Features: Round, unsegmented worms with a complete digestive tract.
- Transmission: Acquired by ingestion of eggs or larvae.
- 📌 Mnemonic: Get sick if you EATTT these! (Enterobius, Ascaris, Trichinella, Trichuris).
| Organism | Transmission | Key Clinical Finding(s) |
|---|---|---|
| Enterobius vermicularis (Pinworm) | Fecal-oral (eggs) | Perianal pruritus, especially at night. Diagnosed by tape test. |
| Ascaris lumbricoides (Giant roundworm) | Fecal-oral (eggs) | Loeffler's syndrome (eosinophilic pneumonitis). Intestinal obstruction. |
| Trichuris trichiura (Whipworm) | Fecal-oral (eggs) | Often asymptomatic. Heavy infection can lead to rectal prolapse. |
| Trichinella spiralis | Undercooked meat (larvae) | Myalgias, periorbital edema, eosinophilia. |
⭐ Ascaris lumbricoides, the largest intestinal nematode, can cause intestinal obstruction and its larval migration phase can cause Loeffler's syndrome (eosinophilic pneumonitis).
Intestinal Nematodes (Cutaneous) - Skin Invaders
Nematodes that enter the body by penetrating the skin, often the feet. They migrate to the lungs, are coughed up, swallowed, and then mature in the small intestine.
| Organism | Transmission | Key Clinical Findings |
|---|---|---|
| Strongyloides stercoralis | Filariform larvae penetrate skin | Autoinfection cycle; hyperinfection in immunocompromised; eosinophilia. |
| Ancylostoma duodenale | Filariform larvae penetrate skin | Microcytic anemia (more severe blood loss); ground itch. |
| Necator americanus | Filariform larvae penetrate skin | Microcytic anemia (less severe); ground itch. |
⭐ Hyperinfection Syndrome: In Strongyloides, corticosteroid use can trigger a fatal autoinfective cycle, leading to disseminated larval invasion of multiple organs and septic shock from gut bacteria translocation.
Tissue & Filarial Nematodes - Blood & Body Dwellers
These nematodes inhabit blood and subcutaneous tissues, transmitted by insects.
| Organism | Vector | Clinical Features |
|---|---|---|
| Wuchereria bancrofti | Mosquito | Elephantiasis, lymphatic filariasis, lymphedema |
| Brugia malayi | Mosquito | Similar to Wuchereria, causes elephantiasis |
| Onchocerca volvulus | Female blackfly | River blindness, hyperpigmented skin, nodules |
| Loa loa | Deer fly, horse fly | African eye worm, transient Calabar swellings |
| Dracunculus medinensis | Copepod | Guinea worm disease, skin ulcer, worm emerges |
- Diagnosis: Blood smear (Giemsa stain) to find microfilariae (timing matters: Loa loa during day, Wuchereria at night).
- Treatment: Diethylcarbamazine (DEC) for most, but Ivermectin for Onchocerciasis.
⭐ River Blindness: Onchocerca volvulus microfilariae in the eye cause irreversible blindness. Treatment with Ivermectin is key, but it does not kill adult worms.
Nematode Pharmacology - The Worm Killers
| Drug | Mechanism (brief) | Key Indications (Nematodes) |
|---|---|---|
| Bendazoles (Albendazole) | Inhibits parasitic microtubule polymerization. | Broad-spectrum: Ascaris, Hookworm, Pinworm, Whipworm. |
| Pyrantel Pamoate | Depolarizing neuromuscular blocker → spastic paralysis. | Pinworm (Enterobius), Roundworm (Ascaris). |
| Ivermectin | Activates glutamate-gated Cl- channels → flaccid paralysis. | Strongyloides, Onchocerca volvulus (River Blindness). |
| Diethylcarbamazine (DEC) | Sensitizes microfilariae to phagocytosis. | Loa loa, Wuchereria bancrofti (Elephantiasis). |
High‑Yield Points - ⚡ Biggest Takeaways
- Enterobius vermicularis (pinworm) is diagnosed via the Scotch tape test and causes intense perianal itching.
- Ascaris lumbricoides, the giant roundworm, can cause intestinal obstruction and Loeffler's syndrome.
- Trichinella spiralis is contracted from undercooked pork and leads to myalgias and periorbital edema.
- Strongyloides stercoralis is unique for its autoinfection capability, dangerous in the immunocompromised.
- Hookworms (Ancylostoma, Necator) cause iron deficiency anemia by feeding on blood.
- Onchocerca volvulus, transmitted by the blackfly, results in river blindness.
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