Medicine & USMLE

Ascaris lumbricoides (giant roundworm)

  1. Giardia lamblia
  2. Toxoplasma gondii
  3. Entamoeba histolytica
  4. Cryptosporidium
  5. Naegleria fowleri
  6. Trypanosoma brucei
  7. Plasmodium Overview
  8. Plasmodium Disease (Malaria)
  9. Babesia
  10. Trypanosoma cruzi
  11. Leishmania
  12. Trichomonas vaginalis
  13. Enterobius vermicularis (pinworm)
  14. Ascaris lumbricoides (giant roundworm)
  15. Strongyloides stercoralis (threadworm)
  16. Ancylostoma and Necator
  17. Trichinella spiralis
  18. Trichuris trichiura (whipworm)
  19. Toxocara canis
  20. Onchocerca volvulus
  21. Loa loa
  22. Wuchereria bancrofti
  23. Taenia solium
  24. Diphyllobothrium latum
  25. Echinococcus granulosus
  26. Schistosoma
  27. Clonorchis sinensis
  28. Sarcoptes scabiei (Scabies)
  29. Pediculus humanis and Phthirus pubis (Lice)


Ascaris lumbricoides, or simply Ascaris, is a parasite colloquially known as the giant roundworm. Ascaris is typically transmitted in a fecal-oral manner, classically through the ingestion of eggs from contaminated water or food. Infection with Ascaris results in a clinical syndrome known as Ascariasis, which manifests as early pneumonitis with a bloody cough, due to larvae migrating through the lungs. Later in the course of disease, the larvae are swallowed and return to the GI tract, where they mature into giant roundworms. The size of the roundworms is significant because these roundworms can cause GI obstruction, especially at the site of the ileocecal valve. A serious complication of this GI obstruction is intestinal perforation. Non-specific signs of a parasite infection includes eosinophilia, although more specific diagnosis can be achieved by way of a Stool O&P or PCR assessment for Ascaris DNA. Finally, the first-line treatment for Ascaris is the Bendazole drugs, such as Albendazole and Mebendazole. A second-line treatment prefered in some populations is Pyrantel Pamoate. 

Key Points

  • Ascaris lumbricoides
    • Characteristics
      • Also known as the giant roundworm
    • Transmission
      • Fecal-oral
        • Ingestion of eggs in contaminated food or water
    • Pathogenesis and Presentation: Ascariasis
      • Larvae penetrate intestinal wall and migrate through lungs
        • Early pneumonitis
          • Eosinophilia
      • Swallowed larvae mature in intestines and become large worms
        • GI obstruction
          • Large worms may obstruct the intestines or biliary tracts
            • May cause obstruction at ileocecal valve
    • Diagnosis
      • Fecal eggs seen in Stool O&P
      • Eosinophilia on laboratory studies
    • Treatment
      • Bendazoles
      • Pyrantel pamoate as second-line agent preferred in pregnant women