Helminth

Helminth

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Helminth, Parasitic Worm, Worms, Helminthiasis, Tapeworm, Cestode, Fluke, Trematode, Platyhelminth, Flatworm, Nematode, Roundworm

  • See Also
  1. Parasitic Infection
  • Definitions
  1. Helminth (Parasitic Worm)
    1. Parasitic invertebrates, divided into Flatworms (Tapeworms and Flukes) and Roundworms
  2. Platyhelminth (Flatworms)
    1. Bilaterally symmetrical Flatworms divided into Tapeworms (Cestodes) and Flukes (Trematodes)
  3. Nematode (Roundworm)
    1. Round-bodied, unsegmented, Parasitic Worms
  • Epidemiology
  1. Helminths are the most common infectious cause in the developing world
  2. In contrast, less common in returning travelers than other forms of infectious disease (Bacteria, virus or Parasite)
    1. Helminth infections are unusual if travel less than 1 month
    2. Infection may be associated with decreased Eosinophils
  • Pathophysiology
  1. Helminths generate no significant immune response while alive
    1. Immune response is typically robust to eggs and dead Helminths
  2. Helminths stimulate an immune response when they migrate out of the intestinal tract
    1. Extraintestinal migration to other human tissue results in Eosinophilia
  3. Organisms that remain in the intestinal tract (without migrating to other human tissue) do NOT cause Eosinophilia
    1. Trichuris trichiura (Whipworm)
    2. Enterobius vermicularis (Pinworm)
  • Causes
  • Flatworms (Platyhelminths)
  1. Tapeworms (Cestodes)
    1. Ingestion of Tapeworm larvae in undercooked or raw fish or meat
      1. Taenia solium (Pork Tapeworm, Cysticercosis)
      2. Taenia saginata (Beef Tapeworm)
      3. Diphyllobothrium latum (Freshwater Fish Tapeworm)
    2. Ingestion of fertilized Tapeworm eggs
      1. Echinococcosis (Hydatid Disease)
      2. Hymenolepis nana (Dwarf Tapeworm)
  2. Flukes (Trematodes)
    1. Exposed skin penetration
      1. Schistosomiasis
      2. Trichobilharzia schistosomes (Swimmer's Itch)
  • Causes
  • Roundworms (Nematodes)
  1. Intestinal Nematodes (worms mature in human intestinal tract)
    1. Ingestion of Nematode eggs
      1. Ascaris lumbricoides
      2. Trichuris trichiura (Whipworm)
        1. Remain in intestinal tract without Eosinophil response
      3. Enterobius vermicularis (Pinworm)
        1. Remain in intestinal tract without Eosinophil response
    2. Ingestion of encysted Nematode larvae (in pig Muscle)
      1. Trichinella spiralis (Trichinosis)
    3. Exposed Skin penetration by Nematode larvae
      1. Ancylostoma duodenale or Necator americanus (Hookworm)
      2. Strongyloides stercoralis
  2. Blood and tissue Nematodes
    1. Vector Borne
      1. Onchocerca Volvulus (river blindness)
        1. Via Black Fly bite (near rivers and streams in Africa, Central America and South America)
      2. Lymphatic Filariasis (Wuchereria bancrofti or Brugia malayi)
        1. Wuchereria bancrofti (via Mosquito Bite in pacific islands or Africa)
        2. Brugia malayi (via Mosquito Bite in southeast asia)
    2. Ingestion
      1. Dracunculus medinensis
        1. Via ingestion of Nematode larvae in contaminated fresh water (Africa, Middle East or India)
      2. Visceral Larva Migrans (Toxocariasis)
        1. Via egg ingestion of Toxocara canis from dogs or Toxocara cati from cats
    3. Skin Penetration
      1. Cutaneous Larva Migrans (Ancylostoma braziliense, Ancylostoma caninum)
        1. Via skin penetration by Tapeworm larvae from dog or cat feces
        2. Occurs in tropical and subtropical regions (Southeast Asia, Africa, South America, Caribbean)
        3. Occurs in southeastern U.S.
  • Causes
  • Presentations
  1. Soil Transmitted Helminths (STH)
    1. Worldwide the most common intestinal Parasites worldwide (2.6 billion infections/year)
    2. Ascaris lumbricoides (Roundworm)
    3. Ancylostoma duodenale or Necator americanus (Hookworm)
    4. Trichuris trichiura (Whipworm)
  2. Transmission from Dogs and Cats
    1. Visceral Larva Migrans
    2. Ocular Larva Migrans
    3. Cutaneous Larva Migrans
  3. Transmission by Ingestion
    1. Ingestion of larvae (e.g. undercooked or raw fish or meat, contaminated water)
      1. Taenia solium (Pork Tapeworm, Cysticercosis)
      2. Taenia saginata (Beef Tapeworm)
      3. Diphyllobothrium latum (Freshwater Fish Tapeworm)
      4. Trichinella spiralis (Trichinosis, pork)
      5. Dracunculus medinensis
    2. Ingestion of fertilized eggs
      1. Echinococcosis (Hydatid Disease)
      2. Hymenolepis nana (Dwarf Tapeworm)
      3. Ascaris lumbricoides
      4. Trichuris trichiura (Whipworm)
      5. Enterobius vermicularis (Pinworm)
      6. Visceral Larva Migrans (Toxocariasis)
  4. Exposed skin penetration
    1. Schistosomiasis
    2. Trichobilharzia schistosomes (Swimmer's Itch)
    3. Cutaneous Larva Migrans (Ancylostoma braziliense, Ancylostoma caninum)
    4. Ancylostoma duodenale or Necator americanus (Hookworm)
    5. Strongyloides stercoralis
  5. Vector-Borne Helminths
    1. Onchocerca Volvulus (river blindness, via Black Fly bite)
    2. Lymphatic Filariasis (Wuchereria bancrofti or Brugia malayi via Mosquito Bite)
  6. Nematode Larvae that migrate to the lungs (and are coughed, swallowed and mature in the intestinal tract)
    1. Ascaris lumbricoides
    2. Ancylostoma duodenale or Necator americanus (Hookworm)
    3. Strongyloides stercoralis
  • References
  1. Gladwin, Trattler and Mahan (2014) Clinical Microbiology, Medmaster, Fl, p. 362-81
  2. Alshami (2023) Helminthiasis, StatPearls, Treasure Island, Fl +PMID: 32809360 [PubMed]
  3. Hotez (2008) J Clin Invest 118(4):1311-21 +PMID: 18382743 [PubMed]