Helminths

• Parasitic worms


  • Cestodes
  • Trematodes
  • Nematodes

  
• Helminth


  Parasitic worm

  
• Helminths


  • Multicellular, eukaryotic organisms
  • Two major divisions: round worms (nematodes) and flatworms (platyhelminthes)
  • Flatworms further divided into tapeworms (cestodes) and flukes (trematodes)

  
• Helminths are macroscopic, but the diagnostic signs of infestation such as their eggs or larvae are microscopic

  
• Helminth life cycle


  • Egg
  • Larva
  • Adult worm

  
• Helminths usually require intermediate hosts during their larval stage

  
• Dioecious


  Male and female sex organs are in separate worms
• Monoecious


  Each worm has both sex organs
• Helminth infections of humans

  • Onchocerciasis
  • Trichinosis
  • Dracunculiasis
  • Paragonimiasis
  • Filariasis
  • Schistosomiasis
  • Cysticercosis
  • Hydatid cyst disease

  
• Helminth infections of the GI tract

  • Cestodes: Beef tapeworm, Dwarf tapeworm, Fish tapeworm, Pork tapeworm, Rat tapeworm, Dog tapeworm
  • Nematodes: Ascariasis, Hookworm, Pinworm, Whipworm, Strongyloidiasis
  • Trematodes: Fasciolopsiasis, Fascioliasis, Clonorchiasis

  
• Nematodes


  • Known as roundworms
  • Dioecious
  • Possess digestive, reproductive, excretory and nervous systems
  • Life cycle has 3 morphologic forms: ova, larvae and adult worms, except Trichinella spiralis which has no egg stage

  
• Types of nematodes


  • Intestinal nematodes
  • Blood-tissue nematodes
  • Intestinal-tissue nematodes
• Ascaris lumbricoides


  • Known as roundworm
  • Soil-transmitted helminth
  • Most common intestinal nematode of man

  
• Ascaris lumbricoides life cycle

  1. Eggs passed with feces

  2. Larvae develop in eggs

  3. Ingested eggs hatch, larvae invade intestinal mucosa, travel to lungs

  4. Larvae mature in lungs, ascend bronchial tree, swallowed

  5. In small intestine, larvae mature into adult worms

  6. Adult worms can live 1 to 2 years

  
• Pathology of ascariasis


  • Reaction of tissues to invading larvae
  • Irritation of intestine by mechanical and toxic action of adult worm
  • Complications from parasite's extraintestinal migration

  
• Clinical presentation of ascariasis

  • Vague abdominal pain
  • Eosinophilia during larval migration
  • Lactose intolerance and vitamin A malabsorption in moderate infections
  • Bowel obstruction, intussusception, volvulus, bowel infarction and intestinal perforation in heavy infections

  
• The WASHED framework for comprehensive control of soil-transmitted helminth infections
• Trichuris trichiura


  • Known as whipworm
  • Soil-transmitted

  
• Trichuris trichiura life cycle

  1. Unembryonated eggs passed in stool

  2. Eggs develop in soil

  3. Embryonated eggs ingested

  4. Larvae hatch, mature into adults in colon

  5. Females shed 3,000-20,000 eggs per day

  6. Eggs become infective in 15-30 days

  7. Adult lifespan is about 1 year

  
• Pathology of trichuriasis


  • Petechial hemorrhages from worms embedded in mucosa
  • Intestinal bleeding
  • Appendicitis or granuloma from worms in appendix

  
• Clinical presentation of trichuriasis

  • Infections over 5,000 eggs per gram of feces are usually symptomatic
  • Heavy infections can cause Trichuris dysentery syndrome and anemia
  • Also results in poor appetite, wasting, stunting, reduced intellectual and cognitive development in children

  
• Treatment and prevention of trichuriasis

  • Anthelminthic medications: albendazole and mebendazole
  • Avoid ingesting soil contaminated with human feces
  • Wash hands before handling food
  • Wash, peel or cook raw vegetables and fruits

  
• Hookworms


  • Necator americanus and Ancylostoma duodenale
  • Soil-transmitted, blood-sucking nematodes that attach to small intestine mucosa

  
• Hookworm life cycle


  1. Eggs passed in stool

  2. Larvae hatch and grow in soil

  3. Infective filariform larvae can survive 3-4 weeks in soil

  
• Hookworms


  • Blood-sucking nematodes that attach to the mucosa of the small intestines

  
• Hookworm life cycle


  1. Eggs passed in stool

  2. Larvae hatch and become infective filariform larvae

  3. Filariform larvae penetrate skin, travel to heart and lungs, then to small intestine

  4. Adult worms reside in small intestine

  
• Hookworm effects


  • Anemia and protein deficiency caused by blood loss
  • Can retard growth and mental development in children

  
• Hookworm diagnosis


  Identifying hookworm eggs in stool sample using microscope

  
• Hookworm treatment


  Anthelminthic medications: albendazole and mebendazole
• Hookworm prevention


  • Not walking barefoot in areas with hookworm
  • Avoiding skin contact and ingestion of contaminated soil
  • Effective sewage disposal systems

  
• Pinworms


  • Small, thin, white roundworm called Enterobius vermicularis

  
• Pinworm life cycle


  1. Adult female deposits eggs on perianal fold

  2. Infection via self-inoculation or exposure to eggs

  3. Larvae hatch in small intestine, adults establish in colon

  4. Gravid females migrate nocturnally to oviposit on perianal skin

  
• Pinworm symptoms


  • Itchy anal region
  • Secondary bacterial infection
  • Teeth grinding, insomnia, abdominal pain

  
• Pinworm diagnosis


  Look for worms, tape test, examine under fingernails

  
• Pinworm treatment


  Antihelminthics: mebendazole, pyrantel pamoate, albendazole
• Pinworm prevention


  Handwashing, avoiding co-bathing, good hygiene practices, cutting fingernails
• Trematodes (flukes)


  • Possess primitive digestive tract
  • Two types: tissue-dwelling and blood-dwelling

  
• Tissue-dwelling flukes


  • Clonorchis sinensis, Fasciola hepatica, Paragonimus westermani, Fasciolopsis buski

  
• Blood-dwelling flukes


  • Schistosoma japonicum, Schistosoma haematobium

  
• Clonorchis sinensis


  Liver fluke parasite transmitted by eating raw/undercooked fish