Lesson 3 NEMATHELMINTHES

• Nemathelminthes


  Unsegmented, bilaterally symmetrical worms with elongated, cylindrical bodies
• Digestive system of Nemathelminthes

  1. Stomodeum: mouth, esophagus, and buccal cavity

  2. Intestines

  3. Anus: called proctodeum
• Nervous system of Nemathelminthes

  • Two nerves that run along the length of the body on both the dorsal (back) and ventral (front) sides
  • Nerves connected to a nerve center found at the head
• Sensory organs of Nemathelminthes

  • Sensory organ usually located in the anterior end of the head region
  • In some, amphids found in the posterior head region
  • Some have a pair of caudal chemoreceptors called phasmus
• Excretory system of Nemathelminthes

  • Equipped with excretory canals along each side of the body for the elimination of waste materials
• Soil requirement for Nemathelminthes
• Ascaris Lumbricoides


  Also known as "Giant roundworm" or "Large Intestinal Roundworm"
• Ascaris Lumbricoides


  • Adult worm is creamy-white in color with an outer covering of cuticle
  • Appears in the Small Intestine
• Transmission of Ascaris Lumbricoides

  1. Ingestion of eggs from fecally contaminated soil or food

  2. Larvae released from eggs, penetrate intestinal wall, enter blood to liver, then lungs

  3. Larvae gain entrance into air sacs and migrate into bronchioles

  4. Larvae coughed up and swallowed, mature into adult worms in small intestines

  5. Eggs eliminated with feces, capable of surviving in soil, sewage, or water for several years
• Symptoms of Ascariasis


  • Asymptomatic infection with low worm burden
  • Adult parasite passed out with feces
  • Allergic reactions and pneumonia during larval migration
  • Abdominal pain, vomiting, fever, and abdominal distention from multiple adult worms
  • Intestinal obstruction from entangled worms
  • Worms can travel to different organs like appendix, liver, and bile ducts
  • Intestinal perforation and peritonitis
  • Secondary bacterial infections
• Enterobius Vermicularis


  Also known as "Pinworm" or "Seatworm"
• Enterobius Vermicularis


  • Found in cecum, appendix, and ascending colon
  • Lays up to 15,000 eggs at night
  • Egg is oval and flat on one side
  • Adult worm is small and yellowish-white in color with a clear, pointed tail
• Pinworm infection occurs worldwide, especially in temperate regions
• People at risk for pinworm infection


  • Children
  • Their caretakers
  • Institutionalized persons
  • Those in unsanitary and crowded living conditions
• Transmission of Enterobius Vermicularis

  1. Ingestion of eggs

  2. Self-contamination or autoinfection
• Symptoms of Enterobiasis


  • Asymptomatic infection
  • Intense itching with inflammation in the anal or vaginal area, especially at night
  • Intestinal irritation and mild nausea
  • Sleep deprivation and irritability
• Trichuris Trichiura


  Also known as "Whipworm"
• Trichuris Trichiura is found in the Large Intestine
• Children are at highest risk for Trichuris Trichiura infection when they play in contaminated soil
• Trichuris Trichiura


  • Adult worms burrow their hair-like anterior ends into the intestinal mucosa but do not cause significant anemia
• Transmission of Trichuris Trichiura

  Ingestion of eggs from fecally contaminated soil
• Symptoms of Trichuriasis


  • Ulcerative colitis
  • Chronic dysentery, severe anemia, or growth retardation
  • Rectal prolapse and hyperperistalsis in children
  • Abdominal pain, weakness, and dysentery in adults
• Ancylostoma Duodenale


  Also known as "Old World Hookworm"
• Necator Americanus


  Also known as "New World Hookworm"
• Transmission of Hookworms


  Larvae in soil penetrate skin
• Symptoms of Hookworm Infection

  • Pruritic papule or vesicle at site of skin penetration ("ground itch")
  • Pneumonia with eosinophilia during lung phase
  • Nausea, vomiting, and diarrhea from adult worms in intestines
  • Microcytic, hypochromic anemia from blood loss
  • Secondary bacterial infections
• Wearing shoes or protective footwear is important for prevention of hookworm infection, especially in endemic areas
• Strongyloides Stercoralis


  Also known as "Threadworm"
• Strongyloides Stercoralis is found in the Small Intestine
• Strongyloides Stercoralis infection is more common in tropical, sub-tropical, and warm, temperate areas, especially in agricultural areas
• Transmission of Strongyloides Stercoralis

  1. Larvae in soil penetrate skin

  2. Rare autoinfection
• Symptoms of Strongyloidiasis


  • Asymptomatic light infection
  • Skin irritation at site of entry
  • Pneumonitis from larval migration
  • Diarrhea and abdominal pain from numerous adult worms
  • Recurrent allergic reactions
• Wearing shoes or any protective footwear


  • Important, especially in endemic areas
• Strongyloides Stercoralis


  • Found in the Small Intestine
  • Threadworm infection occurs worldwide but is more common in tropical, sub-tropical, and warm, temperate areas
  • The parasite is frequently seen in agricultural areas where there is constant contact with soil
• Mode of transmission


  1. Larvae in soil penetrate skin

  2. Autoinfection (rare)
• Strongyloidiasis


  Also known as "Cochin China Diarrhea"
• Patients with light infection are usually asymptomatic
• Skin irritation at the site of entry is seen
• Migration of the larvae into the lungs lead to pneumonitis just like that of hookworm and Ascaris infections
• The presence of numerous adult worms in the intestines lead to diarrhea and abdominal pain