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Tufts OpenCourseware
Author: Amelia Virostko

1. Intestinal Helminths Not Capable of Systemic Spread

  1. Ascaris lumbricoides
    1. Humans are definitive host
    2. Found in soil
    3. Associated with lower SES
    4. Fecal-oral transmission
    5. Larvae hatch in small intestine and travel to liver via lymphatics, where they enter circulation
    6. Causes pneumonitis and eosinophilic pneumonia
    7. Can lead to malnutrition, intestinal obstruction, biliary obstruction, or pancreatitis
  2. Toxicara canis
    1. Dog is definitive host, human is intermediate host
    2. Fecal-oral transmission
    3. Penetrate intestinal wall and travel to other organs through bloodstream
    4. Visceral larva migrans
      1. hepatomegaly, wheezing, urticaria and prominent eosinophilia
      2. often from pica or puppies
    5. Ocular larva migrans
      1. arvae migrate to retina causing destructive inflammatory response
      2. can result in endophthalmitis
  3. Enterobius vermicularis (Pinworm)
    1. Humans are definitive host
    2. Found in temperate and tropical climates
    3. Often transmitted at summer camp
    4. Fecal-oral transmission
    5. Causes pruritis ani
    6. Can lead to intestinal mechanical obstruction or appendicitis
    7. Diagnose by presence of eggs on scotch tape test
  4. Trichuris trichiura (Trichuriasis)
    1. Human is the definitive host
    2. Transmission associated with poor sanitation and familial clustering
    3. Ingest eggs and larvae released in stomach
    4. Mature in cecum, where they have a lifespan of several years
    5. Most infections are asymptomatic, but can cause bloody diarrhea, tenesums, rectal prolapse, growth retardation, and anemia
  5. Ancylostoma duodenale, Necator americanus, A. braziliense (Hookworm)
    1. Found in rural areas of tropics and subtropics
    2. Associated with poverty and use of human excrement in fertilizer
    3. Filariform larvae penetrate skin (usually feet) and travel to lung, where they are swallowed
    4. Can persist in GI tract for years
    5. Ground itch from repeated exposure to worms
    6. Cutaneous larva migrans: serpiginous migration of worms in skin
    7. Can cause eosinophilic pneumonia
    8. Can cause anemia by damaging capillaries

2. Intestinal Helminths Capable of Systemic Spread

  1. Strongyloides stercoralis
    1. Found in tropics, subtropics, rural areas, institutional settings, lower socioeconimic conditions
    2. Filariform larvae penetrate skin of host, travel to lungs, and are swallowed into GI tract
    3. Free-living rhabditiform larvae lay eggs and can pass into stool where they auto-infect
    4. Auto-infection can lead to chronic infection causing GI symptoms
    5. Disseminated strongyloidiasis (hyperinfection) due to glucocorticoid effects on host
      1. potentially life-threatening
      2. colitis, ileus, polymicrobial sepsis, pulmonary hemorrhage, meningitis, purpura, larva currens
  2. Taenia solium (pork) and T. saginatum (cattle)
    1. Humans are definitive host, while cattle and pigs are intermediate hosts
    2. Infection from ingesting tissue cysts from undercooked meat 3
    3. Scolex attach to intestinal wall and mature into adult form
    4. Can live in host for up to 25 years
    5. Causes abdominal pain, and rarely mechanical obstruction
    6. Cysticercosis
      1. oncospheres of T. solium can become cysticerci and invade subarachnoid space producing arachnoiditis
      2. often leads to seizures, and can result in obstructive hydrocephalus

3. Helminths Causing Systemic Infection

  1. Trichinella spiralis (Trichinellosis)
    1. Acquired by eating undercooked meat
    2. Ingest cysts, which undergo excystation in stomach
    3. Larvae travel to small intestine and produce new larvae after mating
    4. Incubation up to 1 month
    5. Enteral phase produces abdominal discomfort
    6. Parenteral phase results in fever, myalgia, weakness, diarrhea, facial/periorbital edema, and eosinophilia
  2. Echinococcus granulosus
    1. Carnivorous animals are definitive hosts, grazing animals are intermediate hosts
    2. Ingestion of eggs from stool of definitive host
    3. Oncospheres are released in small intestine and travel hematogenously to other organs forming protoscolices and daughter cysts
    4. Most infections are asymptomatic
    5. Can cause: abdominal pain, hepatomegaly, chest pain, cough, hemoptysis, pneumonia, or anaphylaxis from cyst rupture
  3. Schistosoma hematobium, S. mansoni, S. japonicum (Schistosomiasis)
    1. Acquired through skin in freshwater during swimming or bathing
    2. Snail is definitive host, human is intermediate host
    3. Schistosomulae travel to portal veins in liver, develop into adults, and then migrate to veins of bladder or bowel/rectum
    4. Cercarial dermatitis 24 hours after exposure
      1. pruritic papular rash after swimming
    5. Acute schistosomiasis 1-2 months after exposure
      1. fever, chills, cough, headache, lymphadenopathy, hepatosplenomegaly
    6. Chronic schistosomiasis
    7. Symptoms: intestinal disease, fatigue, anemia, colitis, polyps, pipe-stem fibrosis of liver, and liver and bladder granulomas
  4. Wuchereria bancrofti, Brugia malayi, Onchocerca volvulus (Filariasis)
    1. Humans are definite host, insects are obligate intermediate host
    2. Transmitted through insect bites
    3. Spread through lymph or subcutaneously
    4. W. bancrofti and B. malayi
      1. usually asymptomatic
      2. acute adenolymphangitis: fever, painful lymphadenopathy
      3. lymphedema: caused by obstruction of lymphatics by adult worm
      4. tropical pulmonary eosinophilia produces recurrent asthma
    5. O. volvulus
      1. dermatitis: host reaction to migrating larvae
      2. subcutaneous nodules
      3. ocular keratitis can lead to blindness