L37: Parasitic Roundworm Infections of the GI Tract Flashcards
3 types of helminths
- Nematodes (roundworms) – non-segmented bodies, separate sexes, complete digestive system
- Cestodes (tapeworms) – segmented bodies, hermaphroditic, absorb nutrients
- Trematodes (flukes) – non-segmented/leaflike, hermaphroditic, primitive gut
General facts about GI nematodes
Most common parasitic helminths in the US/world, not usually fatal, common in areas with poor sanitation (particularly developing tropics), caused by presence of adult forms in body – common in SE US
Life cycle of nematodes
Egg –> multiple larval stages –> adult stages
- -Separate sexes, female is larger than male
- -Adult worms do not replicate in humans
- -Lead to eosinophilia
Geohelminths
Nematode infection acquired through contact with infected soil due to larvae/eggs needing to develop in warm soil
Enterobius vermicularis (pinworm)
Most common helminthic infection in US, flat-sided eggs, hang out in butt hole
Transmission of pinworm
Fecal-oral due to ingestion of eggs which hatch and develop in the intestines – reinfection and transmission within families are both common – animal pinworms do not infect humans
Symptomatic infection of pinworm
Perianal itching (can lead to secondary bacterial infection) and potential appendicitis – most infections are asymptomatic
Diagnosis of pinworm
Identification of eggs in perianal region (flat-sided, use tape to see them)
Control and prevention of pinworm
Anti-helminthic compounds such as mebendazole, pyrantel pamoate – single dose, repeated later – must treat ALL household members
Trichuris trichiura (whipworm)
Named for shape of eggs (side kind of looks like a whip)
Life cycle of Trichuris trichiura (whipworm)
Infected individual passes eggs in stool, mature in the soil/environment then consumed, hatch in intestines and develop in mucosa
Epidemiology of Trichuris trichiura (whipworm)
1/4 of the world infected, mostly in tropical regions (SE US), 90% asymptomatic
Transmission of Trichuris trichiura (whipworm)
Fecal-oral from contaminated soil
Symptomatic infections of Trichuris trichiura (whipworm)
Often due to heavy worm burden (>200) and causes bloody, mucus-containing diarrhea, frequent stools, rectal prolapse, growth slowing, and anemia in kids
Diagnosis of Trichuris trichiura (whipworm)
Identification of eggs in stool (look like handles of whips on the sides)
Control and prevention of Trichuris trichiura (whipworm)
Proper sanitation and personal hygiene
Ascaris lumbricoides
Cause ascariasis, largest of the intestinal nematodes and forms tangles of worms that can cause physical obstruction or blockage
Life cycle of Ascaris lumbricoides
Infected individuals pass lumpy bumpy eggs that develop outside of human and get ingested – get into liver and lungs (eosinophil count in these locations is important) – takes over a month
Transmission of Ascaris lumbricoides
Fecal-oral; soil contaminated with human feces – eggs must develop in soil first – HUMANS ARE ONLY RESERVOIR – most infections asymptomatic
Symptoms of Ascaris lumbricoides
Range from abdominal discomfort to death – physical presence of adult worms in small intestine can lead to abdominal pain, indigestion, loss of appetite, vomiting, diarrhea – physical obstruction can occur
Pulmonary disease of Ascaris lumbricoides
Combination of physical presence of larvae and immune response – mild cough, pneumonitis
Diagnosis of Ascaris lumbricoides
Lumpy bumpy eggs in stool, larvae or eosinophils in sputum
Control and prevention of Ascaris lumbricoides
Sanitation and hygiene
What are the two types of hookworm?
Necator americanus and Anclylostoma duodenale
Life cycle of hookworm/Necator americanus/Anclylostoma duodenale
Larvae form in the soil from eggs, takes a few weeks to mature but then alive in soil, can break through the skin and then get swallowed
Epidemiology of hookworm/Necator americanus/Anclylostoma duodenale
Major cause of anemia (especially children and pregnant women), found in SE US
Transmission of hookworm/Necator americanus/Anclylostoma duodenale
Larvae from fecal contaminated soil penetrate intact skin – no animal reservoir for human hookworms
Disease of hookworm/Necator americanus/Anclylostoma duodenale
Cause iron-deficiency anemia due to blood loss from feeding; protein malnourishment; penetration of the skin can lead to moderate dermatitis; pneumonia and eosinophilia – Ancylostoma consumes more blood than Necator
Diagnosis of hookworm/Necator americanus/Anclylostoma duodenale
Presence of eggs in stool (distinguishing between two species requires looking at adult worms/larvae)
Prevention and control of hookworm/Necator americanus/Anclylostoma duodenale
Sanitation and wearing shoes
Strongyloides stercoralis
Smallest intestinal nematode, found in SE US and Appalachia – first example of facultative parasite (can multiply and exist as free-living nematode in the soil)
Life cycle of Strongyloides stercoralis
Infected individual is actually passing larvae through stool then develops into free-living adult in the soil and produces eggs there – mature larvae can also penetrate before they leave the intestines and cause a hyperinfection
Transmission of Strongyloides stercoralis
Penetration of skin by infectious larvae
Symptomology of Strongyloides stercoralis
Low worm burdens lead to little symptomology (epigastric pain and tenderness, bloating, heartburn) – pulmonary stage of infection can provoke pulmonary inflammation and eosinophilia
Hyperinfection of Strongyloides stercoralis
- -Due to abrogation of immune defenses – increased numbers of filariform larvae leave the intestine –> worsening of diarrhea and pulmonary symptoms
- -Disseminated infections can also occur which causes migration of larvae all around body
Diagnosis of Strongyloides stercoralis
Detection of LARVAE in stool
Control and prevention of Strongyloides stercoralis
Sanitation and hygiene and wearing shoes
Know your eggs!
Flat on one side = Enterobius vermicularis
Lemon/barrel (like a whip handle) = Trichuris trichiura
Lumpy bumpy = Ascaris lumbricoides
Boring/plain = hookworm
Larvae instead of eggs in stool = Strongyloides stercoralis
