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Micro Exam 5: GI Nematodes

Terms in this set (36)

Stages of Development:
Ova: nonoperculated
Rhabditoform larva
Filariform larva
Intestinal Nematode (Roundworm)
What are the 5 intestinal nematodes?
Ascaris lumbricoides
Enterobius vermicularis
Hookworm (A. duodenale, N. americanus)
Strongyloides stercoralis
Trichuris trichiura
- Giant intestinal worm
- up to 1,500 worms/host
Ascaris lumbricoides
- blockage of intestinal lumen
- localized hemorrhage & edema
- appendicitis
- ascarid pneumonitis
Ascaris lumbricoides
Visceral larval migrans
Toxocara canis; Toxocara cati
Ascaris lumbricoides -- habitat, intermediate host, reservoir host, mode of infection?

NO intermediate host
habitat -- small intestines
reservoir host -- swine
mode of infection -- ingestion

NO intermediate host
Infective -- mature embryonated egg (ingested)
Diagnostic -- (1) decorticated ova or corticated ova in feces (either fertilized or unfertilized); (2) adult male and female worms (intestines or feces)
Ascaris lumbricoides
- eggs are passed in feces
- mature (fertilized) egg ingested by man
- eggs hatch = infective larva invade intestinal mucosa
- carried via portal, systemic cirucation to the lungs
- larvae mature further in the lungs (10-14 days), penetrate the alveolar walls, ascend the bronchial tree to the throat, and are swallowed
- develop into adult worms in the small intestines
Ascaris lumbricoides (giant intestinal worm) -- lifecycle
- most pts asymptomatic
- some develop pulmonary symptoms during lung migration phase
- mild abdominal discomfort, dyspepsia, loss of appetite, and nausea may occur
- affects intellectual development, cognitive performance and growth
Ascaris lumbricoides (giant intestinal worm) -- symptoms
- secretes molecules that modulate lymphocyte proliferation and cytokine production
- depresses appetite and food intake by children, interferes with absorption of proteins, fats, lactose, Vit. A, and iodine
Ascaris lumbricoides (giant intestinal worm) -- S&S
Ascaris lumbricoides: specimen processes and laboratory identification (identifiable forms)
specimen: feces

ID form:
1. Decorticated ova -- oval/round; hyaline to light brown; yolk mass
2. Corticated ova -- oval, elongated, rectangular; brown cortication, hyaline shell wall; yolk mass
OVAs: fertilized = organized and pulled-away from shell wall; unfertilized = disorganized mass that fills the shell
3. Adult -- round and slender, male has curved tail; creamy-white color with pinkish cast; 3-lipped buccal structure
most prevalent helminth infection; geographical distribution
Ascaris lumbricoides
pinworm or "seatworm"
Enterobius vermicularis
- frequently asymptomatic
- mild to severe itching of perianal and vaginal region
- occasional appendicitis
- anxiety, insomnia, and irritability = psychological component
Enterobius vermicularis (pinworm) -- S&S
Enterobius vermicularis -- habitat, mode of infection?

NO intermediate host
NO reservoir host
habitat -- large intestine, cecum
mode of infection -- ingestion of embryonated egg

NO intermediate/reservoir hosts = "parasite of man"
Enterobius vermicularis: Infective and Diagnostic forms
Infective -- embryonated egg, Rhabditoform larva (ingestion)
Diagnostic -- eggs on perianal folds, larvae insdie the eggs mature within 4-6 hrs
eggs can become aerosolized and inhaled or ingested
Enterobius vermicularis
1. eggs deposited into perianal folds; self-infection by hand-to-mouth; transmission by handling contaminated items, surfaces, aerosolized eggs
2. ingestion of infective eggs
3. larvae hatch in small intestine
4. adults "establish themselves" in colon/cecum
5. gravid females migrate nocturnally outside the anus and oviposit while crawling on the skin of the perianal area
Enterobius vermicularis (pinworm) -- Life Cycle
- invasion period: ground itch; larval penetration
- pulmonary phase: pneumonitis; due to larval irritation
Ancylostoma duodenale (Old World Hookworm) OR Necator americanus (New World Hookworm) -- pathology
- intestinal phase: anemia, desquamation (skin peeling), malnutrition, sequelae (i.e. secondary bacterial infection)
- creeping eruption, pruritis (itchy skin), ground itch (pruritic maculopapular rash)
- transient pneumonitis during migration
- epigastric pain, diarrhea, anorexia, eosinophilia (30-45 days post infection)
- physical, cognitive, intellectual growth diminished in children
Ancylostoma duodenale (Old World Hookworm) OR Necator americanus (New World Hookworm)
Ancylostoma duodenale (Old World Hookworm): specimen processes and laboratory identification (identifiable forms)
Specimen: feces

ID Form:
1. Ova: oval with bluntly rounded ends, hyaline color, yolk mass usually in cleavage, thin/single shell wall

2. Rhabditiform larvae: large buccal cavity (longitudinal parallel lines), genital primordium (small), slender/long/tapering tail

3. Adult (different from N. americanus): cylindrical; dorsally curved head; grayish-white color; buccal structures (two fused, sharp "teeth" on each side of ventral surface); male copulatory bursa (paired copulatory spicules=separated, small paired dorsal rays=tripartite)
- eggs passed in feces (diagnostic form)
- Rhabditiform larva hatches
- Filariform larva
- Filariform larva penetrates skin (infective form)
- Adults in small intestines
Ancylostoma duodenale (Old World Hookworm) OR Necator americanus (New World Hookworm) -- Lifecycle
+Ancylostoma duodenale (Old World Hookworm) and Necator americanus (New World Hookworm) -- Infective and Diagnostic forms
infective form -- rhabditiform larva (penetrates skin)
diagnostic form -- eggs in feces
Auto-infection and multiplication w/in host
Strongyloides stercoralis (threadworm)
Two types of cycles:
(1) Free-Living Cycle -- free living adult male/females mate and produce eggs (outside of host), rhabditiform larvae hatch, become infective filariform larvae which exist in soil and penetrate human host skin=pneumonitis (blood-lung-intestinal route)
(2) Parasitic Cycle -- migrate to SI (molt twice and become adult female worms), live in SI epithelium and produce eggs, yield rhabditiform larvae, passed in stool
(3) Autoinfection -- rhabditiform larvae become infective filiform larve in SI --> penetrate intestinal wall and disseminate throughout body (without exiting the body)
Strongyloides stercoralis (threadworm) -- lifecycle
Autoinfection -- rhabditiform larvae become infective filiform larve in SI --> penetrate intestinal wall and disseminate throughout body (without exiting the body)
Strongyloides stercoralis (threadworm)
- males are either eliminated early in the parasitic cycle, or the gravid females enter the mucosa and deposit their eggs through parthenogenesis (asexual reproduction in which the offspring develops from unfertilized eggs)

- Rhabditiform larvae molt into filariform larvae in the intestine * penetrate the intestinal wall to enter the blood stream initiating subsequent internal autoinfective cycles
Strongyloides stercoralis (threadworm)
Strongylooides stercoralis -- habitat, reservoir host, mode of infection?

NO intermediate host
habitat -- small intestine
reservoir host -- dogs or apes
mode of infection -- active penetration of skin

NO intermediate host
Strongylooides stercoralis-- Infective and Diagnostic forms
Infective -- filariform larvae
Diagnostic -- rhabditiform larvae passed in the stool
- skin portal of entry = petechial hemorrhage, pruritis
- larval migration = high eosinophilia, sensitization reaction
- intestinal infection = desquamation, severe diarrhea/gastroenteritis, anemia, weight loss, hyperinfection may be fata in immunosuppressed pts
Strongylooides stercoralis-- Pathology

(GI Nematodes)
- autoinfective can build large numbers in victim = high worm burden
- some infections documented to last > 60 yrs
- person to person transmission possible
- epigastric pain, fluctuating eosinophilia, recurrent maculopapular rash of buttocks, perineum, and thighs
Strongylooides stercoralis-- Pathology

(GI Nematodes)
- asymptomatic to severe disease; secondary bacterial infection
- worm secretes protein; forms pores in lipid bilayers that allow anterior end to embed in epithelium
- localized inflammation and bleeding
- iron deficiency anemia in heavy infection
- heavy infections = chronic abdominal pain, diarrhea, growth retardation, clubbing of fingers
- bloody stools, recurrent rectal prolapse
- growth retardation and impaired cognitive function
Trichuris trichiura (Whipworm) -- pathology
Trichuris trichiura (whipworm) -- habitat, mode of infection?

NO intermediate host
NO reservoir host
Habitat -- large intestines, cecum
Mode of Infection -- ingestion
Trichuris trichiura (whipworm) -- Infective and Diagnostic forms
Infective Form -- mature embryonated egg
Diagnostic Form -- unembryonated eggs passed in feces
- perforation of intestinal wall
- peritonitis (Inflammation of the membrane lining the abdominal wall and covering the abdominal organs)
- rectal prolapse
Trichuris trichiura (Whipworm) -- pathology
Trichuris trichiura (whipworm) -- Diagnosis
specimen: feces

ID Form:
1. Ova: football, barrel-shape w/ bipolar plugs; golden brown; yolk mass
2. Adult: thick posterior and whip-like anterior; flesh-colored; ID at colonoscopy
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