Exam #5: GI Helminths Flashcards
What are nematodes? What are the general characteristics of roundworms?
Roundworms
- Cylindrical shaped (ala round worms)
- Non-segmented
- Separate sexes
- Complete digestive system
- Covered in a protective cuticle
*Note that you need to be infected by BOTH sexes to have infection
How are helminth infections diagnosed?
Egg morphology
Where are helminth infections most common in the US & why?
- Southeastern US
- Climate is best for egg growth
What does it mean that “adult worms do NOT replicate in man?”
- Adult worms have “sex” in the intestines & you shed the eggs
- However, the number of adults will NOT increase
What eosinophila an indication of?
Helminth infections i.e. Nematode infection that has passed to other tissues from the GI tract
What is the most common helminthic infection encountered in the US?
Enterobius vermincularis (pinworm)
What are Geohelminths?
Nematode infections acquired through contact with infected soil
What is Enterobius vermincularis? What are the characteristic egg shape? What is enterobiasis?
Enterobiasis is the name of the disease caused by Enterobius vermincularis, or the pinworm.
- Pinworm
- Eggs are flat on one side
*This is the most common helminth infection in the US.
Describe the lifecycle of Enterobius vermincularis.
- Infected individual sheds eggs into environment
- Another individual ingests eggs
- Eggs hatch in the small intestine & then travel to the large intestine, where they mature
- Adult forms mate in the large intestine
- At night females come out of the rectum & lay eggs
*Note that some eggs can become airborne
What is the mode of transmission for Enterobius vermincularis?
- Fecal-oral
- Children most commonly self-infect by ingestion after scratching the anal or perianal region
*Note that reinfection & transmission to family is common. Also, the pinworms of other animals e.g. dogs, do NOT transmit to humans
What are the symptoms of Enterobius vermincularis infection?
- Typically asymptomatic
- Perianal itching (Pruritus)
How are Enterobius vermincularis infections diagnosed?
“Scotch tape test”
- Identification of eggs in perianal region
- Eggs are flatter on one side than the other
*Sometimes adult worms can be seen in the perianal region at night
How is Enterobius vermincularis infection treated?
Treatment is with several anti-helminthic compounds (mebendazole, pyrantel pamoate)–usually a single dose followed by another dose 2 weeks later
List the “Geohelminths.” How are these helminths commonly separated?
Ingestion of infectious eggs found in soil:
- Ascaris
- Trichuris
Active penetration of the skin:
- Strongyloides
- Hookworms
What is Trichuriasis? What causes Trichuriasis?
Trichuriasis is more commonly referred to as whipworm infection. Specifically, the causative organism is Trichuris trichuria.
*Name comes from the shape of the large female worm
Describe the life cycle of Trichuris trichiura.
- Eggs are excreted out of an infected individual
- Contamination of soil with infective eggs
- Ingestion from soil
- Eggs hatch in the small intestine & mature
- Travel to large intestine & attach/ reproduce to make more eggs
Where is Trichuris trichiura commonly seen in the US?
Mostly seen in the tropics, but can be found in the southeast US
How is Trichuris trichiura transmitted?
Fecal-oral (contaminated soil)
What are the symptoms of Trichuris trichiura infection?
90% are asymptomatic; however, in symptomatic patients:
- Bloody, mucus containing diarrhea
- Frequent stool
- Tenesmus (urge to defecate) in absence of stool
- Rectal prolapse
- May contribute to growth retardation & anemia
*One of the most frequently identified causes of recurrent rectal prolapse & children with high worm loads can appear emaciated & anemic
How is Trichuris trichiura diagnosed?
Identification of eggs in stool that are:
- Thick walled
- Barrel shaped with plugs at each end
What is Ascaris lumbricoides? What does Ascaris lumbricoides cause?
- Ascaris lumbricoides causes Ascariasis
- Largest nematode infection (foot long & diameter of a pencil)
Describe the lifecycle of Ascaris lumbricoides.
- Ingested eggs hatch & molt in the small intestine (like other nematode infections)
- However, larvae penetrate the intestine & enter the bloodstream
- From the bloodstream, larvae invade the lung alveoli
- Larvae then “crawl” up the trachea to the glottis & are swallowed
- Larvae then travel back to the small intestine where they mature into adults
Ascaris lumbricoides is associated with migration out of the GI tract. How does this manifest?
Eosinophilia
What are the symptoms caused by Ascaris lumbricoides infection? What are the clinical manifestations of intestinal & pulmonary infection?
Most are asymptomatic; however, symptoms can range from abdominal discomfort to death:
Intestinal symptoms are due to physical presence
- Abdominal pain
- dyspepsia
- appetite loss
- vomiting
- diarrhea
Pulmonary symptoms
- Mild cough
- Pneumonitis resembling asthma attack
How are Ascaris lumbricoides infections transmitted?
Fecal-oral; soil contaminated with human feces
How is Ascaris lumbricoides infection diagnosed?
GI= eggs in stool that are oval with a bumpy surface
Pulmonary=
- Observation of larvae in sputum
- Eosinophils in sputum
What causes Hookworm infections? Where are these organisms most endemic?
- Necator americaus (Southeastern US)
- Ancylostoma duodenale (Tropics)
Describe the lifecycle of the Hookworms.
- Eggs hatch in soil, releasing larvae
- Larvae in soil mature and become infectious forms (filariform)
- Can attach to skin & penetrate into the tissue, or enter via hair follicle
- Larvae migrate through the lymphatics to the bloodstream
- From the bloodstream they travel to the alveoli
- Like Ascaris they then ascend the trachea & are eventually swallowed, leading them to the small intestine
- Production of eggs occurs in the small intestine
Worms consume blood!
What can Hookworm infection cause?
Anemia (consumption of blood)
*Note that this is particularly concerning in children & pregnant women
Can dog and cat hookworms can infect humans?
Yes, but they do not have the systemic effects that human hookworms do.
Rather, they cause “Cutaneous larval migrans”
What are the clinical manifestations of Hookworm infection?
- Iron-deficiency anemia
- Protein malnourishment
- Moderate dermaitis
- Pneumonia
- Eosinophila
What does Strongyloides stercoralis cause?
Strongyloidasis
What is unique about Strongyloides stercoralis ?
Facultative–can replicate in the host & in the environmentally, independently
- Larvae shed
- Replication in the soil
- Smallest
Describe the lifecycle of Strongyloides stercoralis .
Same as hookworms for parasitic infection, except there are NO MALES, ONLY FEMALES!
What are the symptoms of Strongyloides stercoralis infection?
- Little worm burden= little symptoms
- Pulmonary stage may provoke pulmonary inflammation & eosinophilia
When is Strongyloides stercoralis hyper-infection most commonly seen?
Immunosuppressive therapy (glucocorticoides)
What are the symptoms of Strongyloides stercoralis hyperinfection & disseminated infection?
Hyper-infection= worsening of pulmonary & GI symptoms
Disseminated infection= CNS, peritoneum, liver, & renal infection
