GI Protozoans Flashcards
How will infection with Giardia lamblia (aka G. intestinalis) present clinically?
Intermittent episodes of water diarrhea, NO BLOOD
May be asx or acute/ chronic diarrheal illness
G. lamblia is what type of disease?
Zoonotic
What populations are more greatly affected by G. lamblia?
Children, and problematic in IMC (no ability to build antibodies)
What is the most commonly identified intestinal parasite in the wold?
G. lamblia
What are the 2 morphological stages of G. lamblia?
Trophozoite and cyst
What is the most important structural element of G. lamblia?
Flagellate
Which morphological stage of G. lamblia is identified by the presence of 4 nuclei and contributes to protection of the organism?
Cyst
1 cyst produces 2 trophozoite, each trophozoite has 2 nuclei
Which morphological stage of G. lamblia is identified as teardrop shape with a bi-lobed ventral adhesive disc with 2 nuclei?
Trophozoite
The trophozoite form of G. lamblia feeds on mucus tissues and has what effect on tissues/ RBCs?
Does not invade tissue or destroy RBCs
How does G. lamblia become infectious?
Ingestion of the cyst from contaminated food/ water
highly contagious!
How does G. lamblia transition between the trophozoite and cyst stages? (5 steps)
- Ingest cyst (infectious)
- Excystation in stomach = trophozoite
- Trophozoite divides in small bowel
- Trophozoites in large bowel encyst
- Cysts passed into environment
Where is infection with G. lamblia most common?
Western states (Rocky Mountains) (contributes ~2.5 mill deaths in combo w malnutrition/ co-infection)
G. lamblia is an infectious disease (including as an STI). How many cysts are considered to be an infectious dose?
10-25 cysts, >25 cysts = 100% infection rate
How can infection with G. lamblia contribute to malnutrition?
Vitamin B12 deficiency
organism feeds on it
What are the virulence factors of G. lamblia? (2)
- Ventral disc implants (“sucker”)
2. Malabsorption of intestinal tissue
What is the gold standard for diagnosis of G. lamblia?
Microscopic visualization of cysts/ trophozoites in stool samples
(O&P = egg and parasite examination)
What may be necessary for diagnosis of G. lamblia due to the shedding of cysts?
Multiple stool samples
Why can serological tests be problematic for the identification of G. lamblia?
Antibodies can be carried for > 2 years
if antibodies present, you will always test positive
What is the prognosis of infection with G. lamblia?
Most pts asx, self-limited but re-infections possible (if you did not build protective antibodies)
How is infection with G. lamblia controlled?
Purified water, avoid fecal contamination
What pathogen is responsible for a protozoan illness that can result in colitis and liver abscess?
Entamoeba histolytica
many species but only one associated with human disease
What is the importance of E. dispar in relation to E. histolytica?
Does not cause disease but gets in the way of identifying E. histolytica (commensal)
What organism has a non-flagellated trophozoite form with 1 nucleus and an infectious cyst form with 4 nuclei?
E. histolytica
What does E. histolytica feed off that leads to an important clinical symptom?
RBCs (use as nutritional source) = bloody stool
How does the life cycle of E. histolytica continue after the ingestion of cysts?
Become trophozoites and colonize the colon
Trophozoites do not survive well in environment
Once the trophozoite form of E. histolytica colonizes the mucosa of the colon, it may encyst and be passed in feces or invade what?
Invade intestinal mucosal barrier and gain access to the blood stream = dissemination
What is important about the epidemiology of E. histolytica? (3)
- Tropical areas
- Passed via contaminated water/ food
- Reportable disease
Disease via E. histolytica can be initiated by a small number of cysts and has diverse manifestations. What clinical presentations are the most common?
Acute amoebic colitis/ bloody stools
Dysentery to extraintestinal manifestations
Amoeba of E. histolytica hydrolyze the intestinal lining which results in what?
Results in ulcers, R upper quadrant pain
large scale ulceration
What are the virulence factors of E. histolytica? (4)
- Lectin (adhesion)
- Phospholipases (disrupt host membranes)
- Amoebapore (host cell lysis)
- Cysteine proteases (“chew away” other proteins)
How is infection with E. histolytica diagnosed?
Trophozoites/ cysts in stool sample
Radiology for extraintestinal disease
(also ELISA or PCR)
How is infection via E. histolytica controlled?
Purify water (cysts resistant to chlorine), avoid fecal contamination
Although infection with Cryptosporidosis can be caused by multiple species, which species have humans as the only host?
Cryptosporidium hominis
C. parvum bovine and human hosts
What population is more commonly affected by Cryptosporidium and how are healthy individuals affected?
Children, self limiting diarrheal illness in healthy individuals
What organism has the following 2 morphological forms: oocytes and sporozoites?
Cryptosporidium
Which stage of Cryptosporidium is infectious and how does it multiply?
Oocytes = infectious, does not multiply outside of the host
The life cycle of Cryptosporidium involves binding to the receptors on small intestine epithelial cells followed by what?
Ingested into parasitophorous vacuole
Once Cryptosporidium organisms are inside the epithelial cells, the parasite undergoes sexual and asexual reproduction to form what?
Thin walled oocytes (asexual) = reinfection
Thick walled oocytes (sexual) = shed into environment
Identification of what on morphology is important to identify Cryptosporidium?
Parasitophorous vacuole
What is important about the epidemiology of Cryptosporidium?
Contaminated water, recreational water, pools (cysts resistant to chlorine)
When are the oocytes of Cryptosporidium infectious?
Immediately after excretion
What is the cardinal symptom of infection with Cryptosporidium?
Watery diarrhea
also pt severely wasted, ~2 weeks, common if IMC
How is infection via Cryptosporidium identified?
Isolation of oocytes in stool sample (acid-fast oocytes are round)
What is the causative agent of infection with Cyclosporiasis?
Cyclospora cayetanensis
How is Cyclospora cayetanensis transmitted?
Contaminated water and imported foods (esp fresh fruits and vegetables from Latin America)
When is Cyclospora cayetanensis infectious?
Not immediately, oocytes shed in feces and then MUST first sporulate/ survive in the environment
What are the oocytes of Cyclospora cayetanensis resistant to?
Chlorine
What is the most identifiable clinical presentation of infection with Cyclospora cayetanensis?
Explosive, non-bloody, watery diarrhea
How is infection with Cyclospora cayetanensis identified on microscopy?
Large oocyte identified in stool sample, acid fast postiive, autofluorescent oocyte
(much larger than Cryptosporidium)
What GI protozoan is characterized by the following:
Disease via ingestion of cysts from contaminated food/ water (from animal feces)
Large central vacuole surrounded by nuclei
Blastocystis hominis
What GI protozoan is characterized by the following:
Zoonotic (pigs), fecal matter
Can result in gut perforation (but no blood in stool)
Trophozoite and cyst forms contain MACROnucleus
Cilia evident on trophozoite
Balantidium coli
