Flashcards in Exam #5: Parasitic Infections of the GI Tract Deck (37):
What parasitic infection of the GI tract is most commonly diagnosed in the US?
Giardia lamblia (duodenalis)
What are the four classes of protozoa? How are they classified?
Sporozoans= gliding ("tank tread")
How do most protozoa reproduce?
Asexually by binary fission
Important because you only need to be infected by one parasite & then there is exponential growth; also, v. low infectious dose
What is the cyst form of a protozoa?
An environmentally protected form of a parasite
- Resistant to UV light
- Resistant to drying out
- Allows for passage through the acidic pH of the stomach
What is Amebiasis? What causes it? What is the typical presentation of Amebiasis?
Amebiasis is the disease caused by amebae infection. The organism that causes amebiasis is Entamoeba histolytica.
Typical presentation is diarrhea/ dysentery.
What are the two forms of Entamoeba histolytica?
Trophozoic= unstable in environment & can be killed by acid pH of stoamch
Cyst= stable/ resistant (this is the form that is transmissible & found in the environment)
Describe the lifecycle of Entamoeba histolytica.
- Infected individual excretes cyst & trophozoic forms of Entamoeba histolytica
- Cyst is transmitted from infected individual to environment, and then to new host
- In host it "excysts"
- Invades the wall of the colon and multiples
Can cause intestinal disease or extraintestinal disease (liver abscess)
Which form of Entamoeba histolytica is more infectious in terms of symptoms?
Asymptomatic infection= mainly cyst
Symptomatic infection= trophozite that is readily destroyed in the environment.
What are the symptoms of Entamoeba histolytica infection?
Dysentery (bloody & mucousy diarrhea)
What is the difference between Entamoeba histolytica dysentery & bacterial?
Fever--no fever in Entamoeba histolytica
What type of lesion does Entamoeba histolytica cause in the intestinal wall?
What symptoms can be caused by spread of Entamoeba histolytica to the bloodstream?
Liver abscess (abdominal pain)
The amoeba basically perforates the bowel & intestinal bacteria are transmitted through the blood to other areas on the body
How is Entamoeba histolytica diagnosed?
- Stool examination (ova & parasite ordered)
- Antigen detection
- Biopsy or Serology for extra-intestinal
How is Entamoeba histolytica infection prevented? How is it treated?
Sanitation & hygiene prevent disease
Treatment is Metronidazole (Flagyl)
What is the morphological features that distinguishes Entamoeba histolytica?
What is Giardiasis? What organism causes it?
Giardiasis is one of the most common diseases caused by intestinal protozoa, and specifically, it is caused by a flagellated protozoa, Giardia lamblia. Characteristics of Giardia lamblia include:
- 2x nuclei
- Sucker that makes it stick to the intestinal epithelium
Most common parasitic infection in the US
Describe the lifecycle of Giardia lamblia.
- Ingestion of cyst
- Multiplies by binary fission
- Trophozites are NOT invasive, but can absorb nutrients from the bowel
Does NOT invade-->just get diarrhea
When is Giardia lamblia commonly seen?
The cyst form of Giardia Lamblia is relatively resistant to standard water treatment procedures; thus, US outbreak are commonly associated with contaminated water.
Also, infection is more common in the young (<10)
*Note that peak transmission is in the summer months, & infection is most commonly acquired by drinking untreated surface water while hiking or camping
What are the symptoms of Giardia lamblia?
Acute disease leading to sudden:
- Abdominal cramping
*Malabsorption that leads to:
- Floating stool
*NO blood & NO fever
Note that chronic disease can lead to malnutrition
How do the symptomatic & asymptomatic invidiauls compare with Giardia lamblia infection?
Symptomatic= more trophozites
How is Giardia lamblia diagnosed?
Observing cysts in stool
Observing trophozites in diarrhea
Fecal antigen detection (commercial assay)
What is the only ciliated parasite that infects humans? What does it cause?
Balantidium coli is the only ciliated parasite to infect humans, and infection causes Balantidiasis.
Describe the lifecycle of Balantidium coli.
Basically the same as the others.
- Cyst form is ingested
- Excystation occurs in small intestine
- Trophozites can colonize the large intestine, or invade the walls of the colon
What are the symptoms caused by Balantidium coli infection? What is it similar to? How do you tell the difference?
- Can lead to dysentery diarrhea
- Presentation is identical to Entamoeba hystilica i.e. amebic dysentery; however, as the primary host is pigs, Balatidiasis is more commonly associated with those that work with pigs
What is Cryptosporidiosis? What causes it?
Cryptosporidosis is the disease caused by sporozoan infection, specifically, Cryptosporidium parvum.
Describe the lifecycle of Cryptosporidium parvum.
Sexual & asexual reproduction
- Unlike the others
- Ingest oocyst (cyst produced by sexual reproduction) that excysts in the small intestine, releasing sprozoites
- Sporozites penetrate and infect intestinal epithelial cells, where they differentiate into trophozoites
How does Cryptosporidium parvum stain?
Modified acid fast staining protocol detects fresh oocysts in stool samples
*note that it was the development of this staining protocol that led to the realization that this was much more prevalent than originally thought
What is a reservoir of Cryptosporidium parvum?
*This is the only parasite so far that has a true reservoir so far
What is the connection between Cryptosproidium and AIDS?
15-20% of AIDS patients with diarrhea have Cryptosporidium positive stool. Because of the prevalence of the disease, prophylaxis has become routine.
What are the symptoms of Cryptosporidium parvum infection?
Profuse watery diarrhea
*Note that generally this is self-limiting, but in the severely immunosuppressed it can lead to severe dehydration & death
What is Isospora belli? What does it cause?
Sporozoan/ cocyst based disease that is increasingly diagnosed in immunosuppressed individuals i.e. the second most common cause of chronic diarrhea in AIDS patients (to Cryptosporidium)
What are the symptoms of Isospora belli in AIDS patients?
What is Cyclospora? What is it associated with?
Cyclospora cayetanesis is the causative agent of Cyclosporiasis, another sporozoan caused GI disease. Infection has been associated with contaminated water & contaminated raspberries imported from Guatemala.
What are the symptoms of Cyclospora?
Profuse watery diarrhea
*Generally more severe & of longer duration in AIDS patients
How is Cyclospora diagnosed?
- Pink staining oocysts that look like Cyrptosporidium (with modified acid fast stain
- However, Cyclospora oocysts FLOURESCENT under UV light
*Note that cryptosporidium parva does NOT flouresce under UV light
What is microsporidiosis? What is it caused by?
Microsporidosis is an intestinal disease caused by Microsporidia.