Amebiasis Pathogenesis

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Questions and Answers

What happens to trophozoites in the presence of ambient oxygen concentration?

They remain dormant

They multiply rapidly

They are killed (correct)

They change shape

Where is the primary site of infection for E. histolytica?

Lungs

Liver

Large intestine (correct)

Brain

What is the main source of water and food contamination by E. histolytica?

Poor sanitation

Symptomatic carriers (correct)

Contaminated utensils

Asymptomatic carriers

What is the primary mode of transmission of E. histolytica?

Fecal-oral route Signup and view all the answers

What is the result of the epidemic form of amebiasis?

Direct person-to-person contact Signup and view all the answers

What is the habitat of Entamoeba gingivalis?

Mouth and gums Signup and view all the answers

What is the habitat of Iodamoeba buetschili?

Large intestine Signup and view all the answers

What is the result of invasion into the deeper mucosa by E. histolytica?

Extension into the peritoneal cavity Signup and view all the answers

Which of the following is NOT a common source of parasitic infection?

Infected hospital equipment Signup and view all the answers

What is the primary mode of transmission of balantidiasis?

Fecal-oral transmission Signup and view all the answers

What is the characteristic feature of the trophozoite of Balantidium coli?

Presence of cilia Signup and view all the answers

What is the drug of choice for the treatment of balantidiasis?

Tetracycline Signup and view all the answers

What is the most common helminthic infection in humans?

Hookworm infection Signup and view all the answers

What is the primary consequence of helminthic infections in children?

Reduced academic performance Signup and view all the answers

Which of the following is a complication of intestinal balantidiasis?

All of the above Signup and view all the answers

What is the common route of transmission of Enterobius vermicularis?

Auto-infection Signup and view all the answers

What is the typical structure of the trophozoite of Dientamoeba fragilis?

Typical of a flagellate Signup and view all the answers

Which stage of Dientamoeba fragilis has not been described?

Cyst stage Signup and view all the answers

What is the most common mode of transmission of Dientamoeba fragilis?

Faecal-oral route Signup and view all the answers

What is the therapeutic agent of choice for Dientamoeba fragilis infection?

Iodoquinol Signup and view all the answers

Which of the following flagellates is considered to be non-pathogenic?

Trichomonas hominis Signup and view all the answers

What is the shape of the trophozoite of Trichomonas tenax?

Pyriform shape Signup and view all the answers

Which of the following flagellates has both a trophozoite and cyst stage?

Chilomastix mesnli Signup and view all the answers

What is the primary location where Chilomastix mesnli lives?

Cecum Signup and view all the answers

Study Notes

Pathogenesis of Amebiasis

Trophozoites divide and cause extensive local necrosis in the large intestine
Invasion into the deeper mucosa can lead to secondary involvement of other organs, primarily the liver, lungs, brain, and heart
Extraintestinal amebiasis is associated with trophozoites

Epidemiology of Amebiasis

E. histolytica has a worldwide distribution, with highest incidence in tropical and subtropical regions with poor sanitation and contaminated water
90% of infections are asymptomatic, while the remaining produce a spectrum of clinical syndromes
Patients infected with E. histolytica pass non-infectious trophozoites and infectious cysts in their stools, making them the main source of water and food contamination
Symptomatic amebiasis is usually sporadic, while epidemic form is a result of direct person-to-person faecal-oral spread under conditions of poor personal hygiene

Non-Pathogenic Protozoa

Entamoeba gingivalis:
- Lives primarily on exudate from the margins of gums
- Thrives best on unhealthy gums
- Can be transferred by kissing, using contaminated utensils, or droplet spray of the mouth
- Can be treated or prevented by proper care of the teeth and gums
Entamoeba coli:
- Transmitted through fecal contamination
- Depends on personal hygiene
Endolimax nana:
- Lumen dweller in the large intestine
- Results from ingestion of viable cyst in polluted water or contaminated food
Iodamoeba buetschili:
- Natural habitat is the lumen of the large intestine, primarily in the caecum
- Natural parasite of man and lower primates

Symptoms of Amoebiasis

Diarrhea/Dysentery
Nausea
Abdominal Pain
Ulceration of the intestinal mucosa

Life Cycle and Laboratory Diagnosis

Microscopic examination of faeces for trophozoite and cysts
Trophozoite is very large, varying in length from 50 to 200μm and in width from 40 to 70μm
Surface is covered with cilia

Treatment

Drug of choice is tetracycline
Alternative agents are iodoquinol and metronidazole

Medical Helminthology

Concerned with the study of helminthes or parasitic worms
Helminthes are trophoblastic metazoa (multi-cellular organisms)
Causes of high morbidity and mortality worldwide
Causes anemia and malnutrition
Reduces academic performance in children
Causes economic loss in domestic animals

Introduction to Helminthes

Age-dependent distribution of infections from geo-helminthes and schistosomes
Children disproportionately carry the burden of schistosomes and geo-helminthes
Sources of parasites include:
- Contaminated soil (Geo-helminthes)
- Water (cercariae of blood flukes)
- Food (Taenia in raw meat)
- Blood sucking insects or arthropods (as in filarial worms)
- Domestic or wild animals harboring the parasite (as in echinococcus in dogs)
- Person to person (as in Enterobius vermicularis, Hymenolopis nana)
- Oneself (auto-infection) as in Enterobius vermicularis

Dientamoeba fragilis

Initially classified as an amoeba, but internal structures of the trophozoite are typical of a flagellate
No cyst stage has been described
Worldwide distribution
Transmission occurs through faecal-oral routes
Most infections are asymptomatic, with colonization of the cecum and upper colon
Symptoms include abdominal discomfort, flatulence, intermittent diarrhea, anorexia, and weight loss
Therapeutic agent of choice is iodoquinol, with tetracycline and paromomycine as acceptable alternatives

Other Flagellates

Trichomonas hominis:
- Lives in the caecal area of the large intestine
- Feeds on bacteria
- Considered to be non-pathogenic
- Transmission occurs in the trophic form
- No treatment is indicated
Trichomonas tenax:
- Recovered from the mouth, specifically in tartar from the teeth
- No known cyst stage
- Trophozoite has a pyriform shape and is smaller and more slender than that of T. hominis
- Diagnosis is based on the recovery of the organism from the teeth, gums, or tonsillar crypts
- No therapy is indicated
Chilomastix mesnli:
- Has both a trophozoite and cyst stage
- Lives in the cecal region of the large intestine, where the organism feeds on bacteria and debris
- Considered to be non-pathogenic
- No treatment is recommended

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Description

Learn about the pathogenesis of amebiasis, including the division of trophozoites, local necrosis, and potential involvement of other organs. Understand the role of anaerobic environments and oxygen concentration.