Parasitology - Intestinal and Urogenital Protozoa

Question 1

What are the three types of helminths?

Answer 1

1. Nematodes (roundworms)
2. Trematodes (flukes)
3. Cestodes (tapeworms).

Helminths never take caution

Question 2

What are the different modes/routes of transmission of protozoa? [6]

Answer 2

1. Oral-faecal route (ingestion)
2. Contaminated water (Giardia infections)
3. Contact with infected cats (Toxoplasmosis)
4. Venereal route (sexual intercourse, Trichomonas vaginalis)
5. Insect bite (Malaria, Trypanosomiasis, Leishmaniasis)
6. Direct skin penetration (wound infection)

Question 3

What are the four types of pathogenic protozoa?

Answer 3

1. Sporozoa
2. Amoebae
3. Flagellates
4. Ciliates

Question 4

What are the types of intestinal and urogenital protozoa? [5]

Answer 4

1. Amoeba
2. Flagellates
3. Ciliates
4. Apicomplexa
5. Microsporidia

Question 5

Give an example of an intestinal and urogenital amoeba.

Answer 5

Entamoeba histolytica

Question 6

Give an example of an intestinal and urogenital flagellate.

Answer 6

Giardia lamblia (duodenalis)

Trichomonas vaginalis

Question 7

Give an example of an intestinal and urogenital ciliate.

Answer 7

Balantidium coli

Question 8

Give an example of an intestinal and urogenital apicomplexa.

Answer 8

Isospora belli

• Cryptosporidium* species
• Cyclospora* species

Question 9

What are the three major intestinal and urogenital protozoa?

Answer 9

1. Giardia lamblia
2. Entamoeba histolytica
3. Trichomonas vaginalis

Question 10

What organs are targeted by intestinal and urogenital protozoa?

Answer 10

• Oropharynx
• duodenum
• small bowel
• colon
• urogenital tract

Question 11

How are intestinal and urogenital protozoa prevented?

Answer 11

• Improved sanitation
• Chlorination, iodisation and filtration of water
• Improved public health knowledge and awareness

Question 12

Outline the main characteristics of amoebae. [3]

Answer 12

• Primitive unicellular microorganisms
• simple lifecycle (feeding stage and infective stage)
• most are commensal organisms (benefit from host without harm).

Question 13

Name some commensal amoebae.

Answer 13

• E.coli
• E.hartmanni
• E.dispar (indistinguishable from E.histolytica)
• E.gingivalis
• Endolimax nana
• Iodamoeba butschlii

Question 14

List some pathogenic amoebae.

Answer 14

• Entamoeba histolytica
• Entamoeba polecki
• Naegleria fowleri (opportunistic)

Question 15

Outline the epidemiology and transmission of Entamoeba histolytica.

Answer 15

Epidemiology:

• worldwide distribution, high incidence in tropical and subtropical regions (poor sanitation), cold regions (Alaska, Canada, Eastern Europe)
• 35-50 million cases of symptomatic disease, 100,000 deaths annually.

Transmission:

• pass trophoziotes and cysts in stool
• flies and cockroaches spread cysts
• anal-oral sexual practices.

Question 16

Outline the lifecycle of Entamoeba histolytica.

Answer 16

1. Cysts and trophoziotes passed in faeces
2. Mature cysts ingested
3. Excystation
4. Trophoziotes multiply
5. Some form cysts and exit host

Question 17

What are the clinical syndromes presented by Entamoeba histolytica?

Answer 17

Varies depending on the location in the host, extent of the tissue invasion.

1. Asymptomatic carrier
2. Symptomatic intestinal amoebiasis
   
   • amoebic colitis
   • amoebic dysentery
3. Symptomatic extra-intestinal amoebiasis
   
   • liver infection + abscesses

Question 18

How do you diagnose intestinal disease due to Entamoeba histolytica?

Answer 18

• cysts and/or trophoziotes in faeces or tissues
  
  • stool examination + microscopy
• sigmoidoscopy
  
  • aspirates or biopsies + microscopy

Diagnosis can be difficult as other parasites can look identical, such as E.dispar, a commensal protozoa. Antigen tests needed to distinguish the two.

Question 19

What are the differences between trophozoites and cysts?

Answer 19

Trophozoites:

• The feeding stage of the protozoa
• Is actively motile (pseudopode)
• Replicates by binary fission
• Exists in favourable environments

Cysts:

• Quiescent and resistant
• Infective stage
• Develops mutliple trophozoites in mature multinucleated cysts
• Exists in unfavourable conditions

Question 20

Outline amoebic colitis.

Answer 20

Amoebic colitis is an infection of the intestine which is a form of symptomatic intestinal amoebiasis. It has the following symptoms:

• Abdominal pain, cramping
• Diarrhoea, flatulence
• Chronic weight loss and anorexia
• Chronic fatigue

Secondary bacterial infection may develop after the formation of flask-shaped amoebic ulcers in the colon, cecum, appendix or rectosigmoid area of the intestine (mucosa).

Question 21

Outline amoebic dysentery.

Answer 21

Amoebic dysentery is an infection of the intestine which is a form of symptomatic intestinal amoebiasis. It occurs gradually and has the following symptoms over several weeks:

• Abdominal pain and tenderness
• Tenesmus (painful and sudden bowel evacuation)
• Diarrhoea
• Weight loss

Question 22

Outline symptomatic extra-intestinal amoebiasis.

Answer 22

Trophozoites migrate into the blood stream and are filtered by the liver where they take residence. This may result in right lobe liver abscess, associated with pain over the liver and fever.

Trophozoite extension through the diaphragm may cause pneumonitis -> Liver infection associated with cough.

Symptoms include: Weakness, weight loss, sweating, nausea, vomiting, constipation.

E. histolytica may also migrate to other organs (lung, spleen, skin, brain).

Question 23

How do you diagnose extra-intestinal disease?

Answer 23

• Serology, useful but cannot distinguish from current and past infections
• Non-invasive imaging (hepatic abscess)
  
  • Ultrasound
  • CT
  • MRI

Question 24

How do you treat and prevent Entamoeba histolytica?

Answer 24

• Metronidazole followed by iodoquinol for acute fulminating amoebiasis
• Adequate sanitation
• Education to sexual partners
• Education to travellers
• Chlorination and filtration of water supplies

Question 25

Outline the **epidemiology** and **characteristics** of ***Giardia lamblia***.

Answer 25

Giardia lambia is distributed **worldwide** and can be found in streams, lakes, contaminated food and **water**, and spread through unusual sexual practices. * The cysts are **resistant to chlorination**. * **200 million** cases per year * colonises upper **small intestine** and **duodenum (duodenalis)** * non-invasive, 50% asymptomatic. Transmitted through the **oral-faecal route**, trophozoites divide by **binary fission**.

Question 26

Describe the **lifecycle** of ***Giardia lambia***.

Answer 26

Typical **oral-faecal** transmission cycle 1. **Excretion** of **cysts** by host 1 2. **Ingestion** of **cysts** by host 2 3. **Excystation** in the **duodenum** (_low pH_) * Flagellar activity * Breakage of the cyst wall (proteases) * Release of the trophozoite * **Attachment** to intestinal epithelium (adhesive disk) * **Twisting motion** (4 pairs of flagella) 4. **Asexual replication of trophozoites** * (2 nuclei) =\> (4 nuclei) * Cytokenesis =\> 2 binucleated trophozoites 5. **Encystation** * The trophozoite rounds up * Detachment from the intestinal epithelium * Secretion of the cyst wall

Question 27

List the **symptoms** and **pathogenesis** of ***Giardia lambia***.

Answer 27

Symptoms: * ranges from mild diarrhoea to severe malabsorption syndrome. * chronic syndromes: weight loss, failure to thrive. * **1-4 weeks**: nausea, loss of apetite, **foul-smelling watery diarrhoea**, blood and mucous rare, abdominal cramps, flatulence, **foul sulphuric belching**. * Patient can spontaneously recover, except if there is an IgA deficieny. **Pathogenesis**: * **irritation** of intestinal epithelium * **inflammation** * **lactase deficiency**.

Question 28

Outline how you would **diagnose** a ***Giardia lambia*** **infection**.

Answer 28

* **Examine cysts** and **trophozoites** in stool after diarrhoea. * Examine stool specimen for **three days** * In negative, but highly suspected cases a duodenal aspiration/small intestine biopsy is needed. * **Immunological tests for faecal antigen** * Immunoelectrophoreis * ELISA * Chromatographic and Indirect immunofluorescent staining (88-98% sensitive)

Question 29

How do you **treat, control, and prevent** ***Giardia lamblia*** infections?

Answer 29

* Treat with **_metronidazole_** * Avoid contaminated water, food, and faeces * Boiled water/**iodine** treatment (chlorine not effective) * Pubic health awareness.

Question 30

Outline the main **characteristics** and **epidemiology** of ***Trichomonas vaginalis***.

Answer 30

* **Four flagella** and **undulating** (short, smooth, wave-like motion) **membrane**. * Exists _only_ as a **trophozoite** in urethras, the vaginas of women, and the prostate of men. **Epidemiology**: * **Worldwide** distribution * Transmitted through **sexual intercourse**, infants infected through mother's infected birth canal. * Prevalence in **developed countries**: 5-20% women, 2-10% men.

Question 31

Outline the **symptoms** of ***Trichomonas vaginalis** infection*.

Answer 31

* Most infected women are **asymptomatic** or have scant (not enough) watery vaginal discharge. * **Vaginitis**: itching, burning, painful urination. * Men are **asymptomatic carriers**. * Men **occasionally** experience urethritis, prostatitis.

Question 32

How would you **diagnose** a ***Trichomonas vaginalis*** infection?

Answer 32

* **Microscopic examination** of vaginal or urethral discharge for trophozoites. * **Monoclonal fluorescent staining**. * **PCR probes** and serological tests available.

Question 33

How would you **treat, prevent, and control** ***Trichomonas vaginalis***?

Answer 33

* Treat using **_metronidazole_** (both partners, resistance must be reported) * Good **personal hygiene** * **Safe sexual practices** (condoms)

Question 34

Describe the **morphology** and **epidemiology** of ***Balantidium coli***?

Answer 34

**Morphology**: trophozoite covered in **hair-like cilia**, has a **funnel-like cytosome**. **Epidemiology**: **worldwide** distribution, swine and monkey reservoirs, infection via the **faecal-oral route**, outbreaks associated with **contaminated food**.

Question 35

What are the clinical **symptoms** and **treatment** for ***Balantidium coli***?

Answer 35

**Symptoms**: abdominal pain and tenderness, nausea, anorexia, watery stools with **blood and pus**, ulceration of intestinal mucosa. **Treatment**: **_tetracycline_**, metronidazole alternative.

Question 36

Desribe the **lifecycle** of ***Balantidium coli***.

Answer 36

Question 37

What are the main **similarities** and **differences** between *Giardia lamblia*, *Entamoeba histolytica*, and *Trichomonas vaginalis*?

Answer 37

* *G.lamblia* and *T.vaginalis* are **flagellates**, whereas *E.histolytica* is an **amoeba**. * They all have a **worldwide** distribution. * *G.lamblia* and *E.histolytica* exists as **trophozoites** _and_ **cysts**, whereas *T.vaginalis* only exists _only_ as a **trophozoite**. * *G.lamblia* and *E.histolytica* are transmitted through the **faecal-oral** route, whereas *T.vaginalis* is transmitted through **sexual intercourse**. * All can be treated with **metronidazole**.