1. Intestinal Protozoa

2. Lecture Objectives
By the end of this lecture the student is expected to be able to:
Know morphology of cysts and trophozoits and life cycle of Giardia lamblia
Discuss the clinical picture of Giardia parasites (Typical and Atypical), and trophozoits in tissue sections
Know diagnose and treatment of Giardia
Know general features of Intestinal Entamoebae and six types of Entamoebae.
Compare between E. histolytica and E. dispar.
Describe Life cycle, Pathology (intestinal and extra-intestinal).of E. histolytica
Know diagnosis and treatment of Amoebae
Life cycle of Cryptosporidium and diagnosis.

5. Intestinal protozoa General features
Protozoa colonize and infect the oro-pharynx, duodenum and colon.
The organisms are transmitted by the fecal-oral route (food/water)
3. Outbreaks of diarrhea and dysentery are especially problematic in
daycare centers.
4. The cyst forms of protozoa are resistant to chlorine and ozone and
can become important when the municipal water supply is
overburdened with these organisms—esp. farming communities

6. 1- Giardia lamblia cause :Giardiasis
Giardia lamblia is a protozoan parasite capable of causing sporadic or epidemic diarrheal illness.
Giardiasis is an important cause of waterborne and foodborne disease, daycare center outbreaks, and illness in international travelers.
Giardiasis is especially common in areas with poor sanitary conditions and limited water-treatment facilities,
Water is a major source of giardiasis transmission.

7. Giardia lamblia Life cycle
Infection initiated by the ingestion of infectious cysts (only 10 arerequired for infection)
2. Acid in the stomach stimulates the release of trophozoites from the cyst.
Trophozoites are released in the duodenum and jejunum
(upper part of small intestines) where they multiply by binary fission.
Trophozoites attach to the intestinal villi by means of a sucking disk.
Trophozoites can develop into cysts for survival outside of the host.
Trophozoites cause an explosive diarrhea such that cysts are released
into the environment.
Trophozoites remain in the G-I tract and almost never found elsewhere in the body.
Giardia lamblia trophozoite
Giardia lamblia cyst

9. Giardia lamblia Pathogenesis
The minimum infective dose for humans is estimated to be 10 to 25 cysts
Gastric acid stimulates excystation, with release of trophozoites in the duodenum and jejunum, where it multiply by binary fission
Trophozoites can attach to intestinal villi by a prominent ventral sucking disk.
The tips of the villi may appear flattened and inflammation of the mucosa with hyperplasia of lymphoid follicles may be observed
Tissue necrosis does not occur.
In addition, metastatic spread of disease beyond the gastrointestinal tract is very rare.

10. Epidemiology
The organism is found worldwide; about 5% of stool specimens in the United
Approximately half of those infected are asymptomatic carriers who continue to excrete the cysts for years
In addition to being endemic, giardiasis occurs in outbreaks related to
Contaminated water supplies because chlorination does not kill the cysts but by filtration
Many species of mammals act as the reservoirs. They pass cysts in the stool, which then contaminates water sources
The incidence is high among children in day care centers and among patients in mental hospitals

11. Giardia lamblia Clinical Manifestation
It is mainly asymptomatic in approximately 50% of infected human occurs in both children and adults
Asymptomatic cyst shedding can last six months or more.
If symptoms occur will be as diarrhea, malaise, abdominal cramps, flatulence, weight loss & vomiting.
The onset of disease is sudden and consists of foul-smelling watery diarrhea.
Symptomatic Infections:
Typical picture: Infection period 1-2 wks followed by diarrhea, vomiting & flatulence for about 6 wks,
Atypical: Severe diarrhea, malabsorption (especially in children) and cholecystitis

13. Giardia lamblia Diagnosis & Treatment
1. Stools examination :
Microscopy for cysts or trophozoits
2. Antigen detection tests.   
3. Examination of duodenal contents:
look for trophozoites.
Treatment:
Drug of choice is Metronidazole
Crypto-Gardia : Ag detection test in stools

14. Giardia lamblia Clinical Case Drug-Resistant Giardiasis
Abboud and colleagues (Clin Infect Dis 32:1792–1794, 2001) described a case of metronidazole- and albendazole-resistant giardiasis that was successfully treated with nitazoxanide.
The patient was a 32-year-old homosexual man with acquired immunodeficiency syndrome who was admitted to the hospital because of intractable diarrhea.
Examination of stool revealed the presence of numerous cysts of Giardia lamblia.
 The patient was treated unsuccessfully five times with metronidazole and albendazole without improvement in diarrhea or cyst shedding. Although combined antiretroviral therapy was also administered, it was ineffective, and viral genotypic analysis found mutations associated with high resistance to most antiretroviral drugs.
The patient was subsequently treated for giardiasis with nitazoxanide, which resulted in resolution of the diarrhea and negative results of tests for stool cyst shedding. Resistance of the infecting strain of G. lamblia to both metronidazole and albendazole was confirmed by in vivo and in vitro studies.
Nitazoxanide may be considered a useful alternative therapy for resistant giardiasis.

15. 2- Intestinal Amoebae
There are a number of intestinal commensal amoebae , the only pathogenic species is Entamoeba histolytica .
There are 6 species of Entamoeba: E.histolytica ; E.dispar; E.hartmanni ;E.coli E.gingivalis ; E.polecki.

16. E. histolytica Life Cycle
Ingestion of cysts.
2. Passage of cysts through the stomach where gastric acid stimulates the
release of the infectious trophozoites from the cysts.
Trophozoites move to the duodenum where they divide.
Trophozoites travels to the colon where they attach to colonic epithelial cells.
5. After attachment they produce a cytotoxin that kills epithelial cells so they
can gain access to deeper tissues.
Continue to divide in colon where amoeba/cysts are excreted in stool OR
Trophozoites invade the deeper mucousa and enter the peritoneal cavity
8. Trophozoites are carried in the circulation to the liver but can also be
carried to the lungs, brain and heart

17. Trophozoite stage .
Cyst: infective stage. Resist to the harsh conditions of the environment

18. E. histolytica Pathogenesis
The ingested cysts differentiate into trophozoites in the ileum but tend to colonize the cecum and colon.
The trophozoites invade the colonic epithelium and secrete enzymes that cause
localized necrosis
As the lesion reaches the muscularis layer, a typical “flask-shaped” ulcer forms that can undermine and destroy large areas of the intestinal epithelium
Progression into the submucosa leads to invasion of the portal circulation by the trophozoites
Site of systemic disease is the liver, where abscesses containing
trophozoites form.

19. E. histolytica Clinical Manifestation
Mode of infection:
Water, food
Flies can act as vector.
Can be sexually transmitted person -to -person contacts(homosexual)
Not a zoonosis.
Intestinal:
Amoebic dysentery:
is dysentery is diarrhea with visible blood and mucus in stools .
Related to the destruction of the colonic epithelial cells by the organism.
Remarkable and unique ability to produce enzymes that lyse host tissues.
Flask shaped ulcerations of the intestinal mucousa with inflammation
Secondary bacterial infection
Symptoms: abdominal pain, cramping passage of numerous watery
and bloody stools.
If untreated patients can die of dehydration.

20. E. histolytica Life Cycle
Extra-intestinal :
Amoeba can invade deeper tissues and enter the blood circulatory
system where they especially infect the liver as trophozoites are re-
moved from blood as they enter the liver.
Abscess formation in the liver is common. Also, lung, brain abscess.
Pain in the liver and elevation of the diaphragm.

21. Intestinal amoebiasis
E. Histolytica in mucosa.
Numerous trophozoites can be seen with ingested erythrocytes
Histopathology of a typical flask-shaped
ulcer of intestinal amebiasis

22. Extra-Intestinal amoebiasis

23. Gross pathology of liver containing amebic abscess

24. An amoebic Liver Abscess being Aspirated
Note the reddish
brown colour of
the pus . This
colour is due to the
breakdown of liver
cells.

25. E. histolytica Diagnosis & treatment of Amoebiasis
Intestinal:
 Stools :
microscopy,
Wet mount ( cysts and trophozoites)
Concentration methods ( only cysts)
antigen detection,
molecular methods — Detection of parasitic DNA or RNA in feces via probes can also be used to diagnose amebic infection and to differentiate between the different strains.
Serology ( mainly for invasive infections): IHA , ELISA.
Colonoscopy with biopsy and histological examination .
Extra-intestinal:
Serology: IHA , ELISA
Surgical aspirate ( needle aspiration not done as a diagnostic procedure
due to risk of extension),to look for trophozoite.
Treatment:
Metronidazole—penetrates deeper tissues and destroys amoeba present
in liver, brain, lungs etc

26. Clinical Case
A 30-year-old male experienced diarrhea for two weeks with fever of 39° C, nausea, vomiting, malaise and right upper abdominal pain.
Physical examination revealed hepatomegaly 6 cm below the right costal margin. CT scan showed a single hypodense mass in the rigth lobe of 7.8 x 5.2 cm, round, with well defined borders.
Serology was positive for Enamoeba histolytica
Amebic liver abscess was diagnosed.

27. 3- Cryptosporidium parvum
 Cryptosporidium is an intracellular protozoan parasite that is associated with self-limited diarrhea in immunocompetent hosts and severe debilitating diarrhea with weight loss and malabsorption in HIV-infected patient.  
The diagnosis of cryptosporidiosis is generally based upon microscopy since Cryptosporidium species cannot be cultivated in vitro.
Transmission of cryptosporidiosis occurs via spread from an infected person or animal, or from a fecally contaminated environment, such as a food or water source.

29. Cryptosporidium parvum Clinical manifestation
• In Immunocompetent
- Mild self-limiting enterocolitis
with:
watery bloodless diarrhea,
abdominal pain,
nausea,
vomiting,
and fever
• In Immunocompromised
– 50 or more stools per day
– Dehydration (fatigue,
abdominal cramping, and nausea)
– Common in AIDS patients

30. Cryptosporidium parvum Diagnosis & treatment
Microscopy,
Ag detection in stools.
Treatment:
Self-limited in immunocompetent patients
In AIDS patients : Paromomycin
Cryptosporidium , acid-fast stain
Crypto-Gardia : Ag detection test in stools

31. References
Murray P, Rosenthal K, Pfaller M, (2013). Medical Microbiology: Study smart with Student Consult. 7th ed.Elsevier. Chapters : 73.
Levinson WE (2010). Review of Medical Microbiology and Immunology. Eleventh-Edition, McGraw-Hill Publisher, UK. Chapters: 51
John DT, Petri Jr (2006). Markell and Voge‟s Medical Parasitology. Ninth Edition. Elsevier, UK. Chapters: 3.