1. Parasitic and Viral Infections of Gastrointestinal Tract

2. Parasitic diseases of the GIT:
Protozoa infections:
Entamoeba histolytica
Giardia intestinalis
Sporozoa: Cryptosporidium species, Cyclospora species and Isospora belli
Balantidium coli.
Helminthic infections:
Ascaris lumbricoides
Trichuris trichiura
Ancylostoma duodenale and Necator americanus
Strongyloides stercoralis

3. Amebiasis: Entamoeba histolytica (Rhizopoda).
Protozoa infections:
Amebiasis: Entamoeba histolytica (Rhizopoda).
World wide distributed, more often in the tropical countries with poor sanitary conditions→ most common cause of diarrhea among adult.
Morphology:
Trophozoite (diagnostic in invasive diseases):
The active-moving form with pseudopodia;
Invasive form so Erythrophagocytosis.
Cyst: The infective stage.
Inactive non-motile spherical form.
Immature cyst (1 - 2 nuclei): glycogen vacuole & chromatid body. Mature cyst (4 nuclei):No inclusions.

5. Asymptomatic cyst passer. Mode of Transmission: Fecal oral:
Reservoir:
Infected humans.
Asymptomatic cyst passer.
Mode of Transmission:
Fecal oral:
Ingestion of contaminated food or water
Autoinfection.

6. Life cycle of E. histolytica:N

7. Pathogenesis and virulence factors:
Colonization of epithelial cells of colon.
Contact-dependent killing; insertion of pore-forming proteins.
Ingestion of host-killed cells by phagocytosis.
Erode blood vessels and ingest RBCs for nutrition (erythrophagocytosis).
Ameba produce a cysteine proteinase that digests IgG, secretory IgA, and humoral immunity proteins.
Highly pathogenic strains kill neutrophils and APC.
Patients who use steroids tend to have disseminated infection.

8. Clinical presentation: Intestinal amoebiasis:
Acute invasive colitis; flask-shaped ulcers: dysentery; bloody mucoid diarrhea.
Chronic infection Due to repeated infection or insufficient treatment; inflammation results in granuloma formation or fibrosis with scar formation (later).
Extra intestinal Amoebiasis:
Amoebic liver abscess, pleuro-pulmonary amebiasis, amoebic abscess of the brain.
Treatment: Metronidazole. N

10. Giardiasis: Giardia intestinalis (G. lamblia).
Distribution: Worldwide.
Habitat: Small intestine especially in duodenum.
Disease: Fatty diarrhea especially in children.
Morphology:
Trophozoite active motile form (flagella), has fixation organelles (ventral sucking disk), multiply asexually by binary fission.
Cyst is the infective stage: (resist chlorine; waterborne outbreaks)
Mode of transmission:
Fecal-oral route: Children and food handlers.
Waterborne. N

12. Life cycle of Giardia lamblia:N
Life cycle of Giardia lamblia:

13. Gastric acid: ex-cystation.
Pathogenesis:
Gastric acid: ex-cystation.
Trophozoite attach to duodenum and jejunum mucosa by ventral sucking disk and start to reproduce by binary fission.
interfere with absorption and secretion (especially in heavy infection); disturbance of digestion, fatty diarrhea, lactose intolerance. non-invasive enteritis.
Trophozoite may migrate to bile duct resulting in infection of gallbladder: cholangitis and cholecystitis. n

14. All are obligate intracellular parasites.
Sporozoa
Cyclospora.
Isospora belli.
Cryptosporidium.
All are obligate intracellular parasites. N
Cryptosporidium oocyst
stained by
modified acid-fast stain.

15. Cryptosporidiosis: Cryptosporidium species
Zoonotic disease in veterinary and animal handlers.
Mode of transmission:
Fecal-oral route: poor personal hygiene.
Direct contact with infected animals.
Waterborne: swimming pool water; (the microbe resist chlorination).
The infectious oocyst reach the microvilli of small intestine where they multiply at the apical end of epithelial cells, merozoites are released and infect other cells; watery diarrheal illness (not invasive).
Diagnosis: Detection of acid-fast oocyst in stool or antigen detection. n

16. n n

17. Balantidial dysentery: Balantidium coli.
Classification: Ciliophora.
Habitat: Large intestine of man.
Reservoir host: Pigs (Commensal).
Morphology: Trophozoite and cyst form.
Multiplication and reproduction:
Simple binary fission; (asexual).
Conjugation; (sexual)
Pathogenesis: Invasive colitis due to colonization of mucosa with bloody-mucoid diarrhea. n

18. Balantidium coli cycle and diagnosis:

19. Helminthic Infections of GIT

20. Trematodes (flukes): Schistosoma. Cestodes: Taenia (tape worms).
Helminthes:
Helminthes can be classified into the following:
Platyhelminthes: flat worms.
Trematodes (flukes): Schistosoma.
Cestodes: Taenia (tape worms).
Nematodes: cylindrical worms.
Ascaris lumbricoides.
Trichcephalus trichiuris.
Ancylostoma duodenale & Necator americanus (hookworms)
Strongyloides stercoralis.

21. Nematodes (soil transmitted helminths)
Nematodes are classified into two groups according to rout of infection:
Infection acquired by swallowing the infective eggs.
Ascaris lumbricoides ; (large roundworm), and Trichuris trichiura ; (whipworm)
Skin penetration by infective larvae: Ancylostoma duodenale and Necator americanus ; (hookworms), and Strongyloides stercoralis All then show a systemic migration through the lungs to the intestine.
All inhabit the small bowel except Trichuris (large intestine).

22. Ascaris lumbricoides :
Distribution: worldwide
Habitat: Free in small intestine.
Definitive host: Man, no intermediate host (direct life cycle).
Morphology: Whitish yellow cylindrical worms: Male cm x 3 mm with posterior curved end Female cm x 5mm with tapering end. Female lay 200X103 eggs per day.
Infective stage: fertile (embryonated) eggs.

24. Life cycle of Ascaris lumbricoides :N

26. Clinical presentation: Usually asymptomatic.
Pulmonary symptoms: cough, sputum production.
Intestinal symptoms: abdominal pain, nausea, vomiting, and indigestion.
Complications:
Light infection: Obstruction of bile duct (jaundice), pancreatic duct (pancreatitis), & appendix (appendicitis) Peritonitis may established due to larval or adult worms penetration to the abdominal cavity.
Heavy infection: Intestinal obstruction and bronchopneumonia. N

28. Trichocephalus trichiura infection:(Whipworm):
-Site of inhabitation: Cecum
-Infective stage: Embryonated ova.
-Mode of transmission: passively swallowed by the mouth from contaminated hands or food;
-Life Cycle:
Without intermediate host and reservoir host (direct life cycle).
Ova are passed in the stool and after 3 weeks they become infective When ingested, embryonated ova hatch in small intestine releasing larvae which invade the mucosa and after 3-10 days it mature to adult worms which return to the lumen and start to produce eggs.
-The life span of the adult is about 3-5years.

29. Life cycle of Trichocephalus trichiura :N

31. Hookworms infection: Ancylostoma duodenale and Necator americanus
Morphology:
Adult stage:
A white or light yellowish worm (1 cm).
Female is slightly larger than male; the male’s posterior end is expanded to form a copulatory bursa.
Mouth capsule carry four teeth.
Eggs:
60×40 µm in size, oval in shape with 2-8 cells.

35. Pathogenesis and tissue damage:
Filariform larvae (infective stage) penetrate the skin.
Local manifestation of itching and irritation (Ground itch).
The larvae enter the circulation through the bloodstream or lymphatics, transferred to right side of the heart and then the lungs.
In the lung; mature larvae break the alveolar wall and enter the alveolar lumen.
Coughed up and swallowed into GIT where it grow to adult stage and produce eggs in the stool. N

36. The effect of adult worms on human:
Destruction of intestinal mucosa by it’s teeth; complicated by bacterial enteritis ; Inflammation.
The parasite secrete anticoagulants; that inhibit blood clotting; sucking of host’s blood, chronic anemia.
Treatment:
-Almost all nematodes infections of GIT are treated by: mebendazole, Albendazole, or thiabendazole. n

37. Strongyloides stercoralis infection:
Habitat: Free living, humans and animals.
Life cycle: similar to hookworm cycle.
Direct skin penetration by filariform larvae.
Female worm invade the bowel wall to release its eggs that hatch to produce rhabditiform larvae which are passed in the stool.
Symptoms: abdominal pain, vomiting and diarrhea.
Complications:
Rhabditiform larvae can cross to the peritoneum causing bacterial peritonitis.
Autoinfection in all patients and hyperinfection syndrome in immunocompromised patients.

38. Rhabditiform Larvae; (diagnostic) Filariform Larvae;(infective)

39. Viral Gastroenteritis

40. Viral gastroenteritis ranges from a self-limited watery diarrhea (nausea, vomiting, fever) to severe dehydration, hospitalization and even death.
Clinically, viral gastroenteritis can be grouped to:
Sporadic cases:
In infants: The leading cause is rotavirus (the commonest), followed by adenoviruses 40 & 41.
In adults: Caused by caliciviruses (the commonest), rotavirus, astroviruses and adenoviruses.
Epidemic gastroenteritis:The leading cause of outbreaks is Norwalk virus.

41. From Latin rota means “wheel“.
Rotavirus:
From Latin rota means “wheel“.
-Reoviridae family [Respiratory& Enteric Orphan].
Virology: Virions are icosahedral, non-enveloped with double shelled capsid. Ds RNA with 11 segments.
RNA-dependent RNA polymerase; (human cells do not have RNA polymerase that can synthesize mRNA from double-stranded RNA template).
7 groups [A-G]:- Group A is the most common.
Transmission: Contaminated food or water.
Peak: Winter. mortality is high in developing countries.
Orphan: not associated diseases.

43. Incubation period: 1 to 3 days (short)
Duration of illness: 2-6 days (self limited).
Pathogenesis:
Attached and replicate in small intestinal villi and causes structural changes in villi (villus shortening) and mononuclear infiltrates in the lamina propria.
Watery diarrhea due to:
Mal-absorption of carbohydrate and nutrients; inhibition of water reabsorption due to osmotic pressure.
Rotavirus enterotoxin NSP4 lead to activation of Ca dependent Cl secretory; loss of Cl. N
NSP= non-structural proteins.

44. - n

45. Non enveloped, icosahedral, Ds DNA genome.
Enteric Adenoviruses
Family: Adenoviridae
Non enveloped, icosahedral, Ds DNA genome.
The only virus with a fiber extending from each of the 12 vertices of the capsid Fibers: Attachment, hemagglutinin, type-specific antigen
There are 41 known antigenic serotypes Types 40 and 41 cause infantile gastroenteritis.
Watery-diarrheal illness. N

46. Norovirus (Norwalk virus):
Family: Calciviridae (Calyx =cup)
Small, naked, icosahedral capsid and positive sense Ss RNA.
They have cup-shaped depressions on their capsid surface, giving the virion a “Star of David” appearance.
Previously named Norwalk virus for an outbreak in school in Norwalk, Ohio in 1969.
About half of the outbreaks of acute infectious nonbacterial gastroenteritis are due to Norwalk virus. N

47. Astrovirus Family: Astroviridae [astro= a star]
Linear, icosahedral capsid and positive sense Ss RNA.
The surface of the viral particle has five or six-pointed star appearance.
Has 8 serotypes.
-Transmission: contaminated food or water. Causes sporadic gastroenteritis in infants, children, elderly and immunocompromised patients.
-Diagnosis: ELISA or electron microscopy. N

48. Caliciviruses
Astroviruses