Protozoan And Helminthic Infections Of The GIT

Question 1

Giardia Lamblia: Pathogenesis?

Answer 1

• Attaches to wall of upper small intestine via ventral “sucker”.
• Causes villous atrophy (cleaved off) > malabsorption
• Cysts can remain viable in environment for 24-48 days.
• Can gain access to biliary system and reside in the bile duct.

Question 2

Giardia Lamblia:Life Cycle?

Answer 2

• Trophozoite - flagellated, binucleated. Adheres to brush border of upper small intestine. Contractile forces involved, blunts villi.
• Cyst - resistant wall, formed in large intestine, passes out in faeces.

Question 3

Giardia Lamblia: Diagnosis?

Answer 3

• 3 stool samples
• Antigen detection assays (ELISA)

Underdiagnosed as selection criteria is outdated. Misconception that it is only picked up after travel.

Question 4

Giardia Lamblia: Clinical presentation?

Answer 4

• Self-limiting diarrhoea - can be chronic in immunocompromised.
• Can be asymptomatic
• if diarrhoea present - usually foul smelling, fatty stool.
• Cobblestone effect - on microscopy - each bump is a trophozoite, no villi as sheered off.

Question 5

Cryptosporidium Parvum: Pathogenesis?

Answer 5

-Transient non-bloody diarrhoea
-Hygiene is most effective way to combat
-Durable oocyst
Treatment for rehydration is used to treat. Fluid rehydration, elctrolyte replacement , management of pain. Nitozoxane drug used for immunocompromised.
-Minimally invasive mucosal pathogen as it invades surface epithelial cell lining of intestinal tract but not deeper. Marked mucosal inflammation.

Question 6

Cryptosporidium Parvum: Diagnosis?

Answer 6

Microscopy of stool samples: acid fast, fluorescent antibodies, ELISA, PCR.
-Underdiagnosed.

Question 7

Crytosporidium Parvum: Life Cycle?

Answer 7

• Oocyst - in water - spore-related, resistant to chlorine treatment, pools can be place of infestation, could also be respiratory transmission as well as ingestion.
• Sporozoites (in intestine) - epithelial lining. Asexual reproduction.
• Macrogamontes (female)/ Microgamontes (male)
• Oocyst - thick oocysts will exit in faeces, thin oocysts stay in causing autoinfection and cycle of disease.

Question 8

Cryptosporidium Parvum: Clinical presentation?

Answer 8

• signs and symptoms usually appear after approx. a week of infection - watery diarrhoea, dehydration, lack of appetite, weight loss, stomach cramps or pain, fever, nausea, vomiting.
• Symptom last between two weeks and a month
• can be asymptomatic.

Question 9

Entamoeba Histolytica: clinical manifestation?

Answer 9

• small superficial ulcers - mild diarrhoea
• severe ulceration of colonic mucosa > amoebic dysentry
• trophozoites may spread to liver > abscesses
• overlying skin may also be affected by abscesses (very rare).

Question 10

Entamoeba Histolytica: pathogenesis?

Answer 10

-Most people affected are asymptomatic. Immunocompromised increases susceptibility of host.
- Cysts ingested undergo excystation in terminal ileum.
-Adhere to epithelial cells of large intestine using lectin component.
-Enzymatic penetration into blood vessels by breaking walls of capillaries. (Rarely) spreads hematogenously to distal organs e.g. liver.
-Trophozoites ‘feed’ off these lysed cells > bloody diarrhoea.
-Resistant cysts pass out in stool (can re-infect in cases of contamination).
-

Question 11

What are the 3 classifications of Helminth?

Answer 11

• Nematodes (roundworms)
• Cestodes (tapeworms)
• Trematodes (flukes)

Question 12

Nematodes

Answer 12

• clinically most important helminth
• transmission often through soil, swallowing infective eggs or larval skin penetration/systemic migration through lung to intestine (autoinfection).
• diagnosis - stool microscopy

Question 13

Taenia Solium

Answer 13

• Tapeworm/Cestode
• can get from undercooked pork and eggs
• lives in large intestine - has a scolex (anterior suckers/hooks) for attachment.
• length up to 7m
• Usually causes vague GI symptoms: abdo pain, cramps, nausea, diarrhoea, weight loss

Question 14

Strongyloides Stercoralis

Answer 14

• disrupts intestinal mucosa > villus atrophy
• autoinfection - small intestine larvae will invade the intestinal mucosa of the colon or skin of the perianal region > enter circulation > lungs > small intestine (cycle repeats).
• Persists for years.
• Clinical presentation - diarrhoea (persistent if immunocompromised), malabsorption, anal pruritis, dehydration.

Question 15

Trichiuris Trichiura

Answer 15

• Acquired through ingesting eggs (classically on leafy veg)
• Commonly referred to as whipworm
• Manifests as asymptomatic (if mild infection), abdo pain, nausea, bloody diarrhoea, retal prolapse can occur.

Question 16

Ascaris Lumbricoides

Answer 16

• Commonly ‘giant roundworm’
• 13-35cm long
• Highest risk to those in countries with poor sanitation
• Eating unwashed fruit and veg is also a risk factor.
• Clinical manifestation - small number are asymptomatic, allergic reaction (high IgE), intestinal obstruction, malnutrition (particularly proteins as they feed on them, can stunt growth of children), can be expelled from mouth and nose, Loffler’s syndrome (pulmonary eosinophilia - cough, dyspnoea, wheezing, pain, nausea, bloating, vomiting, anorexia, and intermittent diarrhoea).

Question 17

Enterobius Vermicularis

Answer 17

• small nematodes (~1cm)
• females migrate at night to anus to lay 1000s of eggs
• can reach infective stage within hours
• intense itching and inflammation, diarrhoea, eosinophilia

Question 18

Ancyclostoma Duodenale

Answer 18

• Hookworm
• Larvae penetrates skin (most commonly through soles of feet) > enters bloodstream > migrates to gut (via lungs).
• Attaches to small intestine where females lay eggs.
• Causes iron deficiency anaemia - 0.03ml loss per day per worm