Assistant Professor Dr.
Syed Yousaf Kazmi

• Major Parasites that cause GIT disease, their epidemiology, etiology, life cycle and pathogenesis
• Mechanism of transmission. Enlist clinical conditions
• Discuss the laboratory diagnosis of these infections

• Parasites are Eukaryotes
• Two major groups
– Protozoa (unicellular)
– Metozoa/Helminth (Multicellular)- worms
• Trophozoite -trophē=nourishment, zōon=animal
(active feeding stage of a protozoal parasite)
• Cyst/ oocyst -inactive and infective form
• Protozoa-motility via pseudopods, flagella, cilia etc

INTRODUCTION TO BASIC PARASITOLOGY
• Helminths-worms
• Definitive host-which harbor sexual phase of parasite
• Intermediate host-which harbor asexual phase of parasite

PROTOZOA
Entamoeba histolytica
Giardia lamblia
Cryptosporidium parvum
HELMINTHS
Hookworms(Ankylostoma duodenale,
Necator americanis)
Ascaris lumbricoides
Strongyloides stercoralis
Tinea saginata, Tinea solium
Hymenolepsis nana
Trichuris trichiura
Diphylobothrium latum

• Worldwide-common infection
• Trophozoites attach large gut
• Flask shape ulcers
• Mucus, epith cells, pus cells, amoeba pass in stool
• Acute-Extreme abd tenderness, dysentery, dehydration, incapacitation
• Subacute-Diarrhea, abd cramps, vomiting, desire to defecate, weight loss, general malaise
• Asymptomatic cyst passers
E histolytica/dispar trophozoites
E histolytic/dispar cyst

• Feco-oral route
• Poor sanitation & hygiene
• Cyst ingestedcontaminated water, veg, fruits, flies

• Common pathogen of duodenum & jejunum
• Trophozoite heart shaped sucking disc-attachment to villi
• Does not invade, but attachment cause irritation, inflammation of duodenum/ jejunum
• Crypt hypertrophy, villous atrophy/ flattening, epith cell damage
Giardia lamblia trophozoite
Giardia lamblia cyst

• Asymptomatic- if light infection
• Acute/ chronic diarrhea- in heavy infection
• Stool bulky, watery, semisolid, greasy, foul smelling- Mal-absorption
• Fatigue, weakness, weight loss, abd cramps, distention, flatulence-long period
• Symptoms intermittent in many cases
• Nutritional def e.g. iron def, folate def etc

• Ingestion of cyst contaminated water, food
• Direct fecal oral route
• Cysts can survive for 3 months
• Drinking stream water during camping

• Protozoa of small intestine
• Immuno-compromised e.g.
HIV inf- serious life threatening diarrhea
• Pathogen of rodents, monkeys, cattle, etc.
• Unrecognized cause of self limiting diarrhea in healthy
• Oocyst infective form
• Contaminated food/ water source of infection
• High vol stool like cholera
Oocysts of C parvum modified ZN stain

• Oocysts- excystation of sporozoites-infect epith cellsreleased-infect other epith cells
• Whole life cycle within host
• Incubation period 1-12 d
• Diarrhea-large volume stool
• Cholera like pic in HIV, severe dehydration, shock and death
• Self limiting diarrhea in healthy
Life cycle of C parvum

• Large worm,
♂&♀
• Ingestion of eggs
• Larva hatch, heart lung cycle, reenters intestinemature into adults
• Eggs passed in stool
• Eggs infective after 1 month till many months
• Very common world wide
• Poor sanitation & hygiene

• Pathogenesis is due to larval migration in lungirritation, mucus production, wheeze
(Loeffler’s syndrome)
• Adults-mechanical obstruction of gut, appendicitis, pancreatitis,
• Abdominal pain, vomiting,
• Anemia

• Ankylostoma duodenale,
Necator americanus
• Small 10 mm,
♂
&
♀
• Female release up to 10,000 eggs/day
• Larva hatch in day or two, survive for several weeks in moist environment
• Penetrate intact skin of barefoot person, enter blood and undergoes heart lung cycle like
Ascaris
• Adult reach intestine and attach to small intestine mucosa

• Adult worm attach intestinal villi-buccal teeth
• Secrete anticoagulant and feed on blood
• Few hundred worms – blood loss and anemia
• Abdominal discomfort, diarrheoa,
• Ground itch
Adult hookworm
Ground itch

• Adult
♀
2mm- parthenogenic
• Eggs passed in feces, larva develop into either infective or free living form
• Infective larva penetrate skin, heart lung cycle like Ascaris
• Adult form reach intestine
• In immuno-compromisedserious fulminant hyperinfection
• Severe diarrhea, abd pain, GI bleeding, nausea, vomiting
• Wheezing, hemoptysis, cough
• Chronic infection-many years
Adult Strongyloides stercoralis with larva

• Humans eat "measly beef" or
"measly pork" containing the bladder-like larvae called cysticerci- inf of T saginata and T solium, respectively
• Cysticerci develop in to adultintestine
• May reach many meters
• Few problems, most asymptomatic
• Diarrhea and abdominal pain
• Egg-filled terminal segments break off-pass out with human feces-infective for cattle/pigs

• Female pinworms about 10 mm in length
• Worldwide, mostly children
• perianal pruritus, especially at night
• female worms migrate down from the colon at night & lays egg-severe itch
• Scratching the anal region promotes transmission
• eggs are highly infectious within hours of being laid (hand-tomouth transmission
• Irritability and fatigue from loss of sleep
Ova of Enterobius vermicularis

• Fish tapeworm
• Enormous size, sometimes exceeding 10 m in length
• Eat improperly cooked or raw fish that is infected with the infective larvae known as plerocercoids
• Worm > 1 million eggs per day released
• Vague abdominal discomfort and loss of appetite
• Unusual capacity to absorb vitamin B
12
-deficiency leading to anemia

• Dwarf tapeworm of humans
• Worldwide & one of the most common tapeworm infections in humans
• Direct human to human cycle
• Autoinfection common
• Massive infections, mostly in children
• Abdominal discomfort
• Most infections are asymptomatic
Hymenolepsis nana ovum

1. STOOL MICROSCOPY
– Most important and very cheap method of diagnosing parasitic infestation of GIT
A. Naked eye examination-worm in stool e.g. Ascaris lumbricoides, Taenia saginata/solium etc. Blood, mucus in dysentery
B. Wet film examination-motile trophozoites and cysts of
Giardia lamblia, Entamoeba histolytica, RBCs, WBCs, ovum of hookworm, Ascaris , Taenia spp, etc
C. Iodine stained examination-better visualization of cysts of Giardia, Entamoeba
D. Modified ZN stain- Oocysts of Cryptosporidium

Tapeworm Hookworm ovum
Taenia ovum
E histolytica/dispar trophozoite
Giradia lamblia trophozoite
Ascaris ovum

LAB DIAGNOSIS OF PARASITIC INFESTATION
OF GIT
• Upper GI Endoscopy
• Biopsy examination for Giardia,
Cryptosporidium
• “Scotch tape” test for Enterobius vermicularis ovum
• Serological Tests ELISA for Giardia lamblia,
Entamoeba histolytica etc. antigen detection