lecture 17- protozoa, giardia and entamoeba Flashcards
what is giardia lamblia?
an intestinal protozoan parasite of vertebrates and is a significant global cause of endemic and epidemic diarrhea
giardia lamblia is the most common …
enteropathogen worldwide
what area of the body does the giardia spp infect?
the duodenum and small intestine
what group of people is giardia infection most common in?
children
where does giardia infection most commonly occur?
streams, lakes mountain resorts, reservoir animals such as beavers and muskrats perpetuate the infectious cycle
how does transmission of giardia infection occur?
ingestion of cysts through contaminated water
what are the two cycles that occur in the transmission of giardia?
the domestic cycle (domesticated animals) and the sylvatic cycle (wild animals)
how many humans are asymptomatic with giardia infection?
50%
giardiasis is acquired through
- the consumption of inadequately treated water
- ingestion of uncooked vegetables and fruits
- person-person spread
what is the main reservoir host of giardia?
humans
what are the two life stages of giardia?
trophozoite and cyst
what are cysts responsible for in the life cycle of giardia?
transmission
where can cysts and trophozoites be found
feces
what is the morphology of the trophozoite?
- heart shaped and symmetric,
- contains a large concave ventral disk on the anterior ventral surface
- has 4 pairs of flagella originating from the basal bodies located near the nucleus
- median bodies are unique to the giardia cell
- virus and bacteria found in the cytoplasm (possible endosymbionts)
why is the trophozoite an unusual eukaryote?
- 2 nuclei with central karyosomes
- absence of functional mitochondria
- altered golgi apparatus
- ventral disk
- median body
what is the trophozoite’s ventral disk made of?
- made of a complex of microtubules and fibrous structures and serve as organelles of attachment
- the structure is rich in tubulin, giardin
what is the cyst wall of giardia made of?
composed of fibrous components containing polymers of galactosamine and proteins
when does the cyst of giardia form?
when trophozoites become dehydrated when they pass through the large intestine
what are the giardia cysts resistant to?
chlorine
what happens once cysts are ingested?
they release trophozoites
what do released trophozoites do?
multiply and encyst in intestines, then excreted in feces
under what conditions do cysts survive well under?
- survive well in cool, moist conditions
- remain viable for months in cold water
- can also survive freezing
what are giardia cysts susceptible to?
- dryness and direct sunlight
- boiling
populations affected by giardia?
- children
- travelers, hikers
- swimmers
how are giardia infections resolved?
they usually resolve spontaneously
… animals are most affected by giardia
young animals, usually not life threatening
what is the pathology of giardia?
- can be acute or self limiting or chronic
- infection can be asymptomatic or the cause of a severe enteropathy with malabsorption
- absorption decreases due to villus blunting causing malabsorption
- malabsorption is the characteristic of the pathology in giardiasis
what are the characteristics of one’s stool when infected with giardia?
stools may be profuse and watery and later become greasy and foul smelling
stools do not contain….
blood, mucus, or fecal leukocytes
abnormal stool patterns may alternate with …
periods of constipation and normal bowel movements
in Giardiasis, what is the factor responsible for substantial weight loss?
malabsorption of sugars, fats, and fat-soluble vitamins
how long is it until there is spontaneous recovery of Giardiasis?
2 weeks
how is Giardiasis diagnosed?
- direct microscopy observation in feces, i.e., the cysts and trophozoites
- immunofluorescence
- ELISA, PCR
in diagnosing Giardiasis, what is required to achieve a sensitivity greater than 90%?
3 stool specimens
what is the treatment for Giardiasis?
- Anti-protozoal drugs:
- Metronidazole
- Tinidazole
- Ornidazole
What are the prevention and control measures of Giardiasis?
- handwashing
- not drinking contaminated water and treating potentially contaminated water
- wash raw fruits and vegetables
- eradicate giardia from BOTH asymptomatic carriers and diseased patients
- Campers/travelers should boil AND filter water taken from lakes and streams AND from municipal water in areas where disease is endemic
- maintain functioning filttration systems since the cysts are fairly resistant to chlorine and ozone/UV treatment
what disease does Entamoeba histolytica cause?
Amoebiasis (Amoebic dysentery)
what is the invasive form of Entamoeba?
E. histolytica
what is the non-invasive form of Entamoeba?
E. dispar
what is the distribution of Entamoeba histolytica?
worldwide distribution but is most common in the tropical and subtropical areas of the world
what is the overall prevalence of Entamoeba histolytica?
2-60%
<1% in Canada and the USA
up to 60% in the tropics
Amoebiasis is the .. parasitic cause of death worldwide, surprassed only be malaria and schistosomiasis
third leading
out of everyone infected with Entamoeba, how many of those develop the disease?
only 10%
what are the two types of infection that Entamoeba are responsible for?
- extra-intestinal
2. intestinal - mild to severe
what are the ways Entamoeba transmitted?
- direct contact of person to person (fecal-oral)
- food or drink contaminated with feces containing the E. histolytica cyst
- use of human feces (night soil) for soil fertilizer
- sexual transmission (oral-anal)
- contamination of food by flies and possible cockroaches
what populations are most affected by Entamoeba?
- all age groups are affected, but the disease is most severe in children, elderly, and pregnant women
in what environments is Entamoeba transmitted in the most?
- poor sanitation, sewage leakage
- night soil for agriculture
- seasonal variation
what are the two stages of the Entamoeba histolytica life cycle?
- Cyst: the infective stage
- Trophozoite: the vegetative stage
what are the characteristics of the E. histolytica cyst?
- resistant to the harsh conditions of the environment
- sensitive to heat and freezing; last a few months in water
- resistant to chlorine; remove via flocculation/filtration
what are the characteristics of the E. histolytica trophozoite?
- must encyst to survive in the environment. it is a fragile structure
- it is a strict anaerobe
how does infection of E. histolytica begin?
ingestion of the cyst
only 1 cyst is necessary to initiate infection, making it one of the most efficient pathogenic protozoa
how does E. histolytica replicate in the colon?
via binary fission
what is the morphology of the E. histolytica trophozoite?
- contains a spherical containing central karyosome and peripheral evenly distributed small chromatin dots
- has food vacuoles that contain leukocytes, bacteria, maybe RBCs
what are the characteristics of E. histolytica nucleus?
contained numerous pores. the inner surface membrane is lined with peripheral chromatin
what are the characteristics of E. histolytica Karyosomes?
located in the center of the nucleus. probably contains DNA
what are the characteristics of E. histolytica chromatoid bars?
seen in cysts, they are blunt rods or splinter shape. they eventually disappear as the cyst ages
what are the characteristics of the E. histolytica mitosome?
its a remnant mitochondrion, and has a double membrane, but does not have its own genome. the genes for mitosomal components are contained in the nuclear genome
what are the characteristics of the E. histolytica vacuoles?
they occupy a great proportion of the cytoplasm. they vary between 5-9um in size. They may contain cellular debris, RBCs, bacteria, or contain nothing
what are the 5 types of vacuoles of E. histolytica?
- phagocytic
- macropinocytic
- micropinocytic
- primary lysosomes
- secondary lysosomes
what does pathogenesis of E. histolytica depend on?
- parasite virulence
- host resistance
- condition of the intestinal tract
where are non-pathogenic trophozoites located in the host?
in the lumen
where are pathogenic trophozoites located in the host?
invade intestinal mucosa
what do trophozoites produce that lead to the formation of a flask-shaped ulcer?
histolytic enzymes that produce necrosis of mucosa
what are rare events that could occur due to the pathogenesis of E. histolytica?
- perforation haemorrhage
2. amoeboma
what are the common events that result due to pathogenesis of E. histolytica?
invasion of blood vessels, direct extension outside bowel, extraintestinal lesions
what are the symptoms of non-invasive/non-pathogenic E. histolytica?
non-dysenteric diarrhea, abdominal cramps, other GI symptoms
what are the symptoms of pathogenic E. histolytica?
- ulcers, dysentery
- ulcer enlargement –> peritonitis
- metastasis –> extraintestinal amoebiasis
- cessation of cyst production
what organ does extra-intestinal amoebiasis primarily affect?
the liver via the portal vein
what happens as a result of pulmonary amoebiasis?
rupture of liver abscess through diaphragm, secondary bacterial infections, fever, cough, pain
what happens as a result of cutaneous amoebiasis?
intestinal or hepatic fistula, mucosa bathed in fluids containing trophozoites which result in perianal ulcers
how is E. histolytica diagnosed?
microscopy,
immuno-fluorescence assay, PCR
infection of E. histolytica leads to long-lasting …
antibody production
what is the treatment for E. histolytica?
- asymptomatic patients are given luminal amoebicide, i.e., Diluxanide furoate (kills trophozoites and cysts in the lumen of the intestine)
- symptomatic patients are given Metronidazole, Tinidazole (tissue amoebicide) and then Diluxanide furoate (luminal amoebicide)
what are the primary and secondary prevention measures taken against E. histolytica?
Primary prevention: 1. safe fecal disposal 2. safe water supply 3. hygiene 4. health education Secondary prevention: 1. early diagnosis 2. treatment
