22. Protozoa (Giardia) Flashcards
what are the 3 names for the species of giardia that infects humans?
lamblia, intestinalis, duodenalis
T/F giardia is the most common enteropathogen world wide, but is not necessarily a fatal infectious agent
true
in which climate is Giardia most common?
in warm climates
is Giardia flagellated?
yes
where in the body does giardia infect?
the duodenum and intestine
the infection of giardia ranges from ________ colonization to _____ or ______ diarrhea and malabsorption
asymptomatic acute chronic
is Giardia more prevalent in adults or children?
children
T/F Giardia is the most common intestinal flagellate of humans
true
in which type of locations is Giardia often found?
in streams, lakes, mountain resorts
which animals perpetuate the infectious cycle? (reservoir)
reservoir animals include beavers and muskrats
how does one get infected by Giardia?
by ingesting the cycts
how many cysts are needed for infection by Giardia?
only 10
approximately how many humans are asymptomatic? why is this bad?
50% - they are important carriers of disease
how can giardiasis be acquired?
- through the consumption of inadequately treated water
- ingestion of uncooked fruits and vegetables and fruits (that were washed in contaminated water)
- person to person spread
what is needed in municipal treatment plants that would remove the parasite?
filtration AND chemicals
who is the main reservoir of Giardia
humans
what is the importance of animal reservoirs?
it is unclear
where are the non-zoonotic Giardia found?
- rodents
- birds
- reptiles
- amphibians
what is the Rodent Giardia?
G. muris
what is the amphobian Giardia?
G. agilis
what is the Great Blue Heron Giardia?
G. ardae
what is the Voles Giardia?
G. microti
who was the first scientist to use a microscope to observe bacteria, sperm and blood cells, protists (free living and parasitic)
van Leeuwenhoek, the father of microbiology
what did van Leeuwenhoek observe particularly to do with parasites?
Giardia in his own stool
what are the two life stages of Giardia?
- trophozoites
- cysts
in what part of the intestine are the trophozoites found?
in the upper 1/3 of the small intestine
what happens to the trophozoites when they get swept into the colon?
they encyst
what is shed in feces?
trophozoites and cysts, the trophozoites degrade quickly
what is the persistent environmental form?
the cysts
what is the morphology of the trophozoite?
- heart/pear shaped
- symmetric
- large concave disk on the anterior ventral surface
- 4 pairs of flagella originating from the basal bodies located near the nucleus
- median bodies, which are unique to the Giardia cell
- presence of other organelles
- viruses and bacteria are found in the cytoplasm as endosymbionts
what is unusual about the morphology of Giardia`?
- 2 nuclei with central karyosomes
- Absence of functional mitochondria
- Altered Golgi apparatus
- Ventral disk
- Median body
how does the trophozoite adhere?
via the adhesive disk
what is the ventral disk made of?
- complex of microtubules and fibrous structures and serve as organelles of attachment
- the structure is rich in tubulin, giardin
where does the trophozoite live in the host?
in the upper part of the small intestine (duodenum, jejunum and upper ileum)
what do the trophozoites do in the upper small intestine?
- attaches to the epithelial cells
- feeds on mucous that forms in response to irritation
- absorbs vitamins and amino acids
why is it a problem that Giardia is in the intestine?
- interferes with absorption in the host, especially lipids
- can interfere with vitamin/nutrient absorption
- vit A -> vision
- vit D -> rickets
(both due to long standing infections)
what is the morphology of the cyst?
- ovoid in shape
- four nuclei present, often concentrated at an end
- flagella shorten and are retracted within the cyst
- axonemes provide internal support
how many nuclei are present within the cyst?
4
what is the mechanism of the flagella?
they shorten and are retracted within the cyst
what are axonemes?
they provide internal support
what is the cyst wall composed of?
fibrous components containing polymers of galactosamine and proteins
when does the cyst form?
as trophozoites become dehydrated when they pass through the large intestine
how long can cysts remain viable in the external environment (water)?
for a couple of months
are the cysts resistant to chlorine?
yes
how many cysts can be passed in one stool sample?
14 billion
what amount of cysts constitutes a moderate infection?
300 million
how can cysts be transmitted?
- direct transmission (person to person)
- formites: contaminated water or food
what do ingested cysts release in the host?
trophozoites
what are the best conditions for cyst survival?
cool, moist
how many months can cysts stay viable in different cold-water temperatures?
two months at 8°C
one month at 21°C
can cysts survive freezing?
yes
Giardia cysts are relatively resistant to _______ and to __________________.
chlorination
ultraviolet light radiation
how are cysts eliminated?
- Susceptible to desiccation and direct sunlight
- Boiling is effective for inactivating cysts.
- Human milk contains glycoconjugates and secretory IgA antibodies that may provide protection to nursing infants
what does acid in the stomach stimulate?
the excystation of the trophozoites
where are trophozoites released? what do they do there?
in the duodenum and jejunum and they multiply by binary fission
how do trophozoites attach to the intestinal wall?
by means of a sucking disk
why do the trophozoites cause explosive diarrhea?
as a means of spread back into the environment (was selected for)
are trophozoites ever found extra-intestinally?
almost never
what are common populations affected by Giardia?
- children
- travelers, hikers
- swimmers
what is the prevalence in different age groups in developed countries?
- 2% of adults
- 6-8% of children
- up to 15% for children in developing countries
what is the morbidity rate of naïve populations?
20%
how do infections often resolve?
spontaneously
what is the occurence of chronic infections?
less than 4%
what do chronic infections possibly contribute to?
the decreased lifespan of immunodeficient individuals
which animals are most affected?
young animals
which animals have the greatest prevalence rates?
– Puppies: 20‐35%
– Kittens: 10‐15%
– Foals: 17‐32%
– Calves: 5‐90%
– Lambs: 6‐80%
– Pigs: 7‐44%
is it life threatening to animals?
not usually
what are the two types of pathologies of giardiasis?
acute and self limiting
chronic
The infection can be __________ or the cause of a severe __________ with malabsorption
asymptomatic
enteropathy
why does absorbance decrease?
due to villus blunting
what is the characteristic pathology of giardiasis?
malabsorption
what are the clinical manifestations of Giardiasis?
- 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.
- Malabsorption of sugars, fats, and fat‐soluble vitamins has been well documented and may be responsible for substantial weight loss.
- Spontaneous recovery occurs in 2 weeks HOWEVER chronic disease with several relapses may occur.
what do the trophozoites look like in microscopy?
- “Tear drop” shape
- Two nuclei and tumbling mobility
how is diagnosis of giardiasis done?
- direct microscopic observation in feces
- immunofluorescence
- ELISA, PCR
how many stool specimens are requires to achieve a sensitivity of >90%?
3, because Giardia may appear on a given day and not be present on the
how is giardiasis treated?
- infections may be self-limiting
- anti-protozoal drugs
- consider treatment due to zoonotic potential
- chronic cases may be resistant and prolonged therapy may be necessary
how can giardiasis be prevented?
- handwashing
- water (heat, filter, chlorinate)
- food (wash raw fruits and vegs, travellers avoid uncooked foods)
what is the cyst wall composed of?
The cyst wall is composed of fibrous components containing polymers of galactosamine and proteins
when does the cyst form?
The cyst forms as trophozoites become dehydrated when they pass through the large intestine.
how many cysts can be passed in 1 stool sample?
14 billion, moderate infection 300 million
