23 - Intro to Protozoa Flashcards
Protozoa
- Single celled organisms
- Found in every conceivable soil and water habitat
- Range from 2um to 20cm
- Contain organelles common to all eukaryotes (nuclei, cell membrane, ER, mitochondria, etc)
Direct infection
Only one host in life cycle
Indirect infection
Two or more host required
Definitive or primary host
Where parasite reaches maturity and undergoes sexual reproduction
Reservoir host
Can harbour pathogen often with minimal effect
Secondary or intermediate host
Where the parasite usually undergoes asexual reproduction
What can cause immunosupression
- Other infections (AIDS)
- Cancer
- Drug or radiotherapy (in organ transplant or cancer treatment)
- Age
- Pregnancy
Zoonotic disease
Any disease which can be transmitted to humans from animals (e.g. East African sleeping sickness, toxoplasma)
Anthroponosis disease
A disease that is spread from humans to humans (e.g. West African sleeping sickness, Malaria)
Direct transmission
Passed directly from one infected host to another by some physical means or from the environment
Food or waterborne transmission
From contaminated food or water (Fecal – oral route)
Intermediate host vs vector transmission
Distinction depends on size, speed of movement and active involvement (e.g. a pig versus a mosquito)
Examples of direct transmission
- Trichomonas vaginalis
- Naegleria fowleri
Trichomonas vaginalis
- Cosmopolitan flagellate, pathogen of trichomoniasis
- Most common STI
- Asymptomatic in men
- Inhabits female lower genital tract and male urethra and prostate
- Causes vaginitis, urethritis and prostatitis
Trichomonas vaginalis morphology
- Exists only as an ovoid trophozoite
- Four anterior flagella
- Undulating membrane attaches posterior flagellum to body
- Axostyle (a central supporting
rod) extends posteriorly - Short survival outside the body
Trichomonas vaginalis Life Cycle
- No cystic stage known
- Trophozoite reproduces by binary fission
- Infection through sexual intercourse (male carrier, females guaranteed infection)
Trichomonas vaginalis pathogenesis
- Axostyle important for attachment and irritation
- Degeneration and desquamation of vaginal epithelium followed by leucocytic inflammation
Trichomonas vaginalis clinical features
- Vaginitis resulting in frothy, creamy white discharge
- Vulva and cervix inflammation
- Male may be asymptomatic or latent with recurring urethritis
- Prostatitis can occur
Trichomonas vaginalis treatment
Metronidazole
Naegleria fowleri - Primary amoebic encephalitis (PAM)
- Cosmopolitan
- Free-living amoeba in soil and water habitats
- Facultative parasite of the CNS causing
Primary Amoebic Meningoencephalitis (PAM) - Exists as trophozoite and cyst
Trophozoite Naegleria fowleri
- Round clear nucleus with large, central
nucleolus - Two reversible, motile forms
Amoeboid form of Naegleria fowleri
- Occurs in soil, tissue or culture
- Moves by broad pseudopods
- Reproduces by binary fission
Flagellate form of Naegleria fowleri
Occurs in soil, tissue or culture
Naegleria fowleri life cycle
- Flagellate forcibly inhaled during swimming in contaminated water
- Flagellate then transforms into amoeboid form, enters brain via olfactory neuroepithelium
- Multiplies profusely by binary fission
Naegleria fowleri transmission
- Both trophozoite (amoeboid and flagellated) forms are infective
- Organism can withstand high chlorination
- Tolerate high temperature (46ºC)
- Infection via inhalation of organism in water
Naegleria fowleri clinical features
- Disease confined to brain
- Nest of amoebae with extensive haemorrhagic reaction mostly in the basilar portion of cerebrum and cerebellum
- Infection often fatal
Food and water borne protozoan pathogens
- Giardiasis
- Amoebiasis
- Cryptosporidiosis
- Toxoplasmosis
Giardiasis
A gastrointestinal disease caused by the
flagellate protozoan Giardia intestinalis
Symptoms of giardiasis
- Diarrhea
- Gas or flatulence
- Greasy stools that tend to float (malabsorbtion of fat)
- Stomach or abdominal cramps
- Upset stomach or nausea
- Weight loss and dehydration possible
2 stages of Giardia intestinalis
Trophozoite and cyst
Trophozoite stage of Giardia intestinalis
- The feeding/motile stage
- Symmetrical (tennis racquet like) with 2 nuclei, 4 pairs of flagella
- Unique adhesive disc on ventral
surface (for attachment to intestinal wall)
Life cycle of Giardia intestinalis
- The parasite is shed with the faeces as
cysts (trophozoites may also be released). - Cysts injested by a new host can survive passage to the duodenum.
- In the duodenum two trophozoites
excyst from the cyst. - They reproduce by longitudinal binary
fission, attach to and feed on intestinal epithelial cells. - During periods of diarrhoea trophozoites transported with the intestinal contents encyst and leave the host with the faeces.
Giardia intestinalis transmission
- Faecal-oral route via ingestion of viable cysts
- Person to person: hand-to-mouth, some sexual practices implicated
- Contaminated food and water: Epidemic if water supply contaminated, unhygienic food handlers
Amoebiasis
- Mild to severe gastrointestinal disease caused by the amoeboid protozoan Entamoeba histolytica
- Other species such as Entamoeba. dispar and Entamoeba coli cause infection but are non pathogenic
Clinical presentations of amoebiasis
- .Chronic or asymptomatic
- Invasive intestinal disease
- Invasive extra-intestinal disease
Entamoeba histolytica
- Cysts and tropohozoites passed in
faeces - Ingestion of mature cysts
- Excystation (small intestine) and
release of trophozoites - Trophozoites migrate to the large
intestine - Trophozoites multiply (binary fission) and encyst. Both stages are excreted
- Trophozoites entering the bloodstream can move to extraintestinal sites
Invasive intestinal amoebiasis
- Severe invasive intestinal amoebiasis (amoebic dysentry)
- Rapid onset, bloody/mucousy diarrhea (dysentery)
- Intestinal haemorrhage or perforation
- Weight loss, fatigue
- Trophozoites and cysts passed in faeces
Invasive extraintestinal amoebiasis
- Spread from the intestines to vital
organs - Usually the liver (liver
abscess) - Sometimes the lungs, brain, spleen
- Can be fatal
Amoebiasis transmission
Faecal-oral route by ingestion of viable cysts in contaminated food or water (Unhygienic food-handling, Exposure to faecal matter during sexual contact)
Amoebiasis diagnosis
- Microscopic (trophozoites and cysts in stools)
- Trophozoites with ingested RBCs associated with ulceration of large intestine
Treatment of protozoan infections
- Metronidizole for non-invasive
- Paramomycin for invasive
Cryptosporidiosis
- Diarrhea resulting from infection of intestinal epithelial tissue by the sporozoan parasite Cryptosporidium
- Waterborne
- C. parvum and C. hominis mainly found in humans
Cryptosporidiosis life cycle
- Thick-walled oocysts excreted (faeces, respiratory droplets)
- Ingestion (or inhalation) of oocysts
- Excystation (intestines, lungs) to
release sporozoites - Sporozoites parasitize intestinal cells
and develop as trophozoites - Asexual reproduction occurs
producing merozoites - Merozoites form male and female
gametes - Sexual fusion occurs, producing a
zygote - Zygote germinates to form thickwalled (excreted, transmission) and thin-walled (autoinfection) oocysts
Cryptosporidiosis clinical features
- Watery diarrhea
- Accompanied by dehydration, weight loss, abdominal pain, fever, nausea and vomiting
- Chronic and more severe symptoms
in immunocompromised patients
Cryptosporidiosis transmission
- Faecal oral
- Contact with contaminated water (e.g., drinking or recreational water)
- Food sources serve as vehicles for transmission
- Outbreaks associated with waterparks, community pools, day cares
- Zoonotic transmission
Cryptosporidiosis diagnosis
Microscopy to detect stained acid fast oocysts in faecal samples
Cryptosporidiosis treatment
- Hard to treat as sits under cell membrane but outside cytoplasmic membrane
- Intracellular, extracytoplasmic
Toxoplasma gondii
- Cosmopolitan, zoonotic, intracellular
sporozoan - Causes toxoplasmosis (important
opportunistic infection) - Reproduces asexually and sexually in cat,
definitive host - Wide range of vertebrates hosts
- Asexual reproduction by endodyogeny (2 daughter cells formed within mother cell)
Acquired toxoplasmosis
- Asymptomatic
- Lymphadenopathy with/without fever
- Eye lesions
- Myocarditis
- Acquired from cysts in soil or pseudocysts in undercooked meat.
Congenital toxoplasmosis
- Abortion
- Still birth
- Hydrocephaly, mental retardation and eye lesions
- Acquired by vertical transmission across placenta
Toxoplasmosis in immunodeficient
- Reactivation of latent infection
- Fatal, acute fulminating disease
