L23 Flashcards
Protozoa
- Single celled organisms
- Found in every soil and water habitat
- Size from 2um (Babesia spp) to 20cm
(Xenophyophores) - Most = free living
- Contain organelles common to all eukaryotes
(nuclei, cell membrane, ER, mitochondria, Golgi
bodies, lysosomes, food vacuoles)
Why do you need to know about protozia?
- Because some are major causes of human and animal disease
- mostly in tropical areas
- dangerous for immunocompromised people
- Are eukaryotic and related to humans therefore diff to treat
Direct Protozoa life cycle
only one host in life cycle
Indirect Protozoa life cycle
Two or more host required
Definitive or primary host –Protozoa life cycle
- where parasite
reaches maturity and undergoes sexual reproduction - Have both asexual and sexual reproduction (which normally occurs in definitive host).
Reservoir host – Protozoa life cycle
can harbour pathogen often with minimal effect
Secondary or intermediate host –Protozoa life cycle
where the parasite usually undergoes asexual reproduction
Opportunistic Pathogens
- Usually non-pathogenic or occur from quiescent stage
- Harmless in immunocompetent
- Harmful in immunocompremised
Zoonosis
any disease which can be transmitted to humans from animals
– E.g. East African sleeping sickness, toxoplasma – Most pathogens are zoonotic
Anthroponosis
a disease that is spread from humans to humans.
– E.g. Schistosoma mansoni, West African sleeping sickness, malaria
– Usually implies a pathogen normally but not limited to infecting humans
– Excludes rare/unusual case
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 or vector transmission
- Very common
– Where sexual stages of the life cycle take place is the definitive host – can be human
– Sometimes mechanical but usually one or more
essential life-cycle stages take place.
– Distinction between intermediate host and vector is arbitrary and depends on size, speed of movement and active involvement - e.g. a pig versus a mosquito!
Very few protozoal pathogens in humans are spread by direct contact, most are by either a vector or by consuming contaminated food or water
Trichomonas vaginalis
- Cosmopolitan flagellate,
pathogen of trichomoniasis - asymptomatic in men
- Inhabits female lower genital tract and male urethra and prostate
- Causes vaginitis, urethritis and prostatitis
Trichomonas vaginalis- Morphology
- 4 Anterior flagella
- Undulating membrane attaches posterior flagellum
- Axostyle
Trichomonas vaginalis- Morphology [all]
- Exists only as an ovoid trophozoite
- Four anterior flagella (AF)
- Undulating membrane attaches posterior flagellum (PF) to body
- Axostyle (AX), a central supporting rod, extends posteriorly
- Short survival outside the body
- Succumbs rapidly to temperature above 400C, drying, direct sunlight
Trichomonas vaginalis Life Cycle
- trophozoite reproduces by binary fission
- No cystic stage known;
- Infect by sexual transmission
- Male carrier will infect 100% females
- Transfers partner to partner
Axostyle important for
attachment, and irritation
[Trichomonas vaginalis] Survival requires close association with vaginal, urethral or prostatic tissues,____ of vaginal tissue often prolific:
colonisation
Prolific Trichomonas vaginalis
- Degeneration and desquamation of vaginal epithelium followed by leucocytic inflam.
- Vaginitis resulting in frothy, white discharge
- Vulva and cervix inflam
- Male may be asymp or latent with recurring urethritis
- Prostatitis can occur
Trichomonas vaginalis Diagnosis
- Detection of trophozoites in vaginal secretion or scrapping, prostatic fluid or urine (direct or by PCR)
- Recovery of parasite may be enhanced by culturing samples before microscopic examination
Trichomonas vaginalis prvention
- Treating infected male
- Patience and strict discipline
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 (feeding form) and cyst (many forms)
Naegleria fowleri- trophozoite form
*Round clear nucleus with large, central nucleolus
*Two reversible, motile forms
Naegleria fowleri – amoeboid form
- Occurs in soil, tissue or culture
- Moves by broad pseudopods
- Reproduces by binary fission
Naegleria fowleri – flagellate form
- Occurs in soil, tissue or culture
Naegleria fowleri Life cycle
- Typically, flagellate inhaled during diving, swimming in contaminated water
- Flagellate transforms into amoeboid form, enters brain via olfactory neuroepithelium
- Multiplies profusely by binary fission
What naegleria fowleri forms are infective
Both trophozoite (amoeboid and flagellated)
Naegleria fowleri – Transmission and resistence
- inhaled
- withstand high chlorination
- tolerate high temp (46)
- Salination as low as 0.7% seems lethal
Naegleria fowleri –
Pathogenesis in brain
- disease confined to brain
*Nest of amoebae with extensive haemorrhagic reaction in the basilar portion of cerebrum and cerebellum
*Infection often fatal despite early or intensive treatment
Naegleria fowleri –
*Nest of amoebae with extensive haemorrhagic reaction in the basilar portion of ___ and ____
cerebrum and cerebellum
Naegleria fowleri –
Diagnosis
- History of swimming in stagnant water 3-6 days before onset of severe meningitis or meningoencephalitis
- Detection of trophozoites in cerebral spinal fluid
Naegleria fowleri –
prevention
- Salination of pool
- Avoid swimming in doubtful water
Naegleria fowleri –
treatment
- Amphotericin B given intravenously or intrathecally the only drug known to have some success
- Almost always fatal- very acute
