L23

Question 1

Protozoa

Answer 1

• 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)

Question 2

Why do you need to know about protozia?

Answer 2

• 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

Question 3

Direct Protozoa life cycle

Answer 3

only one host in life cycle

Question 4

Indirect Protozoa life cycle

Answer 4

Two or more host required

Question 5

Definitive or primary host –Protozoa life cycle

Answer 5

• where parasite
  reaches maturity and undergoes sexual reproduction
• Have both asexual and sexual reproduction (which normally occurs in definitive host).

Question 6

Reservoir host – Protozoa life cycle

Answer 6

can harbour pathogen often with minimal effect

Question 7

Secondary or intermediate host –Protozoa life cycle

Answer 7

where the parasite usually undergoes asexual reproduction

Question 8

Opportunistic Pathogens

Answer 8

• Usually non-pathogenic or occur from quiescent stage
• Harmless in immunocompetent
• Harmful in immunocompremised

Question 9

Zoonosis

Answer 9

any disease which can be transmitted to humans from animals
– E.g. East African sleeping sickness, toxoplasma – Most pathogens are zoonotic

Question 10

Anthroponosis

Answer 10

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

Question 11

Direct Transmission

Answer 11

– Passed directly from one infected host to another by
some physical means or from the environment

Question 12

Food or waterborne transmission

Answer 12

From contaminated food or water Fecal – oral route

Question 13

intermediate host or vector transmission

Answer 13

• 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!

Question 14

Very few protozoal pathogens in humans are spread by direct contact, most are by either a vector or by consuming contaminated food or water

Question 15

Trichomonas vaginalis

Answer 15

• Cosmopolitan flagellate,
  pathogen of trichomoniasis
• asymptomatic in men
• Inhabits female lower genital tract and male urethra and prostate
• Causes vaginitis, urethritis and prostatitis

Question 16

Trichomonas vaginalis- Morphology

Answer 16

• 4 Anterior flagella
• Undulating membrane attaches posterior flagellum
• Axostyle

Question 17

Trichomonas vaginalis- Morphology [all]

Answer 17

• 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

Question 18

Trichomonas vaginalis Life Cycle

Answer 18

• trophozoite reproduces by binary fission
• No cystic stage known;
• Infect by sexual transmission
• Male carrier will infect 100% females
• Transfers partner to partner

Question 19

Axostyle important for

Answer 19

attachment, and irritation

Question 20

[Trichomonas vaginalis] Survival requires close association with vaginal, urethral or prostatic tissues,____ of vaginal tissue often prolific:

Answer 20

colonisation

Question 21

Prolific Trichomonas vaginalis

Answer 21

• 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

Question 22

Trichomonas vaginalis Diagnosis

Answer 22

• 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

Question 23

Trichomonas vaginalis prvention

Answer 23

• Treating infected male
• Patience and strict discipline

Question 24

Trichomonas vaginalis treatment

Answer 24

Metronidazole

Question 25

Naegleria fowleri – Primary amoebic encephalitis (PAM)

Answer 25

*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)

Question 26

Naegleria fowleri- trophozoite form

Answer 26

*Round clear nucleus with large, central nucleolus
*Two reversible, motile forms

Question 27

Naegleria fowleri – amoeboid form

Answer 27

• Occurs in soil, tissue or culture
• Moves by broad pseudopods
• Reproduces by binary fission

Question 28

Naegleria fowleri – flagellate form

Answer 28

• Occurs in soil, tissue or culture

Question 29

Naegleria fowleri Life cycle

Answer 29

• Typically, flagellate inhaled during diving, swimming in contaminated water
• Flagellate transforms into amoeboid form, enters brain via olfactory neuroepithelium
• Multiplies profusely by binary fission

Question 30

What naegleria fowleri forms are infective

Answer 30

Both trophozoite (amoeboid and flagellated)

Question 31

Naegleria fowleri – Transmission and resistence

Answer 31

• inhaled
• withstand high chlorination
• tolerate high temp (46)
• Salination as low as 0.7% seems lethal

Question 32

Naegleria fowleri –
Pathogenesis in brain

Answer 32

• 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

Question 33

Naegleria fowleri –
*Nest of amoebae with extensive haemorrhagic reaction in the basilar portion of ___ and ____

Answer 33

cerebrum and cerebellum

Question 34

Naegleria fowleri –
Diagnosis

Answer 34

• History of swimming in stagnant water 3-6 days before onset of severe meningitis or meningoencephalitis
• Detection of trophozoites in cerebral spinal fluid

Question 35

Naegleria fowleri –
prevention

Answer 35

• Salination of pool
• Avoid swimming in doubtful water

Question 36

Naegleria fowleri –
treatment

Answer 36

• Amphotericin B given intravenously or intrathecally the only drug known to have some success
• Almost always fatal- very acute