Parasitiology Exam 1

Protozoa

single cell

Helminths

multi-celled

Ectoparasites体外寄生虫

insects, arachnids, etc.

arthropods that attach or burrow into the skin and remain there for relatively long periods of time

Pseudopodia (Protozoan Locomotion)

1. Protruding of pseudopodia

2. formation of new adhesions

3. development of traction

4. release of old adhesions

Definitive host

organism where reproductive cycle occurs (may serve as a reservoir)

Intermediate host

harbors parasite for transition period, often when asexual cycle occurs

Accidental host & Dead end host

atypical host in which the organism may not develop, or just may not be able to complete lifecycle

who is at risk of getting parasite infection

minorities, immigrants and poor/disadvantaged people

Apicomplexan structure

1. polar ring: critical for parasite morphology and host cell invasion

3. microenemes: crucial for host cell recognition, gliding motility, and active invasion

4. Rhoptries: specialized secretory organelle that release their contents during host cell invasion.

Recrudescence

recurrence of asexual parasite which (for any reason) originates from the same parasites responsible for the initial illness.

Relapse

recurrence of asexual parasite from hypnozoite(s) after earlier elimination of iRBC stages.

Recurrence

renewed asexual parasite, which is easily recognized if blood stages appear following drug treatment (can be due to new infection, relapse or recrudescence).

P. falciparum

Only rings observed
Banana-shaped gametocyte
16-32 merozoites

P. vivax

>12 merozoites
Schuffner’s dots /stippling
Ameboid troph
Require Duffy receptor (=“entry point” on RBCs)

P. ovale

Up to 12 merozoites per schizont

Ovale-shaped RBCs

Schuffner’s dots/stippling
Don’t require Duffy receptor (=“entry point” on RBCs)

P. malariae

Band-form trophozoites

Only ~8 merozoites per schizont (often in rosette)

Recrudescing (in blood)

Looks same as P. knowlesi

Why do ‘buffy coats’ work for diagnosing blood parasites?

Density of most blood parasites leads them to accumulate just below the WBCs.

Sporozoite

The infective stage transmitted to a new host.

Trophozoite

The feeding/growing stage of the parasite before reproduction.
inside RBCs.

Merozoite

The daughter cell produced by replication.
Spreads infection from cell to cell.

Cryptosporidium parvum/hominis

Intracellular, extracytoplasmic blue ‘beads’ in the brush border

Cyclospora cayetanesis on modified acid-fast

Cystoisospora belli’s oocyst under Iodine Stain

Cystoisospora belli’s sporoblast/sporocyst under Iodine Stain

Cystoisospora modified acid fast staining

Pink/red/purple oocysts
blue-green background
Typical ellipsoidal shape

Cystoisospora on Hematoxylin and Eosin (H&E) stain

Toxoplasma gondii: tachyzoites

Toxoplasma gondii: tissue cysts containing bradyzoites

Toxoplasmosis: if a patient is IgM is positive, but IgG is negative, what to do next?

suspect Acute infection or false-positive

perform another serological test in 1–2 weeks
- if the result remain the same → false-positive IgM

• because if there is an infection, the body is going to start producing IgG in 1-2 wks of infection

- if the result of IgG change to positive → then it is acute infection

• becuase Negative IgG = no infection seen at all

Toxoplasmosis: if a patient is both IgM and IgG positive, what to do next?

suspect recent infection within 12 months or False-positive
send the specimen to a reference lab for further testing like IgG/IgM avidity test.

Toxoplasmosis: if a patient is IgG is positive, but IgM is negative, what does that mean?

Infected with Toxoplasma more than 1 year.

Microsporidium

characteristic coiled polar filament

Acid Fast Trichrome Stain of Microsporidium

Chitin stain of Microsporidium

Microsporidia – Jejunal Biopsy