Pathogenic Protozoa

Question 1

definitive host vs intermediate host

Answer 1

definitive host: in which parasite undergoes sexual cycle (meiosis + fertilization)

intermediate host: in which parasite multiples asexually

Question 2

trophozoite vs cyst

Answer 2

trophozoite: growing/multiplying form of parasitic protozoan

cyst: non-growing form, specialized for resistance to unfavorable environment and/or dispersal

Question 3

host vs reservoir

Answer 3

host: organism used by another as source of nutrition and protection

reservoir: organism in which a parasite replicates, from which it is transmitted to host animals

Question 4

mutualism vs commensalism vs parasitism

Answer 4

mutualism: both members benefit

commensalism: symbiont benefits from host but host neither benefits nor is harmed

parasitism: symbiont harms its host or lives at expense of the host

Question 5

which is a more common diagnostic technique for protozoa, culture or microscopy?

Answer 5

microscopy more common (direct smears, tissue histology)

also use serology and nucleic acid amplification

Question 6

what kind of illness does Giardia lamblia (flagellate protozoa) cause?

Answer 6

Beaver fever/ Backpacker’s diarrhea (widespread in wilderness, fecal/oral) —> non-invasive diarrhea

Question 7

what kind of illness does Trichomonas vaginalis (flagellate protozoa) cause?

Answer 7

STI: vaginitis (F), urethritis (M)

Question 8

how are hemoflagellates transmitted?

Answer 8

insect vector, multiply in both vector and host

include: Trypanosoma (blood/tissue infections, multiply outside cells) and Leishmania (tissue infections, multiple inside cells)

Question 9

what are the 4 stages of mutation of hemoflagellates (Trypanosoma)?

Answer 9

A PET:
Amastigote
Promastigote
Epimastigote
Trypomastigote

kinetoplast (mitochondria + basal body) progressing moves posterior

Question 10

how do trypanosomes (hemoflagellate) evade the immune system?

Answer 10

antigenic phase variation of variable surface glycoprotein (VSG), of which they have 1000s and express only 1 at a time

Question 11

what is the vector for Trypanosoma brucei and what illness does it cause? name its 3 subspecies

Answer 11

vector: Tsetse fly

cause African Sleeping Sickness, 3 subspecies:
1. T. b. brucei: ancestral form, livestock
2. T. b. rhodesiense: East Africa, rapidly progressive disease
3. T. b. gambesiense: West Africa, slowly progressive disease

Question 12

what is the infective and diagnostic stage, respectively, of the life cycle of Trypanosoma brucei, which causes African sleeping sickness?

Answer 12

infective stage: tsetse fly takes blood meal and injects trypomastigotes

diagnostic stage: circulating trypomastigotes in blood during acute phase (undetectable when latent)

Question 13

what are the 2 stages of African Sleeping Sickness, and what protozoa causes it?

Answer 13

Trypanosoma brucei

Stage 1 (early): parasite in peripheral circulation

Stage 2 (late): parasite crosses BBB —> neurological symptoms, lymphadenopathy

Question 14

what kind of infections do Trypanosoma (hemoflagelletes) cause, and where do they multiply?

Answer 14

blood and tissue infections, multiply outside cells

Question 15

what is the vector of American trypanosomiasis, caused by Trypanosoma cruzii? what is the infective and diagnostic stage, respectively, of the life cycle?

Answer 15

triatomine bug

infective stage: triatomine but takes blood meal and passes trypomastigote in feces, which enter through bite wound

diagnostic stage: intracellular amastigotes transform into trypomastigotes and burst out of tissue cells to enter bloodstream

Question 16

what kind of illness does American trypanosomiasis (Trypanosoma cruzii) cause?

Answer 16

Chagas’ disease (American trypomanosomiasis): primary lesion at site of infection, spreads to conjunctiva (eyelid swelling) /muscle (febrile) / heart /etc

Question 17

what is the vector of Leishmania (hemoflagellates)?

Answer 17

sandfly

infective stage: sandfly takes blood meal and injects promastigote
diagnostic stage: amastigote multiply within cells of various tissues

Question 18

what kind of illness does Leishmaniasis (hemoflagellates) cause?

Answer 18

cutaneous, visceral, mucosal

Question 19

how is Entamoeba histolytica (amoeba) transmitted, and what kind of illness does it cause?

Answer 19

fecal/oral (ingest cyst, get trophozoites in intestine)

invade/ulcerate intestinal wall, cause liver abscess

[in HISTOLOGY (histolytica), you study tissues, which sometimes develop abscesses]

Question 20

Naegleria and Acanthamoeba amoebas cause what kind of illness?

Answer 20

amoebic meningoencephalitis (from swimming in natural waters, rapidly spread form sinuses to brain)

Question 21

Apicomplexa is a large type of protozoa that includes Cryptosporidium, Toxoplasma, and Plasmodium (among many others). Briefly describe the life cycle of apicomplexa (3 steps)

Answer 21

invade cells and multiply in vacuole

1. Trophozoites grow without division
2. Schizonts cleave into multiple progeny
3. released by cell lysis

Question 22

what are the intermediate and definitive hosts, respectively, for each of these apicomplexa species:
a. Plasmodium
b. Toxoplasma
c. Cryptosporidium

Answer 22

a. Plasmodium
- intermediate: mammal or bird
- definitive: arthropod vector

b. Toxoplasma
- intermediate: rodent, accidental human
- definitive: carnivore

c. Cryptosporidium
- humans are both intermediate and definitive host (fecal/oral)

Question 23

what are 3 forms of malaria transmission (caused by Plasmodium spp.)?

Answer 23

1. bite of Anopheles mosquito
2. blood transfusion
3. vertical (MTC)

Question 24

name 4 species of Plasmodium that infect humans (cause malaria)

Answer 24

1. P. falciparum (most virulent!)
2. P. malariae (2nd most severe)
3. P. vivas
4. P. ovale

Question 25

describe the life cycle of malaria as it moves between humans and mosquitos (3 general steps each)

Answer 25

life cycle in humans:
1. sporozoites from mosquito replicate first in liver
2. merozoites produced, only infectious for RBC
3. gametocytes produced in RBC, infectious for mosquitos

sexual cycle in mosquito:
1. microgametocytes and macrogametocytes (2 types of gametocytes) undergo meiosis
2. fertilization produces oocyst
3. oocyst divides to produce multiple sporozoites (infectious for human hepatocytes)

Question 26

what is different about the life cycle of Plasmodium species P. vivax and P. ovale, and how is this clinically relevant?

Answer 26

other Plasmodium only replicate in liver once, but P. vivax and P. ovale can remain in liver as hypnozoites, causing relapse later

treatment needs to eradicate liver forms (radical cure) and also bloodstream forms (suppressive cure)

Question 27

describe causes of periodic fevers and blackwater fever, respectively, as seen in malaria infection (by Plasmodium spp.)

Answer 27

synchronous RBC lysis and release of merozoites —> periodic fevers

hemolysis from severe infection leads to hemoglobin in urine —> blackwater fever

[also note that P. falciparum, the most virulent, causes capillary occlusion and hemorrhage]

Question 28

regarding malaria (caused by Plasmodium), what does “exoerythrocytic schizogony” mean?

Answer 28

refers to hepatocyte invasion (upon initial infection) and asexual replication (before breaking out to infect RBCs)

Question 29

regarding malaria infection (by Plasmodium), what does “erythrocytic schizogony” mean?

Answer 29

refers to Plasmodium division in RBC (after initial replication in hepatocytes)

1. merozoite invades rbc, develops into ring form
2. ring form enlarges into trophozoite
3. nuclear division produces immature schizont
4. cytoplasmic cleavage produces schizont
5. cell lysis releases new merozoites

Question 30

what is the main element of malaria prevention? (caused by Plasmodium)

Answer 30

vector control (removal of breeding sites, mosquito nets)

Question 31

active infection of malaria confers premunition - explain what this is

Answer 31

premunition: immunity which prevents superinfection with the same species (wanes on recovery)

Question 32

explain why malaria infection does not confer long-lasting immunity

Answer 32

extensive antigenic variation of surface proteins helps Plasmodium continually evade humoral immunity

this also explains why the immune response is weak - antigens seen by the immune system are continually different (esp. considering complex life cycle and intracellular phases which shield from attack)

also why developing a vaccine is difficult

Question 33

what kind of illness does Babesia, an apicomplexa protozoa, cause?

Answer 33

NE US, tick-borne malaria-like illness

high fever chills into fatigue, headache, drenching sweats, muscle aches, etc

only severe in asplenic patients, elderly, otherwise immunocompromised

humans are dead-end hosts, found only in RBC

Question 34

Cryptosporidium, Cyclospora, and Cystoisospora are all apicomplexa that cause ____

Answer 34

cause diarrhea, diagnosis made by identifying eggs in stool

Cryptosporidium: chronic diarrhea in AIDs patients

for all, humans are both definitive and intermediate host (asexual or sexual reproduction)

Question 35

how is Cryptosporidium, an apicomplexa protozoa which causes diarrhea, diagnosed?

Answer 35

acid-fast cysts in stool or cysts stained with fluorescent antibody

humans are both definitive and intermediate host

Question 36

what kind of diarrheal illnes does Cryptosporidium cause?

Answer 36

non-invasive diarrhea: parasites adhere to apical surface of intestinal epithelium and divide there

CRYPTosporidium stay in the CRYPTs

Question 37

where does Toxoplasma infection come from?

Answer 37

most often from cysts (oocysts) in cat litter-boxes, occasionally from contaminated meat

Question 38

who is at risk for serious infection by Toxoplasma?

Answer 38

most healthy people asymptotic or mild illness

immunocompromised: necrosis of muscle, eyes, brain

pregnant: brain damage, blindness, loss of fetus (can cross placenta)

(common - 10-70% adults are seropositive)

Question 39

how does Toxoplasma disseminate in the body?

Answer 39

oocysts (in cat litter boxes) mature into tachyzoites, which are consumed by humans and multiply in gut

from there they spread by macrophages to other tissues