Pathogenic Protozoa Flashcards
definitive host vs intermediate host
definitive host: in which parasite undergoes sexual cycle (meiosis + fertilization)
intermediate host: in which parasite multiples asexually
trophozoite vs cyst
trophozoite: growing/multiplying form of parasitic protozoan
cyst: non-growing form, specialized for resistance to unfavorable environment and/or dispersal
host vs reservoir
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
mutualism vs commensalism vs parasitism
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
which is a more common diagnostic technique for protozoa, culture or microscopy?
microscopy more common (direct smears, tissue histology)
also use serology and nucleic acid amplification
what kind of illness does Giardia lamblia (flagellate protozoa) cause?
Beaver fever/ Backpacker’s diarrhea (widespread in wilderness, fecal/oral) —> non-invasive diarrhea
what kind of illness does Trichomonas vaginalis (flagellate protozoa) cause?
STI: vaginitis (F), urethritis (M)
how are hemoflagellates transmitted?
insect vector, multiply in both vector and host
include: Trypanosoma (blood/tissue infections, multiply outside cells) and Leishmania (tissue infections, multiple inside cells)
what are the 4 stages of mutation of hemoflagellates (Trypanosoma)?
A PET:
Amastigote
Promastigote
Epimastigote
Trypomastigote
kinetoplast (mitochondria + basal body) progressing moves posterior
how do trypanosomes (hemoflagellate) evade the immune system?
antigenic phase variation of variable surface glycoprotein (VSG), of which they have 1000s and express only 1 at a time
what is the vector for Trypanosoma brucei and what illness does it cause? name its 3 subspecies
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
what is the infective and diagnostic stage, respectively, of the life cycle of Trypanosoma brucei, which causes African sleeping sickness?
infective stage: tsetse fly takes blood meal and injects trypomastigotes
diagnostic stage: circulating trypomastigotes in blood during acute phase (undetectable when latent)
what are the 2 stages of African Sleeping Sickness, and what protozoa causes it?
Trypanosoma brucei
Stage 1 (early): parasite in peripheral circulation
Stage 2 (late): parasite crosses BBB —> neurological symptoms, lymphadenopathy
what kind of infections do Trypanosoma (hemoflagelletes) cause, and where do they multiply?
blood and tissue infections, multiply outside cells
what is the vector of American trypanosomiasis, caused by Trypanosoma cruzii? what is the infective and diagnostic stage, respectively, of the life cycle?
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
what kind of illness does American trypanosomiasis (Trypanosoma cruzii) cause?
Chagas’ disease (American trypomanosomiasis): primary lesion at site of infection, spreads to conjunctiva (eyelid swelling) /muscle (febrile) / heart /etc
what is the vector of Leishmania (hemoflagellates)?
sandfly
infective stage: sandfly takes blood meal and injects promastigote
diagnostic stage: amastigote multiply within cells of various tissues
what kind of illness does Leishmaniasis (hemoflagellates) cause?
cutaneous, visceral, mucosal
how is Entamoeba histolytica (amoeba) transmitted, and what kind of illness does it cause?
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]
Naegleria and Acanthamoeba amoebas cause what kind of illness?
amoebic meningoencephalitis (from swimming in natural waters, rapidly spread form sinuses to brain)
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)
invade cells and multiply in vacuole
- Trophozoites grow without division
- Schizonts cleave into multiple progeny
- released by cell lysis
what are the intermediate and definitive hosts, respectively, for each of these apicomplexa species:
a. Plasmodium
b. Toxoplasma
c. Cryptosporidium
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)
what are 3 forms of malaria transmission (caused by Plasmodium spp.)?
- bite of Anopheles mosquito
- blood transfusion
- vertical (MTC)
name 4 species of Plasmodium that infect humans (cause malaria)
- P. falciparum (most virulent!)
- P. malariae (2nd most severe)
- P. vivas
- P. ovale
describe the life cycle of malaria as it moves between humans and mosquitos (3 general steps each)
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)
what is different about the life cycle of Plasmodium species P. vivax and P. ovale, and how is this clinically relevant?
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)
describe causes of periodic fevers and blackwater fever, respectively, as seen in malaria infection (by Plasmodium spp.)
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]
regarding malaria (caused by Plasmodium), what does “exoerythrocytic schizogony” mean?
refers to hepatocyte invasion (upon initial infection) and asexual replication (before breaking out to infect RBCs)
regarding malaria infection (by Plasmodium), what does “erythrocytic schizogony” mean?
refers to Plasmodium division in RBC (after initial replication in hepatocytes)
- merozoite invades rbc, develops into ring form
- ring form enlarges into trophozoite
- nuclear division produces immature schizont
- cytoplasmic cleavage produces schizont
- cell lysis releases new merozoites
what is the main element of malaria prevention? (caused by Plasmodium)
vector control (removal of breeding sites, mosquito nets)
active infection of malaria confers premunition - explain what this is
premunition: immunity which prevents superinfection with the same species (wanes on recovery)
explain why malaria infection does not confer long-lasting immunity
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
what kind of illness does Babesia, an apicomplexa protozoa, cause?
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
Cryptosporidium, Cyclospora, and Cystoisospora are all apicomplexa that cause ____
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)
how is Cryptosporidium, an apicomplexa protozoa which causes diarrhea, diagnosed?
acid-fast cysts in stool or cysts stained with fluorescent antibody
humans are both definitive and intermediate host
what kind of diarrheal illnes does Cryptosporidium cause?
non-invasive diarrhea: parasites adhere to apical surface of intestinal epithelium and divide there
CRYPTosporidium stay in the CRYPTs
where does Toxoplasma infection come from?
most often from cysts (oocysts) in cat litter-boxes, occasionally from contaminated meat
who is at risk for serious infection by Toxoplasma?
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)
how does Toxoplasma disseminate in the body?
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
