Parasitic Pathogens Flashcards
Describe the life cycle of common pathogenic protozoa, especially the sporozoa
Trophozoite: feeding and dividing stage
Cyst: dormant but infectious stage
sexual reproduction: via conjugation or gametogenesis
asexual repro.: fission or schizogony
SPOROZOA: schizogony: multiple mitosis of nuclei followed by cytoplasmic segmentation (burst)
What is parasitology?
study of parasites and their relationships to their hosts
Define phoresis
2 organisms that live together, but have no effect on one another
Describe the effects of a parasite
- depends on host for life cycle
- harming the host is not desirable
- disease is associated with prolonged, excessive, or repeated exposure
- multiple infections are possible
- subacute or chronic
- many are zooneses – need both human and animal hosts
- unicellular dessicated easily – need vector or encystment
What is the structure of a parasite and how are they classified?
- unicellular or multicellular eukaryotes
- many phyla, cross-kingdom
- classified by life cycles and locomotion
Define intermediate host and definitive (final) host
intermediate host: adult or sexual reproduction (protozoa)
definitive host: larvae or asexual reproduction (protozoa)
List the common pathogenic protozoa
- sporozoa
- amoeba
- flagellates
- ciliates
Compare in general terms the life cycles of nematodes and platyhelminths (trematodes and cestodes)
Nematodes (roundworms):
-tissue infections
-separate sexes - female larger than male
-eggs develop in environment; no need for intermediate host, hatch in GI tract
Platyhelminths (flatworms, flukes, tapeworms):
-intestinal infections most common
-larva act in tissue infections
-cestodes: hermaphrodites, both sexes per segment
-trematodes: hemaphrodites or seprate sexes constantly in conjugation
Describe the ways by which parasites evade detection by host immunity
- immune cells and antibodies target cell membrane
- some change their surface proteins as the immune system begins to recognize them (trypanosoma)
- polymorphism of surface antigens (plasmodium)
- consumtion of compliment – component mimicry (amoeba)
- some worms acquire host molecules as camoflouge
- other worms release copious soluble solutions to divert immune system
Which parasites are protozoa?
- amoebas (trophozoite and cyst forms): pseudopod extension and cytoplasmic streaming
- flagelletes: at least 1 flagella for locomotion
- ciliates: covered in cilia (very unusual)
- apicomplexans (sporozoa): replicate intracellularly; gliding motility allows forced entry into cells
What form are flagelletes in blood and tissues?
anthropod vector
What form are flagelletes in GI tract?
cysts
Which parasites are helminths?
-roundworms: circular cross-section, no segments
-flatworms: symmetric
- flukes: short, nonsegmented
- tapeworms: segmented; each is self contained
(many colonies)
In the case of malarie, who is the definitive and intermediate host?
Human is intermediate
Mosquito is definitive
What is the vegetitative state of malaria?
merozoites
What diseases does sporoza cause and what’s its mode of transmission?
- plasmodium causes malaria (mosquito vector/blood)
- Babesia causes babesiosis (tick vector)
- Toxoplasma causes toxoplasmosis (in fetus and AIDS); fecal-oral transmission
- Cryptosporidium causes diarrhea (in AIDS)
What diseases do amoebas cause and what’s their mode of transmission?
- Entamoeba histolytica (trophozite and cyst stages): amoebaisis (amebic dysentery) – fecal-oral transmission
- Naegleria fowleri: brain-eating ameobic meningocephalitis
- Acanthamoeba: causes amoebic meningocephalitis and contact-lens keratitis
- transmitted through still water
What diseases do flagellates cause and what’s their mode of transmission?
1) Luminal
- Trichomonas vaginalis: trichomoniasis; no cyst stage; only sexually transmitted parasite
- Giardia duodenalis (beaver fever): causes diarrhea, cysts survive for months in water; fecal-oral transmission
2) hemoflagellates (in blood)
- Trypanosoma brucei: causes African trypanosomiasis (sleeping sickness); (Reduviid bug and tsetse bug vector)
- Trypanosoma cruzi: causes American trypanosomiasis (Chagas disease); (Reduviid bug and tsetse bug vector)
- Leishmania: causes kala-azar; (sand-fly vector)
-transmitted via
What diseases do ciliates cause and what’s their mode of transmission?
-Balantidium coli: causes diarrhea, only know human ciliate pathogen
Occurence of protozoa infections diagram
see slide 19
What are the 2 classes of platyhelminthes?
Class trematodes: flukes
Class Cestodes: tapeworms
General characteristics of parasitic worms
- well developed reproductive system
- usually can’t multiply in the same host
- macroparasites – visible to the naked eye
- can produce up to 200,000 eggs/day but none hatch in host
How are helminths transmitted?
- active skin penetration
- injection by blood sucking insect
- fecal-oral route
- intermediate host
Why are helminth infections more common in children?
poor hygeine
Examples of tissue infections by adult nematodes
- Toxicara canis: causes eye infection; natural host is dog
- Trichinella spiralis: causes muscle infection; natural hosts are pigs, bears, etc
- Filaria: causes lymph infection; mosquito-born
Define cysticerci
tapeworm cyst
Define cercariae
free swimming larval stage of liver fluke
Define metacercariae
encysted larva of liver fluke
Explain Liver Fluke cycle
- 2 intermediate hosts
1) eggs passed in human feces
2) eggs ingested by snail - asexual reproduction
3) cercariae attach to fresh water fish
4) we eat fresh water fish
When are humans the intermediate host for helminths?
Taenia solium
What is an ectoparasite?
live on outside of body
Difference between biological and mechanical vectors
Biological: a host in life cycle of parasite (mosquito carrying malaria)
Mechanical: ex. house flies carrying salmonella
