Parasitic Pathogens

Question 1

Describe the life cycle of common pathogenic protozoa, especially the sporozoa

Answer 1

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)

Question 2

What is parasitology?

Answer 2

study of parasites and their relationships to their hosts

Question 3

Define phoresis

Answer 3

2 organisms that live together, but have no effect on one another

Question 4

Describe the effects of a parasite

Answer 4

• 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

Question 5

What is the structure of a parasite and how are they classified?

Answer 5

• unicellular or multicellular eukaryotes
• many phyla, cross-kingdom
• classified by life cycles and locomotion

Question 6

Define intermediate host and definitive (final) host

Answer 6

intermediate host: adult or sexual reproduction (protozoa)

definitive host: larvae or asexual reproduction (protozoa)

Question 7

List the common pathogenic protozoa

Answer 7

• sporozoa
• amoeba
• flagellates
• ciliates

Question 8

Compare in general terms the life cycles of nematodes and platyhelminths (trematodes and cestodes)

Answer 8

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

Question 9

Describe the ways by which parasites evade detection by host immunity

Answer 9

• 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

Question 10

Which parasites are protozoa?

Answer 10

• 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

Question 11

What form are flagelletes in blood and tissues?

Answer 11

anthropod vector

Question 12

What form are flagelletes in GI tract?

Answer 12

cysts

Question 13

Which parasites are helminths?

Answer 13

-roundworms: circular cross-section, no segments
-flatworms: symmetric
- flukes: short, nonsegmented
- tapeworms: segmented; each is self contained
(many colonies)

Question 14

In the case of malarie, who is the definitive and intermediate host?

Answer 14

Human is intermediate

Mosquito is definitive

Question 15

What is the vegetitative state of malaria?

Answer 15

merozoites

Question 16

What diseases does sporoza cause and what’s its mode of transmission?

Answer 16

• 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)

Question 17

What diseases do amoebas cause and what’s their mode of transmission?

Answer 17

• 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

Question 18

What diseases do flagellates cause and what’s their mode of transmission?

Answer 18

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

Question 19

What diseases do ciliates cause and what’s their mode of transmission?

Answer 19

-Balantidium coli: causes diarrhea, only know human ciliate pathogen

Question 20

Occurence of protozoa infections diagram

Answer 20

see slide 19

Question 21

What are the 2 classes of platyhelminthes?

Answer 21

Class trematodes: flukes

Class Cestodes: tapeworms

Question 22

General characteristics of parasitic worms

Answer 22

• 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

Question 23

How are helminths transmitted?

Answer 23

• active skin penetration
• injection by blood sucking insect
• fecal-oral route
• intermediate host

Question 24

Why are helminth infections more common in children?

Answer 24

poor hygeine

Question 25

Examples of tissue infections by adult nematodes

Answer 25

• 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

Question 26

Define cysticerci

Answer 26

tapeworm cyst

Question 27

Define cercariae

Answer 27

free swimming larval stage of liver fluke

Question 28

Define metacercariae

Answer 28

encysted larva of liver fluke

Question 29

Explain Liver Fluke cycle

Answer 29

• 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

Question 30

When are humans the intermediate host for helminths?

Answer 30

Taenia solium

Question 31

What is an ectoparasite?

Answer 31

live on outside of body

Question 32

Difference between biological and mechanical vectors

Answer 32

Biological: a host in life cycle of parasite (mosquito carrying malaria)
Mechanical: ex. house flies carrying salmonella