Pathogenesis of Parasites

Question 1

What type of parasite lives on the host and causes infestations?

Answer 1

Ectoparasite

Question 2

What kind of parasite lives in the host and causes infections?

Answer 2

Endoparasite

Question 3

Types of hosts

Answer 3

Definitive
Intermediate
Incidental

Question 4

What type of host harbors adult helminths or sexual stage protozoa?

Answer 4

Definitive host (human with pork tapeworm in intestine)

Question 5

What type of host harbors larval helminths or asexual stage protozoa?

Answer 5

Intermediate host (mosquitoes, pig with tapeworm larva, human with pork tapeworm larva in brain)

Question 6

What’s the deal with incidental hosts?

Answer 6

Unusual. Unnecessary for the maintenance of the parasite in nature.

Question 7

Parasite-host specificity: how picky are they?

Answer 7

Specificity for particular definitive and intermediate hosts.

Often parasite life cycles can only be completed in a particular host.

Question 8

Can we use animal models to study human parasites?

Answer 8

Nah. Parasite won’t thrive.

Question 9

Common routes of parasite entry (6)

Answer 9

Ingestion
Skin/mucosal penetration
Transplacental (prenatal)
Transmammary (milk)
Arthropod bite (vector)
Sexual contact

Question 10

Virulence and pathogenesis depend on what factors?

Answer 10

Infective dose and exposure
Penetration of anatomic barriers
Attachment
Cell/tissue damage
Loss of nutrients
Disruption, evasion, inactivation of host defenses

Question 11

Infective dose and exposure factors of protozoa

Answer 11

Multiply in hosts. Severity of disease may increase as parasites reproduce.

Question 12

Infective dose and exposure factors of helminths

Answer 12

Do not multiply in the definitive host! Worms will die over time unless host is re-exposed.

Severity of the disease is proportional to the initial amount of worms introduced into the host.

Question 13

Penetration of anatomical barriers

Answer 13

Penetrating unbroken skin (Cercaria - causes schistosomiasis)

Question 14

Methods of parasite attachment

Answer 14

Mechanical or biting mouthparts

Molecular interaction

Question 15

Types of mechanical attachment (5)

Answer 15

Oral cavity (capsule)
Attachment organs
Suction disk
Biting mouthparts
Direct penetration (giggity)

Question 16

Hookworm attachment

Answer 16

Ancylostoma tubaeform and caninum have 3 pairs of teeth in the buccal cavity. Attach to intestinal villi.

*0.2ml blood loss per worm per day

Question 17

Tapeworm (Taenia) attachment

Answer 17

Scolex

Question 18

Giardia intestinalis attachment

Answer 18

Attach to villi of small intestine

Question 19

Molecular attachment targets and receptors (4 targets)

Answer 19

Fibroblast: fibronectin and its receptor (Trypanosoma cruzi)

Macrophage: MSP or GP63, and CR2. (Leishmania mexicana)

Erythrocytes: C3b receptor (Babesia)

Duodenal and jejunal epithelium: Lectin and mannose-6-phosphate adherence molecule1 on disk. (Giardia duodenalis)

Question 20

3 methods of cell and tissue damage

Answer 20

Mechanical
Toxic products
Immunopathologic reactions

Question 21

Blockage of internal organs, pressure atrophy, and migration through tissues are what type of tissue damage?

Answer 21

Mechanical

Question 22

What parasite causes cysts in the liver (pressure atrophy)?

Answer 22

Echinococcus granulosus

Question 23

What type of mechanical damage is caused by ascarids, tapeworms, schistosomes, and filrial worms?

Answer 23

Blockage of internal organs

Question 24

What parasite migrates through tissues, causing pathology like Toxocariasis (zoonotic)?

Answer 24

Helminth larva

Question 25

3 types of toxic products produced by parasites

Answer 25

Destructive enzymes - hookworms, schistosomes
Endotoxins - African trypanosomes, malaria
Toxic secretions - tick paralysis

Question 26

Ways a parasite can cause loss of nutrients (3)

Answer 26

Competition with host - fish tapeworm
Interference with host absorption - giardia
Nutrient loss - hookworm (iron)