Parasitology - Lecture 3

Question 1

What do parasites broadly require?

Answer 1

Require a host organism to survive/propagate

-includes viruses, bacteria, symbiotic organisms

Question 2

What is a prarasite biologically?

Answer 2

Eukaryotic organisms which live on or in a host organism, and which utilize its resources for their own survival and propagation

Question 3

What are the two classifications of parasites?

Answer 3

Protazoa - unicellular

Metazoa - multicellular (include helminths (internal) and ectoparasites (external))

Question 4

How do parasites replicate?

Answer 4

Replicate extracellularly

Question 5

Where do parasites largely infect?

Answer 5

The GI tract and blood

Question 6

How are parasitic infections (GI and blood) transmitted?

Are they communicable?

Answer 6

• GI tract infections typically transmitted via fecal:oral route
• Blood infections typically transmitted via animal vector
• Many parasitic infections are not communicalbe

Question 7

Where do parasites typically complete their life cycle?

Answer 7

Many complete their life cycle in TWO species:

• Definitive host - sexual stage of reproduction is complete (Primary Host)
• Intermediate host - non-sexual stages of reproduction are completed - parasite may not reproduce at this stage, or may undergo differentiation

Question 8

What are the four classifications of Protozoa?

Answer 8

Amoeba (sacrodina)

Flagellates (mastigophora)

Ciliates (ciliophora)

Spore-forming (apicomplexa)

Question 9

Describe amoebas:
nutrient
movement
human pathogen

Answer 9

Obtain nutrients via phagocytosis

Move via pseudopodia

• push out cytoplasm to produce ‘false feet’
• conversion of ectoplasm to endoplasm and vice versa allow amoeboid movement

Entamoeba histolytica (intesinal amoebiasis)

Question 10

How are amoebas infections acquired?

Answer 10

Through ingestion of contaminated food and water

Question 11

Describe nonivasive vs invasive ameoba infection

Answer 11

A noninvasive infection is the formation of a cyst that exits the host in stool

An invasive infection happens with trophozoites invade the intestinal mucousa, travel the blood stream infecting sites such as the liver, brain and lungs

Question 12

Describe flagellates:
movement
human pathogen

Answer 12

Longe flagella that whip to facilitate movement
Organism may bear one or multiple flagella
Variety of cellular structures between flagellated protazoan parasites

Giardia lambia (giardiasis)
Trichomonas vaginalis
Trypanosoma cruzi

Question 13

How are flagellate infections acquired?

Answer 13

Through ingestion of a mature cyst (cysts can survive weeks to months in cold water, but only cysts can survive outside host)

Question 14

Describe ciliates

Answer 14

Cilia provide motility and aid in feeding (phagocytosis)
variety of feeding strategies and cellular sturctures

Balantidum coli - only human pathogen

Question 15

Overview the general protozoan life cycle

Answer 15

Cyst stage - infective

• cysts are hearty, resist extreme environmental conditions
• may survive long periods of time outside a host organism
• may be the product of sexual reproduction in protazoa

Excystation
–occurs in the host organism and typically yeilds a trophozoite

Trophozoite
-feeding/proliferation stage (asexual reproductive stage)

Question 16

Describe sporozoa (apicomplexa)

Answer 16

Have a complex subcellular strucure

• apical complex structure (may aid in entry)
• apicoplast organelle (potential functions include fatty acid synthesis, heme synthesis)

Question 17

Describe the general life cycle stages of sporozoa

Answer 17

Sporogony yields oocysts and sporozoites
Merogony yields shizonts and merozoites
Gametogony yields gametes and zygots

Question 18

Give four example of sporozoa human pathogens

Answer 18

Cryptosporidium
Toxoplasma gondii
Falciparum (malaria)
Babesia

Question 19

List the different malaria names…

Answer 19

Plasmodium falciparum - most severe
Plasmodium malariae
Plasmodium vivax
Plasmodium ovale
Plasmodium knowlesi

Question 20

Describe vector-borne infections

Answer 20

May be animate or inanimate

Inanimate vectors are mechanical - facilitate spread of pathogen

Question 21

What are the animal vectors commonly?

Answer 21

Arthopods - mosquitoes, fleas, flies

Rodents - mice, rats

Question 22

Are vector-borne infections contagious?

Answer 22

Not contagious IF an essential stage of the pathogen’s life cycle takes place in the vectore species

• Malaria - sexual reproduction stages occur in the mosquito
• Giardiasis - all stages of reproduction occur in humans even though the parasite infects dogs, cats, cattle, beavers

Question 23

How is the pathogen controlled?

Answer 23

Controlled through vector control

-Epidemiology of vector-borne infections is closely related to ecology and climate, prevalence of vector

Question 24

Describe helminths

Answer 24

Multicellular parasites

Typically infect the GI tract

Question 25

How are helminths classified?

Answer 25

Classified by shape

• Platyhelmiths (‘flat’) - cestodes and trematodes
• Nematodes (‘threads’)

Question 26

What are trematodes?

Answer 26

Flukes and flatworms

Question 27

Describe trematodes
sexual
host
structure

Answer 27

Dioecious or hermaphoraditic
Require at least 1 intermediate host (mollusk)
-sexual reproduction occurs in the definitive host
-asexual stages of reproduction occur in intermediate host
Complex organismal structure
-reproductive system
-nervous system
-GI-like system

Question 28

Give three examples of trematode human pathogens and where they infect

Answer 28

Schistosoma (blood - schistomiasis)
Paragonimus westermani (lung)
Fasciola hepatica (liver)

Question 29

How do trematodes infect humans?

Answer 29

Infect human by penetrating skin

Question 30

What are cestodes?

Answer 30

Tapeworms

Question 31

Describe cestodes
structure
adult vs larval infection

Answer 31

Segmented, hermaphroditic (each segment), macroscopic

Adult tapeworms lead to intestinal infections

Larval infection leads to extra-intestinal cyst deposition

Question 32

Give four examples of cestode human pathogens and where they come from

Answer 32

Taenia solium (pork)
Taenia saginata (beef)
Diphyllobothrium latum (fish)
Echinococcus (dogs)

Question 33

how do cestodes infect humans?

Answer 33

Infect humans by ingesting undercooked

Question 34

What are nematodes?

Answer 34

Roundworms
Dioecious
Intestinal and extra-intestinal pathogens

Question 35

Give four examples of nematode human pathogens

Answer 35

Enterobias vermicularis (pinworm)
Necator americanus (hookworm)
Trichura trichiuris (whipworm)
Ascaris lumbricoides (giant roundworm)

Question 36

How do nematodes infect humans?

Answer 36

Infect human by ingestion of embryonated eggs