GIS W5 Parasitology

Question 1

Name the Protozoan (unicellular eukaryote) parasites

Answer 1

i) Giardia
ii) Cryptosporidium
iii) Entamoeba

Question 2

Name the Helminths (multicellular eukaryote)

Answer 2

i) Ascaris
ii) Trichuris
iii) Enterobius
iv) Ancylostoma/Necator
v) Strongyloides …and Schistosoma, a fluke
vi) Diphyllobothrium
vii) Echinococcus
viii) Taenia

Question 3

Often not treated with antiparasitics but __________ is especially important

Answer 3

Fluid replacement

Question 4

most common intestinal parasite in US

Answer 4

11) Giardia lamblia (intestinalis)

Question 5

e) Mechanism: presence of parasite causes loss of epithelial absorptive surface area. Other factors may play a role, not well understood.

Answer 5

11) Giardia lamblia (intestinalis)

Question 6

g) Symptoms useful for diagnosis:
i) Foul-smelling diarrhea
ii) Flatulance
iii) Stools are greasy, tend to float (fatty)
iv) Malabsorption of fat, lipids, some vitamins

Answer 6

11) Giardia lamblia (intestinalis)

Question 7

b) Often seen when a sanitation system fails
i) Pool/waterpark chlorination/UV treatment
ii) Storms or issues with drinking water
c) Diarrhea symptoms for 1-2 weeks to ~30 days, may seem to resolve and then come back

Answer 7

12) Cryptosporidium parvum

Question 8

d) Mechanism: Absorption impaired and secretion enhanced when intestinal epithelial cells are infected by Cryptosporidium

Answer 8

12) Cryptosporidium parvum

Question 9

a) Causes Amebiasis
i) AKA Amebic Dysentery, Amebic liver abscesses
b) More prevalent in tropical/subtropical climates
c) Only 10-20% of infected individuals will become ill

Answer 9

13) Entamoeba histolytica

Question 10

i) Bloody, mucus-ey loose stool
ii) Relatively mild symptoms but
iii) Can invade the liver and form an abcess
iv) X-ray/ultrasound to detect abscess or tissue damage

Answer 10

13) Entamoeba histolytica

Question 11

iv) Blood vessel invasion:
(1) Amebic hepatitis = single abscess in right lobe; should present with right upper quadrant pain, fever, weight loss
v) Mucosal cell invasion:
(1) Results in replication,
(2) Cysts in feces

Answer 11

13) Entamoeba histolytica

Question 12

i) Class: Nitroimidazoles
ii) Distribution: Tissue antiparasitic- low concentration in intestine, oral dose almost completely absorbed with high bioavailability
(1) Despite this, it is the drug of choice to treat symptomatic Giardia infection, even though organism that does not penetrate the epithelium!!

Answer 12

a) Metronidazole, Tinidazole

Question 13

iv) Mechanism of action:
(1) Drug breakdown  toxic metabolites that generate free radicals  induce DNA strand breakage
v) Toxicity:
(1) Disulfiram reaction, avoid alcohol
(2) Disturb normal GI flora

Answer 13

a) Metronidazole, Tinidazole

Question 14

i) Mechanism: Essential to anaerobic energy metabolism -interferes with pyruvate::ferredoxin oxidoreductase enzyme dependent electron transfer
ii) Selectivity: Species difference in electron transfer

Answer 14

b) Nitazoxanide

Question 15

iii) Distribution: Rapidly metabolized to tizoxanide. Parent compound is not detected in plasma

Answer 15

b) Nitazoxanide

Question 16

i) Mechanism: Unknown
ii) Toxicity:
iii) loss of visual acuity
iv) Use with caution in patients with thyroid disease – its use interferes with certain thyroid tests
v) Distribution: only 10% of the drug is absorbed so it works locally on the protozoa including cysts in the GI tract, luminal antiparasitic (amebicide)

Answer 16

c) Iodoquinol

Question 17

i) Mechanism: Aminoglycoside- targets ribosomal 30S subunit
ii) Toxicity: Diarrhea, other GI effects including issues with intestinal flora because it has activity against some bacteria.
iii) Distribution: Luminal antiparasitic- Minimal absorption after oral administration

Answer 17

d) Paromomycin

Question 18

a) Spectrum: Broad spectrum, many bacteria, but also effective against apicomplexans including Toxoplasma and Cystoisospora (formerly Isospora), and Cyclospora

Answer 18

16) TMP-SMX (Trimethoprim Sulfamethoxazole) “Co-trimoxazole”, “Bactrim”

Question 19

(1) Staple-sized worms
ii) Worldwide distribution, most common helminth infection in US
iii) Symptom: perianal pruritis

Answer 19

a) Enterobius vermicularis

Question 20

22) Soil-transmitted roundworms
i) a few mm
- Skin penetration

Answer 20

b) Strongyloides

Question 21

22) Soil-transmitted roundworms
i) 9-11 mm (small staple size)
- skin penetration

Answer 21

a) Necator

Question 22

22) Soil-transmitted roundworms
i) 3-5 cm
- egg ingestion

Answer 22

c) Trichuris

Question 23

22) Soil-transmitted roundworms
i) 15-35 cm (spaghetti, a ruler)
- egg ingestion

Answer 23

d) Ascaris

Question 24

formed from the breakdown of eosinophils and may be seen in the stool or sputum of patients with parasitic diseases. Cause may or may not be a parasitic infection, may be asthma.

Answer 24

ii) Charcot-Leyden crystals

Question 25

a) Broad-spectrum benzimidazole drugs
b) Roundworms and tapeworms
c) Distribution: Limited oral absorption,
d) Mechanism: Binds to parasite β-tubulin and inhibits the formation of microtubules

Answer 25

31) Albendazole and Mebendazole

Question 26

cholinergic antihelmintics

b) Mechanism:
i) selectively opens a restricted subgroup of nematode acetylcholine receptor (AChR) ion channels in nematode nerve and muscle. Results in depolarization entry of calcium through the opened channels, and an increase in sarcoplasmic calcium, producing spastic muscle contraction the parasite is then unable to maintain its location (often in the intestine) and is then swept away, effecting the cure.

Answer 26

32) Pyrantel pamoate and Levamisole

Question 27

a) A macrocyclic lactone
b) Mechanism: Binds to glutamate-gated chloride channels in invertebrate nerve and muscle cells, causing deactivation of channel: worm paralysis and death by starvation
c) Resistance: efflux transporters

Answer 27

33) Ivermectin

Question 28

Tapeworms:
i) 3 – 10M in length!
Your typical human tapeworm, beef or pork tapeworm

Answer 28

b) Taenia

Question 29

Tapeworms:

c) fish tapeworm
i) The monster: up to 30 ft in length

Answer 29

Diphyllobothrium

Question 30

Tapeworms:
Causes echinococcocis, a disease of liver, lungs, brain, and other organs
i) Tiny, a few mm in length

Answer 30

d) Echinococcus

Question 31

39) Antiparasitics targeting tapeworms
i) Albendazole and Mebendazole
ii) Also target GI roundworms

Answer 31

a) Benzimidazoles

Question 32

39) Antiparasitics targeting tapeworms
i) Mechanism: increased permeability of the parasite to divalent cations leading to contraction of the worm’s musculature

Answer 32

b) Praziquantel

Question 33

a) Mechanism: Symptoms are caused by immune response to egg stage

Answer 33

42) Schistosomiasis

Question 34

Swimmers itch treatment

Answer 34

i) Antiparasitic: praziquantel

d) Steroid medication (corticosteroids