Parasites

Question 1

Helminths

Answer 1

• worms

- reproduce sexually, usually within host

Question 2

Protozoa

Answer 2

• unicellular

- replicate quickly and asexually in host

Question 3

Cestodes

Answer 3

• tapeworms
• hermaphroditic
• segmented
• eg. Taenia solium
• infection by egg/larval ingestion

Question 4

Nematodes

Answer 4

• unsegmented
• roundworms
• sexes separate
• eg. Strongyloides stercoralis, Ascaris lumbricoides

Question 5

Trematodes

Answer 5

• flat worms or flukes
• unsegmented
• hermaphroditic
• go through intermediate hosts: snails, shellfish
• eg. Schistosoma spp.

Question 6

Schistosomiasis Life Cycle

Answer 6

• eggs hatch in environment producing miracidia
• miracidia infect snails
• cercariae leave snails and penetrate skin of human
• becomes schistosomulae and enters circulation, migrates to portal blood of liver
• paired adult worms migrate to venules of rectum and bowel, lay eggs that go through liver and are excreted into environment

Question 7

Schistosomiasis Clinical Presentation

Answer 7

• 4 weeks post exposure presents as traveler’s diarrhea, urticaria, eosinophilia
• chronic pathology due to egg production, lost eggs can irritate mucosa, retained eggs can become obstructive, can affect liver function (portal hypertension)

Question 8

Schistosomiasis Distribution

Answer 8

• mostly in Africa

- some in Asia and South Africa

Question 9

Schistosomiasis Treatment

Answer 9

• population based treatment is best

- treat school aged children with antihelminths

Question 10

Strongyloides stercoralis Life Cycle

Answer 10

• larvae excreted in stool
• larvae develop into adults, reproduce sexually
• larvae mature into filariform larvae that penetrate skin and initiate infection
• filariform larvae hematogenously spread to lungs, get coughed up and swallowed into intestine
• develop into adults, adult female produces eggs that develop into larvae
• larvae either excreted or auto infect and restart cycle without leaving human

Question 11

Strongyloidiasis

Answer 11

-autoinfection can lead to hyper infection, producing GI hemorrhage, pneumonitis

Question 12

Malaria

Answer 12

• most important parasitic disease worldwide

- majority of deaths in sub-Saharan Africa

Question 13

Malaria Vector

Answer 13

Female anopheles mosquito

Question 14

Malaria Parasite

Answer 14

-Plasmodium species (falciparum, vivax, knowlesi, ovale, malariae)

Question 15

Schizogany

Answer 15

-asexual cycle in RBC’s and other tissues

Question 16

Sporogany

Answer 16

-sexual cycle in female anopheles mosquito

Question 17

Plasmodium Life Cycle

Answer 17

• Plasmodium in mosquito gut
• migrate to salivary glands
• mosquito bites human, Plasmodium transferred to human
• Plasmodium infects liver cells, replicates there (becomes hepatic schizont, eventually ruptures)
• Plasmodium released from liver cells into RBC’s, infects RBCS, becomes blood-stage schizont (bunch of Plasmodium in single cell)
• Parasite picked up by a mosquito

Question 18

P. falciparum

Answer 18

• minimal temp for devo in mosquito - 16
• no dormant liver stage, no relapse
• 5% cases are severe, causes majority of deaths
• treated with Arteminsin Combo Therapy
• common asymptomatic carriage
• more common in Africa

Question 19

P. vivax

Answer 19

• minimal temp for devo in mosquito - 15
• dormant liver stage, relapse both can occur
• asymptomatic carriage is very common
• treatment chloroquine and primaquine
• primaquine gets rid of hypnozoite

Question 20

Malaria stable transmission

Answer 20

• more than 10 ix’s per year
• most deaths occur in children
• by adulthood, have asymptomatic parasitemia
• sub-Saharan Africa, Asia
• lost with immigration

Question 21

Unstable transmission

Answer 21

• immunity does not develop
• less than 5 ix’s per year
• major epidemics
• Africa and Asia

Question 22

Malaria Diagnostics

Answer 22

• Microscopy and blood smear (thick and thin), can determine species and parasitemia
• Rapid Antigen Test (quick results, can’t determine parasitemia, can’t pick up non-falciparium malaria, need microscopy follow up)
• PCR

Question 23

Uncomplicated malaria

Answer 23

• fevers, rigors, headache, myalgia
• often mistaken as viral ix
• tx: Atovaquone-Proguanil (attacks hepatic and blood schizonts)
• if known it’s not falciparum - chloroquine-primaquine

Question 24

Severe malaria

Answer 24

• coma, metabolic acidosis, pulmonary edema, hypoglycemia, renal failure
• mortality - 10-20% w/treatment
• tx: Artesunate + Doxycycline/Clindamycin

Question 25

Malaria and Travel

Answer 25

- #1 cause of fever in return traveler's - 50% is falciparum - often due to lack of prophylaxis or improper prophylaxis regimen

Question 26

Malaria Prophylaxis

Answer 26

- varies with travel destination, cost, side effects, activities, duration - mefloquine and chloroquine are weekly - atovaquone-proguanil and doxycycline are daily

Question 27

Taenia solium Life cycle

Answer 27

- pigs acquire parasite from environment - parasite into muscle tissue - humans consume undercooked pig, infected with tapeworm - tape worm in GI tract, releases proglottids with eggs - human ingests eggs, can lodge in brain, eyes, skeletal muscle

Question 28

Taenia solium Epidemiology and Distribution

Answer 28

- most common parasite of CNS - preventable form of epilepsy - found in South America, Africa and Asia