Protozoal Infections

Question 1

Giemsa Stain

Answer 1

Trypanosomes

Plasmodium

Question 2

Entamoeba histolytica - Pathogenesis

Answer 2

Ingestion of cysts from containated food / water

Cysts become trophozoites in the GI tract and attach to the colonic mucosa, causing “flask-shaped” ulceration

Question 3

Entamoeba histolytica - Presentation

Answer 3

Amebiasis: bloody diarrhea (dysentery) + RUQ pain due to liver abscess

Question 4

Entamoeba histolytica - Diagnosis and treatment

Answer 4

Cysts / trophozoites in stool or tissue (liver abscess)

Stool assay - GalNAc antigen

Serology - Ab assay

Treatment: Luminal disease treated with Paromomycin; liver abscess treated with Metronidazole

Question 5

Giardia lamblia - Pathogenesis

Answer 5

Ingestion of cysts from contaminated food / water

Cysts become trophozoites in the small intestine causing variable crypt hypertrophy / villous flattening

Question 6

Giardiasis - Presentation

Answer 6

Bloating, flatulence, foul-smelling fatty diarrhea

Question 7

Giardia - Diagnosis and Treatment

Answer 7

Cysts / trophozoites in stool

Treated with Metronidazole

Question 8

Cryptosporidium - Pathogenesis

Answer 8

Ingestion of oocytes from contaminated water; may occur in outbreaks from pools, water parks; also sexually transmitted

Question 9

Cryptosporidium - Presentation and Treatment

Answer 9

Mild watery diarrhea in non-immunocompromised; important cause of intractable, severe diarrhea in AIDS patients

Treated with Nitazoxanide (immunocompetent) or Pentamadine (immunocompromised)

Question 10

Trichomonas vaginalis - Pathogenesis and Presentation

Answer 10

Sexual transmission of trophozoite by vaginal / prostatic fluid; causes damage to genital mucosa (microulceration)

Often asymptomatic in men; causes yellow/green discharge and burning/itching vaginitis in women + “strawberry cervix”

Question 11

Trichomonas vaginalis - Diagnosis and Treatment

Answer 11

Diagnosed by demonstration of pear-shaped trophozoite on wet mount

Treated with Metronidazole for patient and partner (prophylaxis)

Question 12

Plasmodium - Pathogenesis

Answer 12

Mosquitos inject sporozites into the blood; sporozoites infect the liver and undergo primary replication to produce merozoites

Merozoites released into blood infect RBCs and undergo asexual reproduction to produce gametes

Gametes in blood are picked up by mosquitos and fuse to form zygotes; zygotes mature to infectious sporozoites in the salivary gland

Question 13

RBC age preferences of Plasmodium sp.

Answer 13

P. vivax and P. ovale - young RBCs
P. malariae - old RBCs
P. falciparum - RBCs of any age

Question 14

Which Plasmodium sp. establish latent infection?

Answer 14

P. vivax and P. ovale can establish latent infection of the liver via the hypnozoite stage

Question 15

Temporal patterns of different Plasmodium sp.

Answer 15

Tertian (fever on days 1 and 3 - 48 hours apart) = P. vivax and P. ovale (“benign”) and P. falciparum (“malignang”)

Quartan (fever on days 1 and 4 - 72 hours apart) = P. malariae

Question 16

General signs and sx of malaria

Answer 16

Fever - cyclical 
Hemolytic anemia 
Splenomegaly 
Jaundice 
Hemoglobinuria 
Tachycardia 
Hypotension / shock

Question 17

Malaria - Diagnosis

Answer 17

Blood smear shows trophozoite ring forms within RBCs

mAb detection of PfHRP2 is specific for P. falciparum

Question 18

Trypanosoma brucei - Pathogenesis

Answer 18

sub-species Rhodensiense (E. Africa) and Gambiense (W. Africa)

Infectious trypomastigote is injected into blood by Tsetse fly; initially causes a local chancre followed by parasitemia

Stage I: IgM immune complex deposition causes vasculitis (fever, rash, headache, lymphadenopathy)

Stage II: CNS involvement causes convulsions , somnolence, coma, and death

Question 19

Trypanosoma brucei - Treatment

Answer 19

Stage I: Suramin

Stage II: Eflornithine, Melasporol

Question 20

Trypanosoma cruzii - Pathogenesis & Presentation

Answer 20

Infective trapanomastigote passed by bite of Reduviid (“kissing”) bug causing an indurated lesion (chagoma)

Trypanomastigotes spread to lymphatics and blood, causing acute phase of fever, lymphadenopathy, and hepatosplenomegaly followed by late dilated cardiomyopathy, thromboembolism

Question 21

Trypanosoma cruzii - Diagnosis / specific signs

Answer 21

Giemsa stain

Romana’s sign - periorbital edema

Question 22

Leishmaniasis - Pathogenesis & Diagnosis

Answer 22

Transmitted of promastigote by sandfly bite; promastigotes activate complement and become phagocytosed; multiplication within phagocytes allows spread and invasion

Diagnosed by macrophages containing amastigotes

Question 23

Leishmaniasis - Clinical Presentation and Treatment

Answer 23

Cutaneous - ulceration

Mucocutaneous - erosion of nasal septum / palate

Visceral - disseminated disease; presents with fever, diarrhea, hepatosplenomegaly, ascites, hyperpigmentation of skin, death

Treatment: Sodium stibogluconate, Amphotericin B

Question 24

Toxoplasmosis - Pathogenesis and Presentation

Answer 24

Ingestion of bradyzoites in cysts via contaminated / under-cooked meat, cat feces; vertical transmission also occurs

Presents with acute, mononucleosis-like illness + brain abscess

Question 25

Toxoplasmosis - Vertical transmission patterns

Answer 25

1st trimester - Vertical transmission is 15% but disease is more severe (chorioretinitis, hydrocephalus, intracranial calcification)

3rd trimester - Vertical transmission is 65% but neonatal disease is less severe; infant likely to be asymptomatic at birth with later neurological sequelae

Question 26

Toxoplasmosis - Diagnosis and Treatment

Answer 26

Serology
Biopsy of tissue shows cysts containing bradyzoites
Brain MRI shows ring-enhancing lesion

Treatment: Pyrimethamine + Sulfadiazine