PROTOZOA

Question 0

Parasite biology:

• pseudopod-forming nonflagellated protozoa –> BROWNIAN MOVEMENT
• most invasive parasite among Entamoeba
• Eukaryotic organism that lacks membrane-bound organelles

Transmission: fecal oral route

Infective stage: mature cysts

Diagnostic stage: trophozoites, mature cysts, immature cysts

Pathogenesis: VIRULENCE FACTORS

• LECTIN mediates adherence
• AMEBAPORES for penetration
• CYSTEINE PROTEASES for cytopathic effect

Spectrum of disease:

• cyst carrier state
• amebic colitis (dysentery without fever, flask-shaped colon ulcers
• ameboma (associated with dysentery)
• amebic liver abscess (most common extraintestinal form, anchovy-like aspirate)

Treatment:

• cyst carrier state (Diloxanide furoate)
• amebic colitis (Metronidazole)
• amebic liver abscess (Metronidazole, percutaneous drainage for nonresponders)c

Answer 0

Entamoeba histolytica

Question 1

Parasite biology:

• flagellate that lives in the duodenum, jejunum and upper ileum
• falling-leaf motility
• simple asexual life cycle
• covered with variant surface proteins

Transmission: fecal-oral route

Infective stage: cysts

Diagnostic stage: trophozoites, cysts

Pathogenesis:

• adhesive disc and lectin facilitate attachment to avoid peristalsis
• villous flattening, crypt hypertrophy and discruption of cytoskeleton
• ultimately leads to enterocyte apoptosis

Spectrum of disease:

1. Acute infection - abdominal pain, diarrhea and excessive flatus, smelling like rotten eggs
2. Chronic infection - constipation, weight loss and steatorrhea

TX: Metronidazole

Answer 1

Giardia lamblia

Question 2

Parasite biology:

• opportunistic intestinal protozoa
• undergoes schizogony and gametogony
• autoinfection in immunocompromised patients
• acid-fast organism

Transmission: fecal oral route

Infective and Diagnostic stage: thick-walled oocysts

Spectrum of disease:

• self limited nonbloody diarrhea
• severe life-threatening diarrhea if CD

Answer 2

Cryptosporidium parvum

Question 3

Parasite biology:

• Urogenital protozoan
• exists only as a trophozoite
• pear shaped, flagellated trophozoites

Transmission: sexual intercourse, “ping-pong” transmission

Infective and Diagnostic stage: trophozoites

Spectrum of disease: TRICHOMONIASIS

• watery, foul-smelling, greenish vaginal discharge accompanied by itching and burning
• strawberry cervix

TX: single oral dose of 2 grams (four 500mg tablets) of Metronidazole

Answer 3

Trichomonas Vaginalis

Question 4

Parasite biology:

• blood and tissue sporozoa
• most important parasitic disease in man
• asexual life cycle consists of schizogony and gametogony
• sexual life cycle involves sporogony

Transmission: bite of infected female mosquito (Anopheles)

Infective stage: sporozoites

Diagnostic stage: trophozoites (ring form)

Pathogenesis:

• pathologic findings from the destruction of red blood cells (release of the merozoites and splenic sequestration of infected cells)
• people with RBC defects (G6PD, sickle cell) are immune to malaria
• partial immunity (premonition) seen in individuals who completely recover from falciparum malaria

Special clinical outcomes:

1. Recrudescence - recurrence of symptoms after a temporary abatement (2-4 weeks); seen in P. Falciparum and P. Malariae
2. Relapse - return of a disease after its apparent cessation (1-6 mos) due to reactivation of hypnozoites; seen in P. Ovale and P. Vivax

Diagnosis:

• thin and thick smears with Giemsa stain (thick smear to screen for the presence of organisms; thin smear for species identification)
• highest yield when blood samples taken during fever or 2-3 hours after peak

Malarial dots:

1. SCHUFFNER DOTS - punctuate granulations present in red blood cells invaded by P. Ovale and P. Vivax
2. MAURER DOTS - coarse granulations present in red blood cells invaded by P. Falciparum
3. ZIEMANN DOTS - fine dots present in red blood cells invaded by P. Malariae

Spectrum of disease:

• paroxysmal fever with malaise and bone pains
• hemolytic anemia, jaundice and splenomegaly
• parasitic pneumonitis
• cerebral malaria (malarial or Durck granulomas)
• acute renal failure (Blackwater fever) (severe complication of P. Falciparum malaria, characterized by intravascular hemolysis, massive hemoglobinuria and acute renal failure, rare and sometimes fatal complication in quinine-sensitized persons)
• septic shock (Algid malaria)

Local epidemiology:

1. AREAS OF HIGH ENDEMICITY - Palawan, Kalinga-Apauao, Ifugao, Agusan del sur
2. AREAS OF CHLOROQUINE-RESISTANCE - Palawan, Davao del Norte, Compostela Valley

TX:

1. TISSUE SCHIZONTICIDES - kill schizonts in the liver, example ( primaquine)
2. BLOOD SCHIZONTICIDES - kill these parasitic forms only in the erythrocyte, example (chloroquine, quinine)
3. GAMETOCIDES - kill gametocytes in human blood,example (primaquine)
4. SPORONTICIDES - prevent sporogony and multiplication in the mosquito, example (proguanil, pyrimethamine)

Treatment: Special Situations

1. Chloroquine-resistance - Mefloquine+doxycycline
2. Eradication of hypnozoites - Primaquine
3. Severe cases or pregnant - Quinidine or Quinine

• for CHLOROQUINE-SENSITIVE areas: CHLOROQUINE 500mg/tab, 1 tab weekly
• for CHLOROQUINE-RESISTANT areas: MEFLOQUINE 250mg/tab, 1 tab weekly, MALARONE (Atovaquone 250mg / Proguanil 100mg/tab, 1 tab daily)
• for MULTIDRUG-RESISTANT areas: DOXYCYCLINE 100mg/tab, 1 tab daily

Prevention:

• chemoprophylaxis
• insecticide-treated nets
• insect repellants with DEET
• biological modification –> cultivation of snails that eat up mosquito larvae

Answer 4

Plasmodium

Question 5

Parasite biology:

• tissue protozoan
• definitive host is the domestic cat
• humans and other mammals are intermediate hosts

Transmission: ingestion of cysts in raw meat, contaminated food, transplacentally

Infective stage: fecal oocysts

Diagnostic stage: trophozoite (bradyzoites)

Pathogenesis:

• 2 types of trophozoites (rapidly multiplying tachyzoites- CMI limits spread, slowly multiplying bradyzoites- important in tissue diagnosis)
• preferred diagnostic test: IgM antibody

Spectrum of disease:

1. Immunocompetent - heterophil-negative mononucleosis
2. Immunocompromised - encephalitis (ring enhancing lesions)
3. Congenital toxoplasmosis - abortion, stillbirth, or neonatal disease with hydrocephalus, encephalitis, chorioretinitis and heoatosplenomegaly (intracranial calcifications)

TX: sulfadiazine plus pyrimethamine

Answer 5

Toxoplasma Gondii

Question 6

Parasite biology:

• blood and tissue protozoan
• all 4 forms: amastigote, promastigote, epimastigote, trypomastigote
• transmitted by reduviid bug

Transmission: reduviid bug (Triatoma) bite

Infective stage: Metacyclic trypomastigote

Diagnostic stage: trypomastigotes in blood

Pathogenesis:

• myocardial, glial, and reticuloendothelial cells are frequent sites
• cardiac muscle is the most frequently and severely affected tissue

Diagnosis:

• stained BMA or muscle biopsy
• culture of the organism on special medium
• xenodiagnosis (allowing an uninfected, laboratory-raised reduviid bug to feed on the patient)

Spectrum of disease:

1. Acute Chaga’s disease - periorbital edema (Romana’s sign), nodule near bite (chagoma), fever, LAD, and heoatosplenomegaly
2. Chronic disease - myocarditis, megacolon, megaesophagus (achalasia)

TX: Nifurtrimox

Answer 6

Trypanosoma Cruzi

Question 7

Parasite biology:

• blood and tissue protozoan
• only 2 forms: epimastigote, trypomastigote
• remarkable antigenic variation
• 2 members: Trypanosoma Brucei gambiense, Trypanosoma Brucei rhodesiense

Transmission: tsetse fly (Glossina) bite

Infective stage: Metacyclic trypomastigotes

Diagnostic stage: trypomastigotes in blood

Pathogenesis:

• spread from the skin through the blood to the lymph nodes and the brain
• somnolence (sleeping sickness) progresses to coma due to demyelinating encephalitis (ARAS, brainstem)
• cyclical fever spike (every 2 weeks) due to antigenic variation
• Rhodesian more rapid and fatal than Gambian

Spectrum of disease:

• indurated skin ulcer (trypanosomal chancre)
• intermittent weekly fever and LAD
• enlargement of the posterior cervical LN (Winterbottom’s sign)
• excessive somnolence
• hyperesthesia (Kerandel’s sign)
• encephalitis - plasma cells with cytoplasmic immunoglobulin globules (Mott cells)

TX: Suramin for blood-borne disease, Melarsoprol for CNS penetration

Answer 7

Trypanosoma Brucei

Question 8

Characteristics:

• flagellated marine protists
• algal blooms cause red tide
• most common cause in the Philippines is PYRODINIUM BAHAMENSE VAR. COMPRESSUM

Transmission and pathogenesis:

• transmission by eating bivalve mollusks (mussels, clams, oysters and scallops) and fish obtained from red tide
• filter feeders accumulate toxins produced by dinoflagellates

TX:

• gastric lavage with activated charcoal
• supportive fluid resuscitation
• endotracheal intubation for respiratory failure
• neostigmine and edrophonium to improve muscle weakness

Answer 8

Dinoflagellates

Question 9

Granulomatous amebic encephalitis

- Free-living ameba

Answer 9

Acanthamoeba castellanii

Question 10

Primary amebic meningoencephalitis

• free-living ameba
• acquired while swimming in contaminated pools

Answer 10

Naegleria fowleri

Question 11

Only ciliate protozoan to cause human disease

Associated with pigs

Round-based, wide-necked intestinal ulcers

Answer 11

Balantidial dysentery (Balantidium coli)

Question 12

Transmitted by the bite of the Ixodes tick

Intra erythrocytes ring-shaped trophozoites in tetrads in the form of Maltese cross

Answer 12

Babesiosis (Babesia microti)

Question 13

Transmitted by sandfly

Infective promastigotes

Spectrum of disease:

• CUTANEOUS: Leishmania tropica
• VISCERAL/KALA-AZAR: Leishmania donovani
• MUCOCUTANEOUS: Leishmania braziliensis

DOC: Sodium steno gluconase

Answer 13

Leishmaniasis

Question 14

Coccidial sporozoa

Cause diarrhea in immunocompromised patients

Answer 14

CYCLOSPORA CAYETANENSIS & ISOSPORA BELLI