PROTOZOA Flashcards
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
Entamoeba histolytica
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:
- Acute infection - abdominal pain, diarrhea and excessive flatus, smelling like rotten eggs
- Chronic infection - constipation, weight loss and steatorrhea
TX: Metronidazole
Giardia lamblia
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
Cryptosporidium parvum
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
Trichomonas Vaginalis
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:
- Recrudescence - recurrence of symptoms after a temporary abatement (2-4 weeks); seen in P. Falciparum and P. Malariae
- 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:
- SCHUFFNER DOTS - punctuate granulations present in red blood cells invaded by P. Ovale and P. Vivax
- MAURER DOTS - coarse granulations present in red blood cells invaded by P. Falciparum
- 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:
- AREAS OF HIGH ENDEMICITY - Palawan, Kalinga-Apauao, Ifugao, Agusan del sur
- AREAS OF CHLOROQUINE-RESISTANCE - Palawan, Davao del Norte, Compostela Valley
TX:
- TISSUE SCHIZONTICIDES - kill schizonts in the liver, example ( primaquine)
- BLOOD SCHIZONTICIDES - kill these parasitic forms only in the erythrocyte, example (chloroquine, quinine)
- GAMETOCIDES - kill gametocytes in human blood,example (primaquine)
- SPORONTICIDES - prevent sporogony and multiplication in the mosquito, example (proguanil, pyrimethamine)
Treatment: Special Situations
- Chloroquine-resistance - Mefloquine+doxycycline
- Eradication of hypnozoites - Primaquine
- 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
Plasmodium
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:
- Immunocompetent - heterophil-negative mononucleosis
- Immunocompromised - encephalitis (ring enhancing lesions)
- Congenital toxoplasmosis - abortion, stillbirth, or neonatal disease with hydrocephalus, encephalitis, chorioretinitis and heoatosplenomegaly (intracranial calcifications)
TX: sulfadiazine plus pyrimethamine
Toxoplasma Gondii
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:
- Acute Chaga’s disease - periorbital edema (Romana’s sign), nodule near bite (chagoma), fever, LAD, and heoatosplenomegaly
- Chronic disease - myocarditis, megacolon, megaesophagus (achalasia)
TX: Nifurtrimox
Trypanosoma Cruzi
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
Trypanosoma Brucei
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
Dinoflagellates
Granulomatous amebic encephalitis
- Free-living ameba
Acanthamoeba castellanii
Primary amebic meningoencephalitis
- free-living ameba
- acquired while swimming in contaminated pools
Naegleria fowleri
Only ciliate protozoan to cause human disease
Associated with pigs
Round-based, wide-necked intestinal ulcers
Balantidial dysentery (Balantidium coli)
Transmitted by the bite of the Ixodes tick
Intra erythrocytes ring-shaped trophozoites in tetrads in the form of Maltese cross
Babesiosis (Babesia microti)
Transmitted by sandfly
Infective promastigotes
Spectrum of disease:
- CUTANEOUS: Leishmania tropica
- VISCERAL/KALA-AZAR: Leishmania donovani
- MUCOCUTANEOUS: Leishmania braziliensis
DOC: Sodium steno gluconase
Leishmaniasis
Coccidial sporozoa
Cause diarrhea in immunocompromised patients
CYCLOSPORA CAYETANENSIS & ISOSPORA BELLI
