Parasitology Exam 1 study guide.docx - Parasitology Exam 1...

Parasitology Exam 1 study guide
E Protozoa
 General Characteristics of Protozoa
o Single celled Eukaryotic organisms
o 1 nucleus
o motile
o Only a small fraction are parasitic in man
o Gain entry to hosts 3 ways:
 Orally
 Vector
 Sexual transmission
 Reproduction in Protozoa
o General rule: asexual in host
o Asexual:
 Binary fission: one becomes two
 Multiple fission: one becomes many
 Schizogonoy
 Merogony
 Gematogony  formation of gamets
o Sexual: fusion of gametes (Syngamy)  zygote
 Severity of Parasitic Disease:
o Size of infective dose
o Immune status of host
Amoebas + Ciliates
 Morphology
o Trophozoite – single cell, feeding + reproducing form
o Cyst – infective stage for new host, environmentally resistant form
 Transmission
o Direct life cycle
o Cyst ingested by host
 Reproduction – binary fission
Entamoeba (genus)
 E. histolytica - pathogen
 E. dispar – commensal
 E. coli – commensal
 E. hartmanni – commensal
 E. gingivalis – commensal
E. histolytica
 Worldwide, trophozoite (motile, feeds on host cell), cyst (4 nuclei, infective stage)
 Host niche: large intestine and rectum

 Transmission: ingestion of cyst
 Clinical classification – amoebas
o Intestinal amoebas
 Asymptomatic carrier
 Diarrhea
 Dysentery
 Chronic
 Asymptomatic carriers
o No clinical signs (trophozoites rapidly form cysts)
o A source of infection for others (carriers shed infective cysts)
 Intestinal amebiasis – amebic colitis
o Diarrhea – clinical sign
o Acute amebic colitis (one or more days of diarrhea)
o Pathogenesis
1. amoeba attaches to surface of mucosal cells of large intestine
2. lyses cell
3. invades
4. ulcerates
5. ulcers
 amebic dysentery
o dysentery (bloody, mucoid diarrhea)
o tender abdomen
o trophozoites only seen on feces
o severe bleeding into the gut lumen + sloughing of gut mucosa
 chronic amebic colitis
o recurrent bouts of diarrhea (no dysentery)
o abdominal pain
o trophs + cysts in stool
o mucosal ulcerations
o complications – gut perforation, ameboma (mass in large intestine composed of
trophozoites, WBC, and cellular debris)
 extraintestinal amebiasis
o dead end journey for parasite
o trophozoites only, no cysts
o hepatic: liver abscesses (most common site)
o pulmonary: lung abscesses
o cutaneous: skin abscesses
o cerebral: brain abscesses
differential diseases – diseases with similar symptoms
 cutaneous amebiasis – perforation of amebic ulcer which adhere to abdominal wall
Dx

 intestinal
o microscopy
 stained fecal smear
 tissue biopsies
 stool antigen detection – rapid + reliable
 extra intestinal
o serological test – ELISA
o scans (CT, rads) – fine needle biopsy of large liver abscess or any abscess resisted
to antibiotics
Rx
 asymptomatic
o