Parasitology Flashcards
PARASITISM
a symbiotic relationship
in which one animal,
the parasite, lives at
the expense of the
other animal, the host
Mutualism - both species benefits
Commensalism - A benefits, B unaffected
Parasitism - A benefits, B harmed
TYPES
OF
PARASITE
Based on Host Dependency
• Obligate Parasite – cannot survive
without a host
• Facultative Parasite – has free-living
forms or can act as commensal
Based on Location on the Host
• Endoparasite – within the host; infection
• Ectoparasite – the surface of the host;
infestation
Based on Organism
• Protozoa
• Helminth
Definitive/
Primary
Host
• where the adult parasite lives and undergoes
sexual reproduction
• obligatory to life cycle
Intermediate
/ Secondary
Host
• where the larval stage lives and undergoes
asexual reproduction
• obligatory to life cycle
• can transmit parasite to definitive host
Paratenic/
Transport/
Carrier Host
• where the larval stage lives w/o further
development
• not obligatory to life cycle
• can transmit parasite to definitive host
Reservoir/
Temporary
Host
• additional source of infection
• not obligatory to life cycle
• can transmit parasite to definitive host
Accidental/
Dead-End
Host
• accidentally harbors the parasite
• cannot transmit parasite to definitive host
STAGES
OF
PARASITE
Infective Stage • stage at which the parasite
is detected in a specimen
from a host
PROTOZOA
“first animals”
unicellular eukaryotes
inhabit water and soil
taxonomic grouping is an ongoing process and in a state of flux
AMEBAE
use pseudopodia (“falls feet”, extensions of
cytoplasm) or protoplasmic flow for
movement
Members
Entamoeba sp.
Naegleria fowleri
Acanthamoeba castellani
Balamuthia mandrillaris
FLAGELLATES
use flagella for movement
Members
Giardia lamblia
Trichomonas vaginalis
Trypanosoma sp.
Leishmania sp.
Giardia intestinales
Has 8 flagella and ventral sucker disk that the parasite attaches itself to the intestines
3um
Trichomonas vaginalis
Flagellate causes urinary and genital tract infection
Has small undulating membrane
Does not have a cyst stage
CILIATES
use cilia for movement; denucleated
Member
Balantidium coli
APICOMPLEXA
nonmotile
complex life cycle, alternating between sexual and asexual
reproductive stages
intracellular parasites
Members
Cryptosporidium sp.
Cyclospora sp.
Toxoplasma gondii
Plasmodium sp.
Babesia microti
PROTOZOAN
REPRODUCTION:
ASEXUAL
Binary Fission
Budding
Schizogony
• multiple fission
• formation of many nuclei →
concentration cytoplasm
around each nucleus →
separation into daughter cells
PROTOZOAN
REPRODUCTION:
SEXUAL
Conjugation
• fusion of two cells
• migration of haploid nucleus (the
micronucleus) from each cell to
the other cell → fusion of haploid
micronuclei → division of fertilized
parent cells → daughter cells with
recombined DNA
Gametogony
• production of haploid gametes
(gametocytes) → fusion to a
diploid zygote
PROTOZOAN
STAGES
Trophozoite
• dormant, resistant, and usually
infectious form
• Oocyst – reproductive
structure formed by members
of Apicomplexa
Giardia lamblia
a.k.a. G. duodenalis, G. intestinalis
intestinal flagellate
the only common pathogenic protozoan found in the
duodenum and jejunum of humans
Trophozoite:
“old man’s eyeglasses” – leaf/heart-shaped
organism, has four pairs of flagella
large concave sucking disk on the ventral surface
Cyst:
encysts in the colon and passed in the stool
ellipsoid, thick-walled, highly resistant
two nuclei in immature forms and four nuclei in
mature cysts
Disease: Giardiasis
irritation and low-grade inflammation of the duodenal or
jejunal mucosa
acute or chronic diarrhea associated with crypt
hypertrophy, villous atrophy or flattening, and epithelial
cell damage
watery, semisolid, greasy, bulky, and foul-smelling stools
malaise, weakness, weight loss, abdominal cramps,
distention, and flatulence
H2S odor in stool or breath
Transmission: ingestion of cyst (contaminated water/food)
excysts in the duodenum
Diagnosis: enterotest/duodenal capsule/string test or
stool exam
Entamoeba histolytica
intestinal and tissue ameba
Trophozoite:
the only form present in tissues
2 zones:
hyaline outer margin
granular inner region that may contain RBCs
(pathognomonic)
Cyst:
glycogen vacuole and chromatoid bodies (masses of
ribonucleoprotein) with rounded ends (unlike splinter
chromatoidals in E. coli) → 4 nuclei w/
disappearance of chromatoid bodies & glycogen
vacuoles
Disease: Amebiasis
Intestinal Amebiasis
diarrhea, abdominal cramps, N/V, tenesmus
general discomfort, loss of appetite, weight loss, general malaise
Amebic Dysentery – severe; abdominal tenderness, fulminating dysentery, dehydration,
incapacitation
ameboma – granulomatous mass that is sometimes formed
Extraintestinal Amebiasis – via metastasis; rarely by direct extension
Liver Abscess/Amebic Hepatitis (most common)
progressive, nonsuppurative (unless secondarily infected), destructive w/o compression,
formation of a wall
surgical drainage – “anchovy paste”
Pulmonary Amebiasis
Other Extraintestinal Foci (e.g., brain, spleen, etc)
Entamoeba histolytica
T: ingestion of cyst (contaminated
water/food)
excysts in the colon
Pathology:
flask-shaped ulcer
pinhead-sized center and raised edges, from w/c
mucus, necrotic cells, and amebae pass
Dx: cyst or trophozoites with ingested RBCs
in stool exam
OTHER
INTESTINAL
AMEBAE
E. dispar
• not a symbiont
E. moshkovskii
• small, nonpathogenic
E. hartmanni
• nonpathogenic
E. coli
Iodamoeba bütschlii
Endolimax nana
Diaentamoeba fragilis (a flagellate)
Cryptosporidium hominis,
Cryptosporidium parvum
intestinal sporozoan
infect the immunocompromised (e.g., AIDS)
Disease: Cryptosporidiosis
severe, intractable watery diarrhea
self-limited in immunocompetent hosts
T: ingestion of sporulated oocyst (contaminated
water/food)
excysts in the small intestine
D: oocysts in stool exam w/ acid-fast stain
Cyclospora cayetanensis
intestinal sporozoan
Disease: Cyclosporiasis
self-limited diarrhea, anorexia, fatigue, weight loss in
immunocompetent hosts
prolonged in immunocompromised (e.g., AIDS)
T: ingestion of oocysts (contaminated water/food
[fresh produce])
take days or weeks to become infectious
D: oocysts in stool exam w/ acid-fast stain
Cystoisospora belli
previously called Isospora belli
intestinal sporozoan
predominantly an infection of people in the developing world
and a common presentation of HIV/AIDS
Disease: Cystoisosporiasis
Immunocompetent:
self-limited
sudden, nonbloody, watery diarrhea, with fever, abdominal cramps, nausea, anorexia, and
malaise
Immunocompromised:
prolonged illness
severe, intractable, voluminous diarrhea, and weight loss resembling cryptosporidiosis
Transmission: ingestion of non-sporulated
oocysts
excyst in small intestine
Diagnosis: oocysts in stool exam w/ acid-
fast stain
Balantidium coli
the only ciliate protozoan parasite of humans
the largest protozoan parasite of humans
CF: Balantidiasis
usually asymptomatic
mucosal ulcers and submucosal abscesses, resembling lesions in
amebiasis
does not invade extra intestinal sites
T: ingestion of cyst in contaminated food or water
Trichomonas vaginalis
SEXUALLY TRANSMITTED
PROTOZOA
genitourinary flagellate
anaerobic
Disease: Trichomoniasis
usually asymptomatic or mild
Women: more common
mucosal surfaces may be
tender, inflamed, eroded
frothy yellow or cream-colored
discharge
local tenderness, vulvar
pruritus, burning
limited to the vulva, vagina,
and cervix
Men: less common
infect the prostate, seminal
vesicles, and urethra
T: trophozoites passed via sexual
intercourse
no cyst stage
Trypanosoma brucei
Disease: African Trypanosomiasis
Cutaneous Stage:
chancre at inoculation site
Hemolymphatic Stage:
intermittent fever, headaches, rigors, muscle and joint pain
generalized lymphadenopathy
Winterbottom sign (enlarged lymph nodes in the posterior cervical triangle w/ T. b.
gambiense)
CNS Stage:
headache, inability to concentrate, personality changes (e.g., progressive lassitude and
indifference), daytime somnolence, tremor, ataxia
terminal coma
death (w/n months for acute and within 2-3 yrs for chronic)
Transmission: inoculation of
metacyclic trypomastigotes by
tsetse fly
Diagnosis: trypomastigotes
(extracellular) in blood smear,
bone marrow, CSF
elongated bodies supporting a
longitudinal lateral undulating
membrane
a flagellum that borders the free
edge of the membrane and
emerges at the anterior end as a
whip-like extension
Trypanosoma cruzi
Disease: Chagas Disease
Acute:
Chagoma – subcutaneous inflammatory
nodule at the site of inoculation
Romaña sign – unilateral swelling of the
eyelids
fever, acute regional lymphadenitis, and
dissemination to blood and tissues
Chronic:
Heart: chagasic cardiomyopathy associated
with fibrosis in response to the presence of
intracellular parasites in heart tissue;
arrhythmia
GIT parasympathetic ganglia: megacolon,
megaesophagus
Transmission: inoculation of metacyclic
trypomastigotes in the feces of reduviid
bugs
Diagnosis:
trypomastigotes (extracellular) in blood smear,
bone marrow, CSF
amastigotes (intracellular) in tissue biopsy
CUTANEOUS
LEISHMANIASIS
small, red papule → rolled-edge ulceration
→ depressed, unpigmented scar
MUCOCUTANEOUS
LEISHMANIASIS
small, red papule → itchy, ulcerated vesicle →
degeneration of cartilaginous and soft tissues
in nasal and buccal mucosa (erosion)
VISCERAL
LEISHMANIASIS
low-grade fever, malaise → progressive
wasting and anemia →
hepatosplenomegaly → death due to
secondary infection
post-kala-azar dermal leishmanoid –
reddish, depigmented nodules
Leishmania
Transmission:
inoculation of
promastigote by sandfly
Diagnosis: amastigotes (intracellular)
biopsy
Naegleria fowleri
a.k.a. N. aerobia
free-living ameba; an ameboflagellate
Disease: Primary Amebic
Meningoencephalitis (PAM)
acute, fulminant, rapidly fatal illness
headache, fever, lethargy, rhinitis, N/V, and
disorientation due to extensive hemorrhage
and damage in brain tissue
Transmission:
swimming in warm freshwater
entry of flagellated trophozoites via the nose
and the cribriform plate of the ethmoid bone to
the brain
Diagnosis: trophozoites in CSF and brain tissues
