[Protzoans]
TerminologyDefinitive hostHost that harbors adult stage of a
helminth or sexual stages of a protozoanIntermediate hostHost that
harbors the larval stage of a helminth or ASEXUAL stages of a
protozoanReservoir hostVertebrae animal, usually other than
humanHarbors a parasitePotential source of infection to
humansZoonosisDisease of lower vertebrates that is transmissible to
humans
Dx & TxMicroscopyFecal samples (O&P)Usage: intestinal
parasitesProtozoa: Cryptosporidium, Entamoeba, GiardiaHelminth
(eggs): Ascaris, Trichuris, Hookworms, Flukes (Schistosomes), some
tapewormsHelminths (adults): Strongyloides, some
tapewormsCollection & preservationFecal samples should be
transported & examined by lab w/i 30 mins 2 hrsIf cant, need
preservatives! 10% formalinPolyvinyl alcoholNa
acetate-formalinConcentrationSeparate eggs from other fecal
materialMethods:Zinc sulfate floatationFormalin-ethyl acetate
sedimentationMicroscopic examinationWet mountsStool samples diluted
w/ normal salineStainsIncreases contract, improves detection,
prepares permanent slides for archival purposesExamples:Trichome
& Giemsa (works for most parasites)IodineModified acid-fastGood
for Crypto!Iron hematoxylinCalcofluor white
Ag-detection kits Abs to major parasite Ags can be used with
high sensitivityELISA, Western blotting, immunofluorescence
microscopyPerianal specimensGood for PINWORMS! (Enterobius)Clear
cellophane tape to perianal folds microscope slide see eggs on
tapeDone in morning, before bathingIntestinal sampling
Sigmoidoscopy/EndoscopyUsed if fecal method cannot confirmSample
from multiple sitesSigmoidoscopy: good for Entamoeba
histolyticaEndoscopy of duodenum: good for Strongyloides, Giardia,
CryptosporidiumUrogenital Urine, vaginal, prostatic secretionsGood
for Trichomonas vaginalis, SchistosomesBlood filmsGood for malaria,
trypanosomiasis, fliariasis, leishmaniasisThin & thick
filmsOtherCSF: Naegleria, ToxoplasmaLiver abcess bx: EntamoebaLymph
node bx: Toxoplasma, LeishmaniaMuscle bx: Trichinella
ImmunodiagnosticsPresence of Ab in serumTested by EIAUnable to
distinguish b/t acute vs. chronic vs. recently clearedPresence of
Ag in serumTested by EIARequires a lot of materialMore indicative
of acute infxn than Ab testImmunofluorescenceUses
fluorescently-labeled Abs on fecal samplesGood for intestinal
parasiteIncreased visibility improves detectionMolecular approaches
Detection of parasite nucleic acids via PCRHigh specificity &
sensitivityCultureNOT USEFUL for most parasites (diff. from fungal
& bacterial!)No immunization available for parasitesImproved
sanitation & control of vectors/intermediate hosts best
approach
Protozoan Parasites Single-celled
Intestinal ProtozoaStages:TrophozoiteCause
pathologyCystsInvolved in
transmissionTransmissionFecal-oralContaminated drinking
waterClose-contact settingsDaycareHospitalDo not have intermediate
hostsSome found in animalsLife cycle
Infection vs. carriageAsx carriage w/ eventual clearance:
50%+Children, elderly, immunocompromised more likely be to be
symptomatic
Endemic Extraintestinal ProtozoaVector transmission & tissue
tropismNOT transmitted by vectors & do NOT have prominent
bloodstream phasePrimary infection site:Brain &
eyesTrichomonas, Naegleria, AcanthamoebaGU
tractTrichomonasGeographic rangeWorldwideToxoplasmosis &
trichmoniasis prevalent in US
Toxoplasma gondii
Non-endemic Extraintestinal ProtozoaTransmissionContact w/
intermediate hostArthropod hosts = vectorsPerson-person
transmission usually not possible (except: blood transfusions)Life
cyclesMore complex vs. intestinal protozoaDifferent stages of life
cycle occurring in different hostsImportant of public heath
measuresMost important: vector control through sanitation, draining
of insect breeding grounds, insecticide spraying
Extraintestinal protozoans (cont) & HelminthsExtraintestinal
protozoans
[Helminths]
I. Invertebrate worms are multi-cellular animals with complex
body plans
II. Characterization (by taxonomy & morphology)A.
Nematodesi. Roundworms1. Pinworms, roundworms, whipworms,
filariasisB. Trematodesi. Flatworms1. Intestinal or liver flukesC.
Cestodesi. Tapeworms1. Beef, fish, pork tapewormsa. Based on
intermediate hosts from which infection is acquired
III. Categorization (by anatomical site)A. Extraintestinal rare
group by taxonomy
IV. Life CyclesA. Developmental Stagesi. Most have egg, larval,
and adult stages1. Infectious forms almost always: larval or egg
stagesB. Hostsi. For most: human is host of adult stageii. Most
also have intermediate and/or reservoir hosts1. Intermediate hosts
frequently required for completion of life cycleC. Sexual cyclesi.
Generally have complete sexual cyclesii. Some spp. have bigender (M
& F) system, other are hermaphroditic
V. PathologyA. Characteristic of both bug & infection
site
VI. PreventionA. Transmissioni. Few: vector-borneii. Most:
fecal-oral routeB. Public health measures most important means of
controli. Adequate sanitationC. Several tapeworms acquired via
incompletely cooked meats or fish
A. Nematodesi. RULE: Sexual reproduction between M & F1.
Exception: Strongyloidesa. Parthenogenic (uniparental
development)
B. Trematodesi. Flukesii. Flat, leaf-shaped wormsiii. Most are
hermaphrodites1. Schistomsoma is bisexualiv. Definitive host =
humansv. Intermediate host = snails or freshwater fish1. Or water
plants in contact with snails2. Infections result from contact with
thesevi. Reservoir = Several mammals vii. Classified by anatomical
infection site1. Sx depends on particular site
C. Cestodesi. Characteristics1. Flat, segmented wormsa.
Segmentsi. Each contain complete sexual organs & can produce
fertile eggsii. Can detach from adult worm2. All are
hermaphrodites3. Hooklets & suckers on head (scolex) enable
attachment to hostii. Adult worms usually found in intestines &
generally toleratediii. Larval worms can be extraintestinal &
cause Sx based on tissue siteiv. Diagnosis1. Both proglottid
segments & eggs can be found in fecesv. Found worldwide
[Fungi]
I. Dimorphic FungiA. Generali. Pathogenic dimorphic fungis
phases regulated by temperature1. Saprophytic or environmental
phase (25C)a. Fungi grow as moulds2. Tissue or parasitic phase
(35-37C)a. Fungi grow as yeasts or yeast-likeb. NOT necc. component
of life cyclei. Adaptive response to altered growth environmentB.
Disease characteristicsi. Portal of entry is respiratory tract1.
Infection is acquired via inhalation on conidia produced by mold
phaseii. Tissue phase NOT transmissible 1. No person-to-person
spread of infectioniii. Primary infections most commonly occur in
respiratory tract1. Usually benign & self-limitingiv. Some
infected individuals will progress to serious pulmonary or even
disseminated disease with multi-organ involvement1. Extent of
disease is regulated by immunological response of hosta. Humoral
response (specific Ab)i. Minimal role in protectionii. May
sometimes increase disease severity (hypersensitivity rxns)iii.
Measurement of Ab titers is occasionally useful for diagnosis &
prognosisb. Cell-Mediated Responsei. T-cells, cytokines, activated
macrophagesii. Primary protective mechanism & major determinant
of disease severityv. Infections caused by different dimorphic
fungi are distributed in specific geographic locations1. Endemic
areas are a reflection of the environmental habitats of the mold
phase of these fungi
II. Opportunistic FungiA. Generali. More than 90% of fungal
infections occurring in hospitalized individuals 1. Most d/t
Candidaii. Ubiquitous & low virulence
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