Parasitology MDL 236 Fall 05

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Parasitology MDL 236Fall 05
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Why they pay you per McKay

• Assist health care provider diagnose parasitic
  infections
• Explain specimen collection procedures to
• health care personnel and patients
• Discuss lab results with health care personnel
• YOU are the expert!
• ?

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Why they pay you per McKay
More specifically, detect and identify protozoal
trophozoites cysts, and helminth adult worms,
larvae eggs in clinical specimens using
microscopic and gross macroscopic examinations.
The majority of the parasitic infections in
industrialized countries are intestinal therefore
most lab examinations are on feces. Blood,
urine, sputum and various body fluids or tissue
biopsies are occasionally examined.
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Parasitology
What is a parasite? Symbiosis
mutualism commensalism
? parasitism Which critters are we
talking about here? 1) Protozoans 4-6
phyla? see info to come
important stages in life cycle?
trophozoite active feeding reproduction
cyst dormant, resiliant stage
Plasmodium several important
stages 2) Helminths flukes
(Trematodes) tapeworms (Cestodes)
roundworms (Nematodes)
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Prevalence of parasitic infections
See page 1071 See Box 20-1, page 1072 Read the
1st few paragraphs of this link http//gsbs.utmb
.edu/microbook/intopara.htm Activities can
predispose infection Immune compromised
individuals at high risk America is the place to
be On-line data Centers for Disease Control
World Health Organization
Computerized Patient Care Network
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Risk and prevention pg 1074
Stay in the U.S.!!! If traveling
1.limit exposure to areas with poor
infrastructure 2.avoid parasites in food water
water drink, ice, food, shower, tooth
brushing food cook food thoroughly
fresh fruits vegies -
wash water? 3.avoid insect bites 4.chemoprophyla
ctic drugs vs malaria

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Clinical manifestations pg 1074
These examples illustrate that parasites differ
pathologically as well as morphologically. We
will cover these later. Intestinal parasites
diarrhea blood /or mucus
intestinal cramping

bowel obstruction ex. Ascaris
weight loss ex. Taenia
Hemoflagellates ex. Trypanosomes, Plasmodium
fever edema, vasculitis, etc.
cardiac
tachycardia, enlargement, carditis CNS
headache, encephalitis superinfections -
shock weight loss ?
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Clinical manifestations continued
Leismaniasis superinfections-shock
wasting cutaneous lesions of skin / mucous
membrane visceral hepatomegaly
splenomegaly
anemia Helminths
elevated eosinophil count and lots more!
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Specimen collection processing pg 1075
Parasite detection ID relies solely on
macroscopic microscopic examination. Success
depends upon samples containing organisms intact
and with normal characteristic morphology. As
discussed earlier, the majority of patient
samples are fecal. Other samples include urine,
blood, sputum and various tissues. Being
wall-less, parasites are susceptible to
dessication osmotic instability. Proper
osmolarity must be maintained during sampling
preservation define tonicity terms,
plasmolysis, plasmoptysis ? sampling, prep,
diagnostic procedures lab?
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Fecal specimen collection processing see 1075
Goal maximize probability of detection
ID 1.Avoid sample dilution, amendment or freezing
vs trophozoite plasmoptysis 2.Avoid in vivo
contamination from meds/substances that can alter
parasite morphology get sample before or you
must wait 3.Sample collection on successive days
may be necessary to see cyst germination ?
trophozoites 4.Prompt direct examination of stool
samples is necessary due to instability of
trophozoites. See book 30 mins. to 1
day. 5.Dont shoot in the dark
formed stool
samples are unlikely to contain trophozoites
focus search on heterogenous spots blood,
mucus, other
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Diagnostic procedures pg 1076

• Microscopic examination methods
• 1. a)Direct (not preserved) wet mounts NO
  stain
• mix sample with saline, apply coverslip(?),
  view under low power helminths or high dry
  (protozoans)
• Points to consider about direct wet mounts
• parasite trophs die quickly outside the body
  be prompt
• only method for determining motility - all
  parasites
• ideal for detecting/ID of helminth worms,
  larvae eggs
• inferior for ID of protozoa (except maybe
  Giardia?)
• best for heavy infections, otherwise may go
  unnoticed
• physiological saline osmotic stability
• transparent low contrast harder to see
• fast may need protoslo, etc.
• not too thick BUT not too thin...depends on
  sample type ?

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Diagnostic procedures continued
Microscopic examination methods continued 1. b)
Direct wet mounts - temporary wet stains
adding dye to wet mount to add contrast
1. iodine - binds polysaccharides
good for internal structures -
organelles 2. buffered methylene blue
binds acidic / (-) charges This includes most
parts of the cells / organism
images?