MLSC 3333- Intro to Parasitology

carrier

Asymptomatic host that harbors a parasite and is capable of transmission to others

commensalism

Host-parasite relationship that is beneficial to one and harmless to another

definitive host

Required for adult or sexual phase of the parasite's life cycle

mutualism

beneficial to both host and parasite

parasite

any organism that obtains its nutrients from another organism (maybe be harmful, beneficial or neutral)

synbiosis

association between 2 organisms

zoonosis

-Animal parasitic infection that humans acquire as accidental hosts

-Typically humans do not get this parasite but due to accidental interaction with animal

cestodes

tapeworms

ciliates

motile protozoans

cyst

thick-walled stage of amoeba that is resistant to adverse conditions. Typically found in the environment

ectoparasite

external parasite (e.g. ticks and lice)

egg

oocyst, ovum, zygote

endoparasite

A parasite that lives within a host

filariae

blood or tissue roundworms requiring an insect vector for transmission

flagellates

protozoans with flagella

gravid

pregnant

helminths

includes nematodes (roundworms), cestodes (tapeworms) and trematodes (flukes).

hermaphroditic

tapeworms capable of self-fertilization. Both female and male sex organs

host

any living organism that harbors a parasite

hydatid cyst

Larval stage of Echinococcus granulosus

intermediate host

host containing the asexual phase of a parasite

larvae

juvenile stage of parasite

nematode

roundworm

oocyst

Encysted form of an egg

parasitic life cycle

stages in the development of a parasite; may require multiple hosts or specific nutrients

Parasitism

host-parasite relationship where one member benefits at the expense of the other

schizont

-Immature: early stage of asexual sporozoa trophozoite

-Mature: developed stage of asexual sporozoa trophozoite

trematodes

flukes

direct fluorescent antibody (DFA)

used to identify Trichomonas vaginalis

Direct agglutination test (DAT)

-Used to diagnose leishmaniasis and Chaga's disease

ELISA

Used to identify Toxoplasma gondii

complement fixation (CF)

-Used to diagnose leishmaniasis, Chaga's disease and pneumocyctosis

Gel diffusion precipitation (GFP)

detects amoebic infections

indirect immunofluorescent antibody

-Used to diagnose amoebic, malarial and schistosome infections and toxoplasmosis

Risk factors

Sanitation, Health state, transfusion/transplantation, transmission, travel

Infection characteristics

Diarrhea, Abdominal cramping, intestinal obstruction, weight loss, organ issues, bleeding/anemia, fever

How parasites are diagnosed

Life phase- ova, larvae, adult

Sample types

Stool, blood, tissue, spinal fluid, urine, sputum

What container is stool collected in?

Clean, Dry, Leakproof containers free of contaminants

How many stool samples can be collected? How often?

Up to 3, 1 every 24 hours

Macroscopic vs Microscopic Fecal exam

Macroscopic: Color, consistency, form

Microscopic: Staining, concentrate/direct exam

Antibiotics can lead to fecal samples being

red, purple, or blue in color

Gross abnormalities in macroscopic exam include

Adult worms, proglottids, pus, mucus

Consistency of Stool relation to parasite maturity

Eggs more common in formed stool, Trophs more common in watery stool

Time between passing and exam for liquid vs soft

Liquid- 30 mins

Soft- 1 hr

2 most common preservatives for stool samples

10% formalin and Polyvinyl Alcohol

What are some less common stool preservatives?

Merthiolate-iodine-formaldehyde (MIF), Sodium acetate-acetic acid-formalin (SAF), Schaudinns Fixative, one vial fixative

What is the ratio used for storing stool samples?

1 volume stool to 3 volumes preservative

Advantages of 10% formalin

All purpose fixative with long shelf life, preserves helminth eggs and larvae and protozoan cysts/coccidia, wide use range (concentrated procedures, acid fast/safranin stains, immunoassay)

Disadvantages of 10% formalin

Not suitable for trichrome stains, fails to preserve protozoan trophs, may interfere with PCR

Advantages of Polyvinyl Alcohol

Preserves protozoan cysts and trophs, Easy to prepare permanent stains like trichrome, creates samples with long shelf life

What is the main use for PVA

trichrome stain

Disadvantages of PVA

Dosent preserve helminth eggs/larvae and coccidia/microsporidia, Contains mercuric chloride which can be harmful, can't be used for concentration or immunoassays, can't use acid fast or safranin stain

What procedure allows for a wider range of testing with formalin

Conversion to formalin ethyl acetate

wet mount prep steps

Place small amount of formalin specimen on both sides, add iodine to one side, add a coverslip to preserve, seal, scan using 10x

How can we increase the chances of detecting organisms in small numbers

Separating parasites from fecal debris and removing the fecal debris

What are the two techniques for removing fecal debris?

Floatation and Sedimentation

Describe using floatation for fecal sample isolation

Uses solution with higher specific gravity, parasites float to top, debris sinks to bottom, often uses Zinc Sulfate or Sheathers Sugar

Advantages and disadvantages of Floatation

Pro: Cleaner than sedimentation

Cons: Walls of eggs and cysts can collapse, operculated (open) eggs do not float

Describe sedimentation use for fecal isolation

Uses solution with lower specific gravity to concentrate organisms in sediment at the bottom, most common solvent is formalin ethyl acetate

Advantages and disadvantages of Sedimentation

Pros: Easier to perform, contains operculated eggs

Cons: Fecal debris plug forms at top and needs to be popped out

What Is the most common use of PVA preserved samples?

Permanent staining with trichrome to ID protozoan cysts and trophs

What is the trichrome stain used for?

Confirmation of Protozoan ID

What are the colors produced by the trichrome stain

Green background, light blue/green to pink for protozoan cytoplasm, ruby red for protozoan karyosomes

What is the alternative for trichrome staining? Why is it used less?

Iron hematoxylin stain, produces less contrast

What colors appear from the iron hematoxylin stain?

Trophs and cysts appear blue gray, nuclei and inclusions darker than cytoplasm, all ends up being some shade of blue/gray

What is cellophane tape used for?

Collection of Enterobius Vermicularis eggs

What is the enterotest used for?

Collection of duodenal contents for parasitology exam

What is Knott concentration used for?

Concentration of samples suspected to have low organism numbers by slow speed centrifugation

What are Buffy coat slides used for?

Leishmania or Trypanosoma detection

What is Direct Fluorescent Antibody testing used for?

DFA is used for trichomonas vaginalis detection

What is Direct agglutination testing used for?

DAT used for leishmaniasis and Chagas diagnosis

What is an ELISA used for?

ID of Toxoplasma gondii

What is complement fixation used for?

Leishmaniasis, Chagas, and pneumocystis diagnoses

What is gel diffusion precipitation used for?

Detection of Amoebic infection

What is an Indirect immunofluorescent antibody (IFA) test used for?

Diagnose amoeba, malarial, schistosome and toxoplasmosis infection

When is the modified acid fast stain used? What does it do?

When suspecting Cryptosporidium parvum, Cyclospora cayetansis, and Cystoisospora belli; stains TB

What sample is used for the modified acid fast stain?

Fresh or Formalin fixed samples

What are we looking for in the modified acid fast stain?

Magenta pink organisms like trichrome stain, teal background