Parasites in general Flashcards
parasite
an organism that lives in or on and takes its nourishment from another organism ( the host)
cannot live independently
parasitism
the relationship between species ( host & organism) wherein one of the species ( parasite ) benefits at the expense of the other (host)
parasitic disease
includes infections by protozoa, helminths & arthropods
protozoa
Single-celled eukaryotes, either free-living or parasitic,
which feed on organic matter such as other microorganisms or organic tissues and debris
Helminths
Worm-like parasites that survive by feeding on a living
host to gain nourishment and protection, sometimes resulting in illness of the host
Arthropods
Invertebrate animal that has an exoskeleton, a
segmented body and jointed appendages
- Can be parasites themselves or act as a host or vector for other
microorganisms
Endoparasites vs Ectoparasites
> Endoparasites - Live inside the host organism
Ex. Protozoa and Helminths
> Ectoparasites - Live on the surface of the host organism
Ex. Arthropods
Parasitology
Parasites are important causes of human morbidity and
mortality
Not a common cause of disease in developed countries
In recent years, health care professionals have become
increasingly aware of parasites as possible causes of
disease/infection
> Increased number of immunocompromised patients
> Increased travel to high risk areas (endemics)
> Growing population of immigrants
Transmission
> Venereal transmission (sexual contact)
- Trichomonas vaginalis
> Ingestion of contaminated food or water
- Giardia lamblia
- Cryptosporidium spp.
> Skin penetration of infective larvae
- Strongyloides stercoralis
- Hookworm
> Bites of various arthropods
- Plasmodium
- Trypanosoma
- Leishmania
pathogenesis
The pathogenic mechanism of a parasitic infection varies
according to species and quantity of parasites as well as
parasite-host adaptation and host responses
The damage caused by parasites can be either confined
within the parasitic site or extend into other parts of the
host
Disease can range from mild to serious and life-
threatening
The life cycles of parasites are important in the
pathogenicity
SPECIMEN COLLECTION
The specimen collected will depend on the potential
parasite, the patient’s symptoms and clinical
history/travel history
Examples of specimens submitted for parasitic identification include: > Fecal Specimens > Urine, Vaginal and Urethral Specimens > Sputum > Blood Smears > Biopsy Specimens > Cerebrospinal Fluid > Other Intestinal Collection Techniques
Multiple specimens may need to be collected
- Depending on specimen type and parasites
lifecycle
Ex. Multiple fecal specimens collected over a 10-day
period
Appropriate collection containers/techniques used
Proper preservatives used and in the correct ratio
Commercial systems available (Container +
Preservative)
Specimens should be collected prior to administration
of antimicrobials
(and prior to a barium enema in the case of stool
collection)
specimen transport
Samples should be transported immediately to the
laboratory or preservatives should be used if a lag time
exists
Preservatives maintain parasite morphologic
characteristics
Processing depends on the use of
•Appropriate fixatives
•Immediate fixation upon arrival
•Adequate mixing of fixative and specimen
PROCESSING
Preservation of Specimens
> Depend on transport time to laboratory, procedure
performed and the testing to be performed
> Examples include:
- Polyvinyl Alcohol (PVA)
- 10% Formalin (NBF)
- Sodium Acetate Acetic Acid Formalin (SAF)
- Merthiolate Iodine Formalin (MIF)
- Single Vial Systems
A two-vial system is commonly used for
fecal samples
•5% or 10% formalin for immunoassays
•Polyvinyl Alcohol (PVA) for stained smears
15
PVA
PVA (STOOL ADHESIVE)
> PVA stands for polyvinyl alcohol, a plastic powder/resin that
is incorporated into the liquid fixative
Serves as an adhesive to “glue” the stool material onto the
slide
PVA itself has no preservation capability and is inert
in terms of fixation
UNIVERSAL FIXATIVES
PVA and Formalin are hazardous and pose exposure and disposal concerns
Alternative preservatives have been adapted
Examples of “Universal Fixatives” are
SAF (no mercury or PVA, contains formalin)
TOTAL-FIX (no mercury, PVA or formalin)
ECOFIX (no mercury or formalin, contains PVA)
Currently, TOTAL-FIX is the only fixative that does not contain formalin,
PVA or mercury
