ZOOL 452January 9, 2014
Diagnosis of Parasitic Infections
• Microscopy = still the method that is mainly used to diagnose infection. Most
inexpensive; used a lot in the developing world. This is direct diagnosis. You
actually see the parasite and identify it.
• Stool needs to be concentrated so that it can be examined under the microscope
o Sugar solutions are used to do this (floatation method). They allow
parasites to float in the surface.
o Output of stool per day for humans = 400g. It would take forever to look
at that. That is why you need to concentrate t his
• Direct biopsies of the affected area can be used for direct diagnosis. Eg you can
do this with Leishmania and the filarial worms. You can take a snippet of the skin
for things like Onchocerca to find the microfilaria.
• Concentration and tissue sampling ▯main methods of parasite diagnosis
• Serology ▯used to see if a person has been previously exposed to parasites. Eg: If
you have been infected with Giardia, you will find antibodies against Giardia in
the person’s blood. This sort of thing would be done using ELISA (enzymelinked
immunosorbent assay) or antigen capture, which is a variation of ELISA.
o Antigen capture ELISA measures the presence of the parasite antigen. It
can be used to tell you if the parasite is currently present.
• Regular ELISA Procedure Information
o Done with 96well plate. Coat well with the parasite antigen. Then, to the
well, add a serum sample to see if the person has antibodies to the parasite.
If there are antibodies to the antigen in the serum, they will bind to the
antigen. Then, you wash the serum sample off. After this, add an antibody
that recognizes the constant portion the antibody that was meant to
recognize the parasite antigen (antiantibodies). The antiantibodies are
tagged with an enzyme (eg: alkaline phosphatase).
o Add something to the well that would react with the enzyme, so that you
would see which antiantibodies have found the antibodies in the serum.
o You can read the optical density of the colour that would be produced
because of the enzymatic activity.
• Antigen Capture ELISA Procedure Information (aka sandwich ELISA)
o Coat the well with antibodies that recognize a specific antigen of the
o Add the serum (test sample) to the well. If there are antigens in the test
sample, they will be recognized by the antibodies that were originally
o Then, add an antibody of a different species that will recognize it.
o The rest of the steps are the same as with the regular ELISA test
o Equipment needed for ELISA
Micropipette (each on = $400)
Microtitre plate (each on is $5) Spectrometer to measure the optical density = super expensive
Antibodies = SUPER expensive
This whole deal is WAY too expensive for it to be used regularly in
the third world
• Immunofluorescence Procedure (eg: if you have a Trypanosoma sp. and you want
to know if someone has been infected with that before
o Antibodies that bind to Trypanosoma antigens attach themselves to those
antigens on the surface of the parasite. Those antigens are tagged with
fluorochromes (eg: FITc)