detection for clinical diagnosis is performed using the indirect fluorescent
antibody (IFA) test. The IFA procedure can be used as a
diagnostic tool to determine if a patient has been infected with
Plasmodium. Because of the time required for development of
antibody and also the persistence of antibodies, serologic testing is not
practical for routine diagnosis of acute malaria. However, antibody
detection may be useful for:
blood donors involved in cases of transfusion-induced malaria when the
donor's parasitemia may be below the detectable level of blood film
- testing a
patient with a febrile illness who is suspected of having malaria and from
whom repeated blood smears are negative
- testing a
patient who has been recently treated for malaria but in whom the
diagnosis is questioned
Species-specific testing is
available for the four human species: P. falciparum, P. vivax, P.
malariae, and P. ovale. Cross reactions often occur between Plasmodium
species and Babesia species. Blood stage Plasmodium species
schizonts (meronts) are used as antigen. The patient's serum is exposed to the
organisms; homologous antibody, if present, attaches to the antigen, forming an
antigen-antibody (Ag-Ab) complex. Fluorescein-labeled antihuman antibody is then
added, which attaches to the patient's malaria-specific antibodies. When examined with
a fluorescence microscope, a positive reaction is when the parasites
fluoresce an apple green color.
Enzyme immunoassays have also been
employed as a tool to screen blood donors, but are not recommended for
clinical diagnosis due to limited sensitivity.
Positive IFA result with P. malariae schizont antigen.
Sulzer AJ, and Wilson M. The
fluorescent antibody test for malaria. Crit Rev Clin Lab Sci 1971;2:601-609.