Antibody Detection
Malaria antibody 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:

• screening blood donors involved in cases of transfusion-induced malaria when the donor's parasitemia may be below the detectable level of blood film examination
• 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.

A

A: Positive IFA result with P. malariae schizont antigen.

Reference:

Sulzer AJ, and Wilson M. The fluorescent antibody test for malaria. Crit Rev Clin Lab Sci 1971;2:601-609.