Indirect Fluorescent Antibody Test

Malaria antibody detection is performed using the indirect fluorescent antibody (IFA) test. The IFA procedure can be used 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, usually from an endemic area, who has had repeated or chronic malaria infections for a condition known as tropical splenomegaly syndrome
• Testing a patient who has been recently treated for malaria but in whom the diagnosis is questioned.

Species-specific testing is available for three of the four human species: P. falciparum, P. vivax, and P. malariae. P. ovale antigens are not always readily available and so antibody testing is not performed routinely. 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 anti-human antibody is then added, which attaches to the patient's malaria-specific antibodies. When the slide is examined with a fluorescence microscope, if parasites fluoresce an apple green color, a positive reaction has occurred.

Enzyme immunoassays have also been employed as a tool to screen blood donors, but have limited sensitivity due to use of only Plasmodium falciparum antigen instead of antigens of all four human species.

Indirect fluorescent antibody (IFA) test. The fluorescence indicates that the patient serum being tested contains antibodies that are reacting with the antigen preparation (here, Plasmodium falciparum parasites).