ELISA method for detecting anti-Plasmodium relictum and anti-Plasmodium elongatum antibody in infected duckling sera using Plasmodium falciparum antigens.

An enzyme-linked immunosorbent assay (ELISA) with 3 Plasmodium falciparum NF-54 antigens, R32tet32, P.F.R27, and crude red blood cell extract (CRBCE), was tested for detection of anti-Plasmodium relictum and anti-Plasmodium elongatum antibodies in sera from experimentally infected ducklings. Whole blood, serum, and dried blood on filter paper gave similar results. The latter was selected for convenience. All birds infected by experimental blood challenge, but not exposed to sporozoites, had detectable antibody (up to 1.0 x 10(-3.8) dilution) reactive with R32tet32, P.F.R27, and CRBCE antigens. Ducklings infected with P. elongatum had higher antibody levels than those infected with P. relictum. In a blind trial, the described ELISA accurately distinguished sera taken from infected and uninfected ducklings. This study provides the first evidence on cross reactivity in the ELISA format between P. falciparum antigens and antibodies induced by P. relictum and P. elongatum in experimentally infected ducklings. The proposed ELISA is fast, easy to perform, reproducible, and requires a minimal amount of equipment. The assay can be used for the detection of P. relictum and P. elongatum antibodies in captive or wild ducks, along with monitoring the level of antibody in selected groups of birds or for surveys of laboratory experiments where evidence of infection is required.