Comparison of the diagnostic value of serum immunoglobulin levels, an enzyme-linked immunosorbent assay and a fluorescent antibody test in experimental infections withTrypanosoma evansiin rabbits

Abstract

Rabbits were infected with clones prepared from isolates of T. evansi from West Africa and South America. Estimations of parasitemia and hematological values were made during infection and after therapeutic treatment with suramin. Sera were obtained for estimations of immunoglobulin (Ig) levels by single radial diffusion techniques and antibody [Ab] levels by ELISA [enzyme-linked immunosorbent assay] and IFAT [indirect fluorescent Ab test] in order to compare the diagnostic efficiency of these tests. Serum IgM values increased between 5-20 times pre-infection levels within 15 days of infection and, except in 1 animal, returned to pre-infection levels within 43 days of treatment. IgG values increased 2-fold after infection and declined after treatment. Both ELISA and IFAT detected trypanosomal Ab in sera of rabbits 15 days after infection with T. evansi. Ab persisted in the treated animals and were still detectable at low levels several mo. after treatment. There was no difference between antigens prepared from different isolates of T. evansi for use in ELISA, but there were differences in the host response elicited by clones of different isolates. There was no difference in potential diagnostic efficiency between ELISA and IFAT, but ELISA has certain advantages in requiring less expensive equipment and allowing a quantitative assessment of results. The diagnostic value of raised serum Ig levels merits further investigation.