Characteristics of naturally acquired avian malaria infections in naive juvenile African black-footed penguins (Spheniscus demersus)

Antibody responses to naturally acquired Plasmodium relictum and P. elongatum infections, blood parasitemia, and disease signs were investigated in 23 naive juvenile African black-footed penguins (Spheniscus demersus). Anti-Plasmodium spp. immunoglobulins were detected by enzyme-linked immunosorbent assay (ELISA) using P. falciparum antigens. All birds rapidly developed antibody to P. relictum and P. elongatum. Five penguins showed detectable parasitemia and signs of the disease. Parasitemia was not related to the timing of the maximal antibody response or to the antibody titer. Two of the five parasitemic birds died and gross examination revealed splenomegaly, hepatomegaly, and congested, edematous lungs. Although the other 17 birds were clearly exposed to the disease, none showed signs of infection. No subsequent episode of parasitemia was observed in individual penguins. A comparison of the fate of 1993 penguins with those from other years showed a great variability in the proportion of birds exhibiting signs of malaria.