Hematologic characteristics of avian malaria cases in African black-footed penguins (Spheniscus demersus) during the first outdoor exposure season.

Twenty-nine juvenile, captive-reared African black-footed penguins (Spheniscus demersus) were hematologically monitored every 2 wk over the period of 24 wk during their first outdoor exposure. Blood samples taken from the penguins were screened for 12 blood evaluation parameters. Parasitemic penguins were medically treated. Eighteen birds (62.1%) experienced naturally acquired malaria and 11 birds (37.9%) remained nonparasitemic. A total of 32 avian malaria episodes were noted; 25 (78.1%) were identified as Plasmodium elongatum, 5 (15.6%) as Plasmodium relictum, and 2 (6.3%) as Plasmodium spp. One P. elongatum (3.4%) and 3 P. relictum (10.3%) infections were fatal. All deaths occurred during the first episode of parasitemia. Gross lesions of the birds that died included hepatomegaly and splenomegaly. Interstitial pneumonia with schizonts was observed on histological examinations. The range, mean, and SD of 12 hematological parameters were determined for nonparasitemic and parasitemic penguins. Differences between these groups in total white blood cell (WBC) counts and relative lymphocytosis (LYMPHS) were not significant. The combined classes of total WBC counts (> 20.0 x 10(3)/microliters) and LYMPHS (> 60.0%) are not indicative of avian malaria infection in African penguins. No correlations were found between changes in the values of blood parameters with season or age of penguins. Treatment of parasitemic birds significantly reduced expected mortality from 50.0% to 13.8%.