Wildlife disease and conservation in Hawaii: pathogenicity of avian malaria (Plasmodium relictum) in experimentally infected Iiwi (Vestiaria coccinea).
The susceptibility of Hawaiian native Vestiaria coccinea (Iiwi) and non-native Lonchura punctulata (Nutmeg Mannikins) to an isolate of Plasmodium relictum was determined. Food consumption, weight, and parasitaemia were monitored in juvenile Iiwi that were infected by either single (low-dose) or multiple (high-dose) mosquito bites. Mortality in both groups was significantly higher than in uninfected controls, reaching 100% of high-dose birds and 90% of low-dose birds. Significant declines in food consumption and a corresponding loss of body weight occurred in malaria-infected birds. Both sex and body weight had significant effects on survival time, with males more susceptible than females and birds with low initial weights more susceptible than those with higher initial weights. Gross and microscopic lesions in malaria fatalities included massive enlargement of the spleen and liver, hyperplasia of the reticuloendothelial system with extensive deposition of malarial pigment, and overwhelming anaemia in which over 30% of the circulating erythrocytes were parasitized. Nutmeg Mannikins, by contrast, were completely refractory to infection. These findings support previous studies documenting high susceptibility of native Hawaiian forest birds to avian malaria.