The Hawaiian archipelago (upper right) is one of the most isolated island chains in the world. The few species of land birds that were able to cross 2,000 miles of open ocean to colonize these islands found a true paradise with no biting flies or vector-borne parasitic diseases. This natural quarantine was broken by the accidental introduction of mosquitoes (middle) in the 1820's and mosquito-transmitted avian diseases such as pox and malaria. Ornithologists working in the islands in the late 1800's described sick and dead forest birds with debilitating pox lesions (lower right) and it is now thought that a combination of one or both of these diseases caused devastating epidemics in non-immune populations of endemic forest birds. Scientists collected evidence for this in the late 1950's by exposing caged forest birds on the island of Kauai in lowland habitats where mosquito populations were high. Birds exposed in these areas rapidly developed fatal infections of pox and malaria. When native and non-native birds were infected in the laboratory by inoculation of infected blood, native birds developed higher parasitemias and had higher mortality than non-native species. These early studies have been criticized, however, for their small sample sizes and/or failure to duplicate natural conditions of transmission.
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| This project is designed to provide definitive evidence through carefully controlled laboratory experiments to either support or refute these previous studies. We have been able to reproduce the lesions, morbidity and mortality observed in naturally-infected wild birds in the laboratory. These studies have provided evidence that some native species, like the Iiwi (Vestiaria coccinea, right) are so susceptible to malaria that a single infective mosquito bite can lead to a fatality rate of 90%.
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This work has been essential for providing researchers and resource managers concrete and convincing evidence that current elevational and geographic anomalies in the distribution of some native species are likely due to the presence of this disease.
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| Experimental infections have also been used to identify individuals with some innate immunological resistance to malaria. Blood and tissues from these birds are being analyzed by researchers at PIERC and the Smithsonian Institution to find genetic markers for disease resistance. |
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