Development of a Serological Test
for Avian Malaria

Previous studies of avian malaria in Hawaii have been based on microscopic examination of Giemsa-stained blood smears (right) to diagnose infected forest birds. While this technique is still considered the "gold standard" for diagnosing malaria, it lacks the sensitivity to detect low-level chronic infections.

Chronically-infected birds have recovered from the most serious pathogenic effects of acute infections and developed strong humoral (antibody) and cellular immunity to the parasite. Recovered individuals, like this

Elepaio (Chasiempis sandwichensis ridgwayi) probably remain infected with malaria for life, but appear healthy and are able to control the infection. They may experience relapses at times of stress, however, and it is not clear what long-term effects these chronic infections have on reproductive success and overall fitness.

Accurate identification of chronically-infected birds is particularly important because they have survived acute infection and may carry genes responsible for disease resistance. This makes them good candidates for efforts to restore forest bird populations at low elevations where large areas of suitable habitat (right) still remain.

Accurate identification of chronically-infected individuals is also important in epidemiological studies, because these birds provide a living record of prior episodes of malaria transmission. As a result, serological analysis of blood samples collected from wild birds (right) can document presence of the disease when mosquito numbers are low and parasites can not be easily found by examination of blood smears.

Persistence of chronic malarial infection stimulates production of parasite specific antibodies that may be detected by an appropriate serological method. These antibodies are present in the bloodstream at times when parasites have disappeared from the circulation or dropped below numbers that can be detected by microscopy or polymerase chain reaction (PCR) methods. We have developed and evaluated a new serological assay for avian malaria that is based on standard immunoblotting techniques. This test is based on electrophoretic separation of a crude red blood cell extract of parasite antigens (lower left) and transfer of the antigens to a membrane that can be incubated with sera from individual birds (lower right).

This test uses microliter quantities of plasma, making it useful when quantities of available plasma are small. We are currently evaluating this diagnostic method against other published techniques to measure relative accuracy and specificity. Preliminary results indicate that it is more specific than existing enzyme-linked immunosorbant assay (ELISA) techniques and more sensitive than PCR methods for diagnosing chronic infections. We are using this technique in combination with blood smears to screen forest birds from both high and low elevation habitats for infection with avian malaria.

Avian Malaria in Hawaii

Development of a Serological Testfor Avian Malaria

Development of a Serological Test
for Avian Malaria