New Study Uncovers Widespread Transmission of Avian Malaria Among Hawaiian Birds

A recent study from the University of Hawaiʻi at Mānoa has revealed a concerning trend: nearly every forest bird species in Hawaiʻi is capable of transmitting avian malaria. This widespread transmission helps explain the prevalence of the disease, particularly in areas where mosquitoes thrive.

Published in Nature Communications on February 10, the research detected avian malaria in 63 out of 64 monitored locations statewide. These study sites spanned forests with varied bird species, and the disease stems from the parasite Plasmodium relictum. This pathogen has significantly impacted native Hawaiian honeycreepers, contributing to their alarming decline and even extinction.

According to Christa M. Seidl, who led the study as part of her PhD at the University of California, Santa Cruz, "Avian malaria has taken a devastating toll on Hawaiʻi's native forest birds, and this study shows why the disease has been so difficult to contain." Seidl emphasized that with so many birds capable of hosting the parasite, effective strategies for protecting these vulnerable species are limited and necessitate rigorous mosquito control efforts.

The implications are dire: avian malaria attacks red blood cells, leading to anemia and organ failure, significantly lowering survival rates. Research indicates that the ʻiʻiwi, a scarlet honeycreeper, suffers around a 90 percent mortality rate if infected. Tragically, the ʻakikiki, another localized honeycreeper, is now considered extinct in the wild due primarily to this disease.

This study challenges the common understanding of how avian diseases spread. Unlike many infectious diseases that depend on a few host species, avian malaria in Hawaiʻi can be sustained by a broad range of birds, both native and introduced. Each of these species can transmit the pathogen to the southern house mosquito, the primary vector for the disease, even if harboring low levels of the parasite. This dynamic allows various bird populations to facilitate ongoing transmission.

"We often understandably think first of the birds when we think of avian malaria," Seidl pointed out, "but the parasite needs mosquitoes to reproduce, and our work highlights just how efficiently it infects them through many different birds." This insight underscores the complexity of managing the disease and its vectors.

Researchers analyzed blood samples from over 4,000 birds across major Hawaiian islands, including Kauaʻi, Oʻahu, Maui, and Hawaiʻi Island. Their findings revealed that both native and non-native bird species displayed similar levels of infectivity, meaning the entire avian community contributes to the ongoing transmission of avian malaria.

Another critical takeaway is that infected birds can sustain chronic infections for extended periods, some lasting months or even years. During these phases, birds may show minimal signs of illness yet remain capable of infecting mosquitoes. The researchers estimate that this prolonged, low-to-moderate infectious stage likely drives the majority of viral transmission across the islands.

This versatility of the parasite in using a wide array of avian hosts likely explains its rampant presence throughout Hawaiʻi. The study suggests that few areas infested with mosquitoes remain unaffected by the risk of avian malaria transmission. Compounding the issue, rising temperatures are facilitating the spread of mosquitoes and the accompanying disease into higher elevation zones, which previously served as safe havens for sensitive native bird populations.

Seidl and her collaborators at the Maui Forest Bird Recovery Project are part of the initiative known as Birds, Not Mosquitoes. This effort brings together academic, state, federal, non-profit, and industry partners focused on enhancing mosquito control strategies to support the conservation of Hawaiian birds.

The Maui Forest Bird Recovery Project operates under the Pacific Cooperative Studies Unit in the College of Natural Sciences. All birds involved in the study were captured and handled by qualified ornithologists under appropriate state and federal permits.

Material provided by the University of Hawaii at Manoa. Note: Content may be edited for style and length.