Host population persistence in the face of introduced vector-borne diseases: Hawaii amakihi and avian malaria

TLDR

The last 25 years have seen an unprecedented rise in emerging infectious diseases, threatening human and wildlife populations. The study investigated how Hawaiian forest birds, especially the native amakihi, persist amid introduced avian malaria and vectors, aiming to uncover mechanisms that could guide disease mitigation. Researchers surveyed birds, parasites, and vectors across nine sites from sea level to 1,800 m on Mauna Loa during 2002. Contrary to expectations, amakihi remained abundant at low elevations despite 24–83 % malaria infection rates and year‑round transmission, suggesting ecological or evolutionary adaptations that enable recolonization.

Abstract

The past quarter century has seen an unprecedented increase in the number of new and emerging infectious diseases throughout the world, with serious implications for human and wildlife populations. We examined host persistence in the face of introduced vector-borne diseases in Hawaii, where introduced avian malaria and introduced vectors have had a negative impact on most populations of Hawaiian forest birds for nearly a century. We studied birds, parasites, and vectors in nine study areas from 0 to 1,800 m on Mauna Loa Volcano, Hawaii from January to October, 2002. Contrary to predictions of prior work, we found that Hawaii amakihi (Hemignathus virens), a native species susceptible to malaria, comprised from 24.5% to 51.9% of the avian community at three low-elevation forests (55-270 m). Amakihi were more abundant at low elevations than at disease-free high elevations, and were resident and breeding there. Infection rates were 24-40% by microscopy and 55-83% by serology, with most infected individuals experiencing low-intensity, chronic infections. Mosquito trapping and diagnostics provided strong evidence for year-round local transmission. Moreover, we present evidence that Hawaii amakihi have increased in low elevation habitats on southeastern Hawaii Island over the past decade. The recent emergent phenomenon of recovering amakihi populations at low elevations, despite extremely high prevalence of avian malaria, suggests that ecological or evolutionary processes acting on hosts or parasites have allowed this species to recolonize low-elevation habitats. A better understanding of the mechanisms allowing coexistence of hosts and parasites may ultimately lead to tools for mitigating disease impacts on wildlife and human populations.