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The island of Hawai‘i in the US may be facing a silent epidemic. Nearly every forest bird species in the region is capable of transmitting a deadly disease that has already led to extinctions. In a February study published in the journal Nature Communications, a team of US scientists analysed blood samples from more than 4,000 birds in Kaua‘i, O‘ahu, Maui and Hawai‘i islands. In 63 of the 64 sites, they detected presence of avian malaria in birds. Avian malaria is a vector-borne disease, in which parasites enter birds’ bloodstream through mosquito bites and damage red blood cells, causing anaemia and organ failure.
The study found that in some cases, birds had chronic avian malaria for months or years, transmitting the parasite Plasmodium relictum, via mosquitoes. These findings may help explain why avian malaria is widespread in Hawai‘i, with previous studies detecting the presence of the parasite among all mosquitoes on the islands. The infection was detected here as early as 1826, after a southern house mosquito (Culex quiquefasciatus) was introduced accidentally to the islands and transmitted P relictum, for which the birds had no immunity. Since then, the disease has driven population declines and extinctions in native Hawaiian honeycreepers. The infection reduced the number of honeycreeper species from 55 to just 17. Most honeycreepers are now restricted to elevations too cold for mosquitoes.
Avian malaria has been detected globally, from parrots in Europe to wild birds in Guatemala. It is also common among captive populations, for example, in 2022, Humboldt penguins in zoos across Thailand died due to the disease.
The threat is unfolding in India, specifically in the Shola Sky islands, tropical evergreen forests 1,200-2,600 metres above sea level in the Western Ghats. Scientists have been monitoring susceptibility of birds on the islands to diseases like avian malaria for over a decade. The Shola Sky islands differ from Hawai‘i, in that three genera—Plasmodium, Haemoproteus and Leucocytozoon, together called avian Haemosporidian parasites—have been found here. Haemoproteus and Leucocytozoon species are not spread by mosquitos but by other vectors like biting midges and black flies, respectively. They are also specialist parasites …
This article was originally published in the July 1-15, 2026 print edition of Down To Earth, which also features exclusive graphics on avian malaria parasites in India
