According to a report in New Scientist, Iris Levin of the University of Missouri at St Louis and her colleagues took blood samples from 362 Galapagos penguins - already listed as being threatened with extinction - on nine islands in the Galapagos archipelago.
All of the birds appeared healthy, but the tests revealed that 19 of the penguins, 5 per cent, carried the Plasmodium parasite, which causes malaria.
The infected birds were spread across the archipelago, suggesting the parasite is not restricted to one small colony of penguins.
Galapagos penguins move around the islands, so the parasite is likely to spread further, according to the researchers.
"Plasmodium in Galapagos penguins is potentially disastrous for this species," said Bruce Hofkin, a parasitologist at the University of New Mexico in Albuquerque.
"Most penguin species are very susceptible to Plasmodium and avian malaria is a real problem in zoos, where it is a major problems in penguin exhibits," he added.
The mosquitoes that can carry Plasmodium arrived on the archipelago in the 1980s, presumably on incoming boats or flights.
Researchers have been concerned that the parasite may take hold but had not found any evidence of it until now.
Levin said that although the birds were healthy, there is still cause for concern.
The biologists point out that Plasmodium has decimated wild bird populations in Hawaii; that the strain they found is closely related to a strain that causes avian malaria in captive penguins; and that the Galapagos penguins are unlikely to have encountered the malaria parasite before, making them vulnerable to it.
One other factor concerns them at least as much as all of the above is the El Nino phenomenon. The reduction in fish numbers during El Nino seasons can slash the penguin population in the Galapagos by up to 80 per cent.
The researchers fear that this could trigger malaria symptoms and deaths in infected birds.
Although the Galapagos penguin population has been on the rise since the major El Nino event of 1997-98, when the penguins are thought to have been free of Plasmodium, it is still only half of what it was before.
Other research has suggested that stress can increase the death rate among birds that have malaria, and computer models suggest El Nino events may become slightly stronger with climate change. (ANI)