A new analysis of the prehistoric origin of malaria suggests that it evolved in insects at least 100 million years ago, and that the first vertebrate hosts of the disease were probably reptiles, which at that time would have included dinosaurs, according to a report from Oregon State University (OSU).
Malaria, which still kills more than 400,000 people a year worldwide, is thought to be of more-modern origin (ranging from 15,000 to 8 million years old), to be caused primarily by one genus of protozoa (Plasmodium), and to be spread by anopheline mosquitoes. But the ancestral forms of this disease used different insect vectors and different malarial strains, and may literally have helped shape animal survival and evolution on Earth, according to Dr. George Poinar, Jr., a researcher at OSU’s College of Science.
Poinar suggested in the journal American Entomologist that the origins of malaria, which today can infect animals ranging from humans and other mammals to birds and reptiles, may have begun in an insect, such as the biting midge, more than 100 million years ago. In previous work, Poinar and his wife implicated malaria and the evolution of blood-sucking insects as disease vectors that could have played a significant role in the extinction of the dinosaurs.
Understanding the ancient history of malaria evolution, Poinar said, might offer clues to how its modern-day life cycle works, how it evolved, and what might make possible targets to interrupt its transmission through its most common vector, the Anopheles mosquito.
Poinar was the first to discover a type of malaria in a 15- to 20-million-year-old fossil from the Dominican Republic. It was the first fossil record of Plasmodium malaria, one type of which is now the strain that infects and kills humans.
Even further back, malaria may have been one of the diseases that arose along with the evolution of insects and had a huge impact on animal evolution. In a 2007 book, Poinar and his wife argued that insects carried diseases that contributed to the widespread extinction of the dinosaurs around the “K-T boundary” approximately 65 million years ago.
“There were catastrophic events known to have happened around that time, such as asteroid impacts and lava flows,” Poinar said. “But it’s still clear that dinosaurs declined and slowly became extinct over thousands of years, which suggests other issues must also have been at work. Insects, microbial pathogens, and vertebrate diseases were just emerging around that same time, including malaria.”
In recent decades, avian malaria has been implicated in the extinction of many bird species in Hawaii, especially in species with no natural resistance to the disease. Different forms of malaria, which is now known to be an ancient disease, may have been at work many millions of years ago and probably had other implications affecting the outcome of vertebrate survival, Poinar said.
The first human recording of malaria was in China in 2,700 B.C., and some researchers say it may have helped lead to the fall of the Roman Empire. In 2015 there were 214 million cases worldwide, according to the World Health Organization. Immunity does not occur naturally, and a vaccine has yet to be developed.
Source: Oregon State University; March 25, 2016.