Malaria from the age of the dinosaurs?

A researcher from Oregon State University, George Poinar, Jr, has claimed that malaria evolved in insects at least 100 million years ago. His research suggests that the first vertebrate hosts of this disease were probably reptiles, which at that time would have included the dinosaurs.

Malaria is often thought to be somewhere between 15,000 and 8 million years old, caused primarily by one genus of protozoa, Plasmodium, and spread by anopheline mosquitoes. But Poinar claims that the ancestral forms of this disease used different insect vectors and different malarial strains, and may have helped shape animal survival and evolution on Earth.

Poinar was the first to discover a type of malaria in a fossil dated to be 15 to 20 million years old, in what is now 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. Writing in the journal American Entomologist, Poinar suggests that earlier forms of the disease, carried by biting midges, are at least 100 million years old.

Since the sexual reproduction stage of malaria only occurs in insects, Poinar said they must be considered the primary hosts of the disease — not the vertebrate animals that they infect with disease-causing protozoa. He believes the evidence points toward the Gregarinida as a protozoan parasite group that could have been the progenitors of malaria, since they readily infect the insects that vector malaria today.

Furthermore, he suggested malaria may have been one of the diseases that arose along with the evolution of insects and had an impact on animal evolution. In the 2007 book What Bugged the Dinosaurs? Insects, Disease and Death in the Cretaceous, Poinar and his wife Roberta argued that insects carried diseases that contributed to the widespread extinction of the dinosaurs around the ‘K-T boundary’ about 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.”

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.

Image caption: This 100-million-year-old biting midge, preserved in amber, shows numerous oocysts of the malarial parasite Paleohaemoproteusburmacis, evidence of the oldest ancestral strain of malaria ever discovered. (Photo by George Poinar, Jr, courtesy of Oregon State University under CC BY-SA 2.0)