5 Diseases That Don’t Spread the Way We Used to Think

A malaria awareness activist in Lagos, Nigeria in April 2015 © PIUS UTOMI EKPEI/AFP/Getty Images

The ancient Egyptians described malaria in the Ebers Papyrus 4,000 years ago, although evidence in 30-million-year-old fossils suggests the disease has been with us for much longer. In 400 B.C.E., Greek physician Hippocrates described malaria's symptoms and characteristics in his treatise "On Airs, Waters, and Places." During the first half of the first century in the Roman Empire, Celsus left behind clinical descriptions of it. And during the third century, Quintus Serenus Sammonicus, physician to the Roman emperor Caracalla, prescribed wearing an amulet inscribed with the word "abracadabra" for nine days as treatment.

For thousands of years we've known malaria to be a contagious and fatal condition, but it took us a really long time to figure out how it spreads among people. Hippocrates, for example, blamed it on unhealthy air and poisonous gasses; the disease was nicknamed "marsh fever." It's also been associated with supernatural causes.

We didn't know the true cause of malaria until 1880, when French scientist Alphonse Laveran discovered that it's a parasitic infection. Specifically, it's the Plasmodium parasite that's responsible for the disease, and there are four species that infect humans: P. falciparum and P. vivax (the two most common) and P. malariae and P. ovale. It would be nearly 20 more years before scientists discovered this blood parasite is transmitted through the bite of infected female Anopheles mosquitoes. In 1902 Ronald Ross won the Nobel Prize for Physiology or Medicine for his discovery that the Plasmodium parasite lives and breeds in the gastrointestinal system of mosquitoes.