When was it discovered that bacteria and viruses can get sick?

A microbiologist working at the Pasteur Institute in Paris discovered what he described as an invisible, antagonistic microbe, that had a parasitic relationship with bacteria in 1917. He called it a bacteriophage (from phagein, "to eat"), a virus that infects bacteria.

In 2008, scientific researchers from the Universite de la Mediterranee in Marseille, France, identified an exceptionally large virus infecting an amoeba. They named it mamavirus, and soon they discovered another layer to the microscopic nesting dolls.

The amoeba's virus was itself infected by a much smaller virus. Sputnik, as the researchers called it, was the first member of a new class of viruses that scientists decided to call virophages, viruses that infect other viruses.

Sputnik has trouble multiplying without the preferred viral host; however, once an amoeba is infected with the mamavirus, Sputnik hijacks the mama's cellular machinery and multiplies at its expense. It produces more Sputniks while the mamavirus' own replicated particles assemble abnormally. The mechanics of it are fairly similar to what the mamavirus does to the amoeba. In effect, the virus is getting a taste of its own medicine.