Nuclear explosions in the middle of the ocean are harmless. At least that's what everyone believed, so atomic bombs were tested in these areas. Only when it was too late did they discover that they had done something that would change humanity forever. Radiation from the explosions eventually caused a mutation in bacteria that lived in the region's air, becoming a new virus. Because they are so easily carried by the wind, the new virus has spread throughout the world.
What helped delay the discovery of the virus is that it has an incubation period, causing the infected person to begin to show signs later. It can be days, months, years, or even never manifest. But when the virus manifests itself, the infected person becomes an animal. Transformation is slow, with the infected becoming fully animal in about a year. During transformation, gender change can occur, making the person an animal of the opposite sex.
The most important fact, what a transformed human difference from normal animals is that although the body becomes fully animal, minds do not. The mind of an animal does not erase existing humanity, but merges with it. Therefore, transformed people retain all knowledge of when humans, including the ability to speak, but acquire customs of the animal they have become. They also the life span of a human being.
We will accompany someone through the transformation, and that person will be is ....