To declare something a disease (rather than simply a part of life) is to declare it unacceptable and in need of treatment by doctors.
A disease is something that needs to be treated.
A disease is not always something that needs to be treated.
The two people are in the boat.
There are a crowd of people at a Chinese funeral.
Two women are talking while they sit together.
the children are asleep
A cat is cleaning her babies
We're not doing anything?