关于Nurseth的意思和用法的提问

A: "nurseth"
- it's the singular version of 'nurse' but in third person.

by "nurseth the disease" it means to "feed the disease" so, keep it alive and make it grow/become worse.

"doth"
- it's the singular version of 'do' but in third person.

by "Feeding on that which doth preserve the illness" it means to make the illness last longer.

Shakespeare, right?

For that which worsens the disease,
Feeding on that which makes it last longer,

Hope this helps. : )