"est causé par"?
"causée" would do, since "maladie" is feminine.
Can I translate that to:
"This illness is due to a virus"?
What is the infinitive form of "due" please?
Devoir.
The passive phrase "être dû à" is "to be due to".
The passive "être dû" is "to be owed".
Very funny Duolingo...