The most common and most likely answer to this crossword clue is the 7 letter word MALARIA
I've seen this crossword clue in The Daily Telegraph
M
A
L
A
R
I
A
More clues leading to the result MALARIA
- Girl swallowing aluminium for a fever
- Girl touring US city gets disease
- Bad French song – it’s infectious!
- Woman catching the French disease
- A shocker ultimately within African country, a disease
- Killer song, a hit written up
- Girl catching the French disease
- Disease of higher degree student on song
- Set alarm on one with a disease that’s infectious
- Disease brings false alarm to borders of India
Buddy explains!

The straight part
We know that "disease" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case disease = malaria.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does MALARIA mean?
MALARIA noun- A disease spread by mosquito, in which a protozoan, Plasmodium, multiplies in blood every few days.
- Supposed poisonous air arising from marshy districts, once thought to cause fever.