The most common and most likely answer to this crossword clue is the 8 letter word SMALLPOX
S
M
A
L
L
P
O
X
More clues leading to the result SMALLPOX
Buddy explains!

The straight part
We know that "Ailment" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case ailment = smallpox.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 SMALLPOX mean?
SMALLPOX noun- An acute, highly infectious often fatal disease caused by Variola virus of the family Poxviridae. It was completely eradicated in the 1970s. Those who survived were left with pockmarks.