The most common and most likely answer to this crossword clue is the 10 letter word INFECTIOUS
I've seen this crossword clue in The Daily Telegraph
I
N
F
E
C
T
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S
More clues leading to the result INFECTIOUS
Buddy explains!

The straight part
We know that "Catching" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case catching = infectious.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 INFECTIOUS mean?
INFECTIOUS adjective- (of an illness) Transmitted from one person to another, usually through the air breathed.
- (of a person) Able to infect others.
- (of feelings and behaviour) Spreading quickly from one person to another.
- Memorable and invoking excitement or interest.