The most common and most likely answer to this crossword clue is the 6 letter word RABIES
I've seen this crossword clue in The Times
R
A
B
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The straight part
We know that "Dangerous disease among animals" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case dangerous disease among animals = rabies.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 RABIES mean?
RABIES noun- An infectious disease caused by species of Lyssavirus that causes acute encephalitis in warm-blooded animals and people, characterised by abnormal behaviour such as biting, excitement, aggressiveness, and dementia, followed by paralysis and death.