The most common and most likely answer to this crossword clue is the 6 plus 7 letter word GERMAN MEASLES
I've seen this crossword clue in The Daily Telegraph
G
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M
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M
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More clues leading to the result GERMAN MEASLES
- In the wake of micro-organism there’s a nameless horrible disease
- Illness caused by bug — one given various names by the French
- Bug set off a nameless illness
- A nameless germ spreading disease
- Virus leads to a development of lameness producing complaint
- Disease from microbe, a nameless disorder
- Bug with exotic name like ‘the Continental Disease’
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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.