Intake issue to afflict gunwales with HMAS Supply? (6)

I believe the answer is:

asthma

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'intake' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for asthma that I've seen before include "Common breathing ailment" , "Breathing illness" , "Distressing ailment affecting breathing" , "Bronchial allergy" , "Physical disorder" .)

I've seen this clue in the Sydney Morning Herald.

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