Please have a look at the definitions on Oxford Dictionary site: http://oald8.oxfordlearnersdictionaries ... es#disease
The example given on that site,
"A fatty diet increases the risk of heart disease." is very appropriate and similar to the correct use regarding your question. Although the second possibility, using the word as a countable noun, is also acceptable. Let's say that both are correct, depending on the intention of whom is writing or saying the sentence.
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