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Insidious

An insidious disease is any disease that comes on slowly and does not have obvious symptoms at first. The person is not aware of it developing.

References

Stedman's Online Medical Dictionary. Available at: www.stedmansonline.com/content.aspx?id=mlrI1400010956&termtype=t. Accessed April 21, 2015.

Update Date 4/11/2015