I think that dyslexia should be considered a disease over a mental disorder. I think that the fact that it is genetic and does not really cause a lot of mental issues makes it more of a disease than a mental disorder. Also I think it would be safe to say it has traits of both.
Dyslexia generates in the mind, and needs to be treated as such. Diseases can be treated, but mental disorders are managed. This is exactly what is done with dyslexia. Without the correct ongoing management and tools, dyslexia can be treated inappropriately. There isn't a magic pill that will make dyslexia go away.
I believe that it should be classified as a mental disorder, but this does not make it any less serious. Dyslexia is a serious issue that negatively affects many peoples lives, and should be treated immediately. The reason that I consider it a mental disorder though is because it does not directly effect ones health.
No, dyslexia should not be considered a disease, because it is not something that you contract. It is not like you will catch dyslexia if the person sitting next to you has it. Dyslexia shouldn't really be considered a disorder, either, but it is closer to a disorder than it is a disease.
I do not like the idea of Dyslexia being classified as a disease or a mental disorder; however, if I am forced to pick one I would go with mental disorder since Dyslexia has to do with how a persons mind is wired. Personally, I think Dyslexia is just a challenge for those who have it. They might have to work a little harder but calling it a mental disorder or a disease is a little harsh.