No, disease names are not proper nouns, although diseases named after people keep the capitalization of the person’s name (Münchausen syndrome).
The scientific (Latin) names of disease-causing organisms follow the standard rule of Genus species.
Which diseases are capitalized?
Diseases named after people are capitalized.
Some disease names are capitalized because they are named after the person who discovered them. For example, Alzheimer’s disease is named after a German doctor named Alois Alzheimer, and Down’s syndrome is named after a British doctor named John Langdon Down.
Should the names of disorders be capitalized?
The blog referred me to Merriam-Webster’s Collegiate Dictionary (2005) and the APA Dictionary of Psychology; I checked both. There is no indication of disorders or syndromes being capitalized unless they are named after a person, such as Asperger syndrome. Even then “syndrome” is not capitalized.
Do you capitalize common names?
Rules for writing common names: modern English doesn’t capitalize common names of plants (or animals, tho bird specialists sometimes do capitalize bird common names). The plant common name has to conform to the rules of English, however, so if there’s a proper noun in the common name, it must be capitalized.