The title is confusing but I can explain. This question originates from this post on why Zika is capitalised while chikungunya and yellow fever were not. The consensus was that Zika originated from Zika the African forest (and hence a proper noun) while the other two were just descriptions and hence not proper nouns, are not capitalised ("chikungunya" from a common Makonde word meaning "something bending up" and yellow is pretty self-explanatory)
But there's an outlier in this convention. ampere is the SI unit for current named after Ampere the scientist and I remember reading that we should not confuse Ampere with ampere as the first refers to the scientist and the latter to the unit of current. So why is there this exception?