noun which may take the genitive case particle 'no', noun
Medical term used attributively to describe something caused by or related to a virus, such as infections or diseases.
ウイルス性の感染症が流行している。
A viral infectious disease is going around.
この症状はウイルス性のものだと考えられる。
These symptoms are thought to be viral in nature.
The noun 'virus'; ウイルス性 is the adjectival form meaning 'viral'.
Compound of ウイルス (virus) + 性 (nature, -ity), forming a no-adjective meaning 'viral'. The word ウイルス itself is a loanword from Latin 'virus' via German or English.