This is the 158th most frequent Slovenian word.
virusa
"Virusa" in Slovenian means "of the virus" (genitive singular form of "virus").
Here, 'virus' is the subject doing the action of spreading.
Virus je hitro razširil svoje delovanje.
The virus quickly spread its activity.
In this context, 'virusa' functions as an object in the genitive case, describing samples related to the virus.
Laboratorij preučuje vzorce virusa.
The laboratory is studying the virus samples.
'Virusa' appears as a genitive case noun, indicating cause or reason in this sentence.