A virus that infects the fungus Aspergillus fumigatus makes the fungus more dangerous by helping it survive stress and resist immune cell attack. When researchers removed the virus from the fungus, it became weaker and less harmful to infected mice. Treating infected mice with an antiviral drug called ribavirin reduced the virus, lowering fungal burden and improving survival, suggesting that targeting fungal viruses could be a new way to treat serious fungal infections.