This document discusses three viruses - Hepatitis B, Hepatitis C, and HIV - that can be transmitted in workplaces and infect people without showing obvious symptoms. It notes that while there are no cures for these viruses, vaccination is available for Hepatitis B and antiretroviral treatment can control HIV infection. The main risks are that these viruses may be present in coworkers or contacts without awareness and can cause fatal diseases since cures are still lacking. Vigilance is needed to avoid transmission.