Is it obligatory to inform the girl's family about the presence of latent Hepatitis C virus when proposing to her, knowing that it is only transmitted through blood transfusion?

If an illness is such that it repels people and makes them avoid marrying someone afflicted by it, then it is considered a defect that must be disclosed to the prospective bride. Otherwise, it would be a forbidden deception. Every defect that repels the other spouse and frustrates the purpose of marriage necessitates the option (of annulment). This is supported by the fatwas of the Companions and the Prophet's (peace be upon him) clarification of the defects of prospective spouses. Thus, the correct view is that a defect is anything that frustrates the purpose of marriage, such as pleasure and procreation. Disclosing the defect is hoped to bring about success and good provision.