What kind of illness does the seller have a duty to disclose under Texas law?

The correct answer reflects Texas law's specific treatment of certain illnesses in the context of a seller’s disclosure obligations. In Texas, while sellers have a duty to disclose material defects that could affect a purchaser's decision, they are not required to disclose certain health conditions, including an HIV infection. This aligns with guidelines that balance privacy rights of individuals with the necessity for transparency in sales transactions.

This legal framework recognizes that disclosing personal medical information, particularly regarding conditions like HIV, may infringe on an individual's right to privacy without contributing material information to the buyer. Hence, sellers are generally not compelled to report such health conditions, which might be considered confidential and not directly affecting the property or transaction at hand.

The other options imply obligations for the seller to disclose various illnesses, which exceeds the actual requirements established under Texas law. In particular, suggesting a blanket requirement to disclose all illnesses or only major medical conditions overlooks the careful consideration of personal privacy entrenched in state regulations.