In theory, a wife can sue her husband's mistress if the husband contracted herpes from the mistress and passed it on to the wife.
In reality, it only works in certain limited situations.
First and foremost, the wife would have to sue the husband. She could include the mistress in that lawsuit, and the husband could also sue the mistress in the same lawsuit. The wife could then keep marching backward in the chain to include the people who passed it on. At some point, it would be too remote and she couldn't go back any further.
This is a tort cause of action. And because tort lawsuits put husband and wife in adversarial roles, this kind of a lawsuit is typically seen in conjunction with divorce cases in which the wife is seeking a disproportionate share of the marital estate.
Here's another point. Personal injury cases are mostly about receiving monetary damages from someone responsible for injuring another. Absent a divorce, you are not going to collect anything from your husband because all of the property is probably community property anyway. There is probably no insurance that will be involved, either for your husband or the mistress. And Texas is a very difficult state to try to collect money damages from an individual.
I hope this answers your question. If there is anything that you do not understand, please let me know and I will be happy to explain further.
In the meantime, please click "Accept" so that I may be paid for my answer and any subsequent follow-ups with you.
The Judge (actively practicing Texas personal injury law attorney and former Trial Court Judge)
P.S. I am frequently asked how someone can specifically request that I, personally, answer a question. Here’s how: for new questions in the future, always begin your question with “QUESTION FOR THE JUDGE.”