The Perfect Murder?

Apparently, (presumably) a man can eat a Brazil nut and then that man can inseminate a woman, or presumably another man, who is allergic to Brazil nuts, which will, in fact, effect the woman's nut allergy.

People who are allergic to Brazil nuts have a unique problem, it’s the only allergic reaction known to be sexually transmissible. In other words, the semen of a man who has eaten brazils can trigger an allergic response if a sexual partner of his who has an allergy.

What a way to murder someone?

It makes a great premise for a story, I reckon. I guess, if the partner was known to have known that their partner had a nut allergy, it could be proven it was deliberate. But, what about a hired killer?