Perhaps he is healthy enough not to have any adverse reactions? Has he ever done a parasite cleanse? I would say that he probably is so healthy that his body can handle any detox reactions with ease. My husband did a para cleanse and he didn't have any symptoms either and I know that man is riddled with parasties only because he lives on sugar, it's not normal the amount of sugar he consumes daily! He eats out six days a week during lunch and he drinks a six pack of coke daily...not that is your husband but I would have thought mine had some sort of die off but none. The men in my life are of strong constitution but don't plan for the hidden dangers of the excesses they indulge in.
Some people don't show any signs of any issues and have things brewing that are not so noticeable. I think women's bodies are more sensitive to most things and for good reason, we give life and our bodies have to be running well to do so. I have a book here somewhere, can't recall off hand but in this book the scientist said that women absorb 50% more toxins from the environment than a man's body. Perhaps it's due to the higher fat content of our bodies vs. the leaner muscle or it could be that women are to avoid those things because our bodies having to be healthy enough to giving life. (?) The book was a bit over my head because it was pretty scientific but it did have some good info I could understand.
Then again maybe he just doesn't have them. = ) Do you have pets?

Die-off symptoms depend on the severity of the infection and the health of the person. If he had no noticible symptoms before he started the cleanse, then'll he probably won't have any die-off symptoms. He is just now into the cleanse and might show signs later, BUT - HUMAWORM is formulated to be very strong yet gentle on the body. 70% of all parasites that infect humans are microscopic and only 30% are visible - AND of that 30% most are small and look very different in real life than what you'd expect. I am glad he's doing well!