Are you sure on the "don't breathe?" Don't mosquitoes detect gases in breath?

A friend of mine is a biologist researching mosquitos. He travelled twice a year to the Amazon to catch mosquitos for his research and his method was exposing a leg and catch them while they bite him. He ended up like 4 or 6 months on the hospital with malaria, a couple of months after release he relapsed again, it didn't made medical sense for it, so they checked him and he had cancer. Another year of medical treatments and got better. He looks 10 years after all of that, but got a permanent position as a professor and he's still researching mosquitos but now is other people going to the Amazon to capture them.