What's so weird about assuming that it was spread by people making whoopee with monkeys? That sounds almost normal compared to some sexual appetites in the proccess of being main streamed these days.
I would bet that 'monkey' would resist such, if capable (I know, don't go there.): 'monkeys' have better taste...
...and may 'taste better': fwiw, my bet is on the bushmeat/butchering connection, which has been postulated as a vector for Marburg and Ebola as well.