It's one of only a couple of Caribbean islands to be completely free of malaria and snakes.
Snakes, I don't know for sure--I have noticed them only on Guadeloupe--but it is is not any kind of issue where tourists are being attacked by snakes throughout the Caribbean.
No malaria here in Puerto Rico. We do supposedly have snakes, but no poisonous snakes - and I've never actually seen a snake here, poisonous or not.