I recommend to start with bottled water for the first week. There are no poisonous insects or snakes although there is a Loxosceles spider that lives inside old houses and can give a nasty bite when is bothered. There are mosquitos in some places, however they do not carry diseases. The sun is strong and sensible measures should be taken. If you are planning to travel high in the Andes, especially over 3500 mts above sea level, perhaps you should contact a local phycician to give advice and some pills to avoid mountain sickness.
Most doctors speak English there and they have all specialties.
Although a safe place, always common sense measures should be taken. Avoid showing money, use traveller cheques, do not take all your money in the same place, have passport photocopies in your luggage, girls should travel accompanied and dressed. If you are fined for speeding do not attempt offering money to the Police as you can end spending the night behind bars. The Police are called Carabineros and they are extremely helpful. They are not corrupt.