i play with my wife's ass primarily with my fingers to get her off and i make it a point not to use the same ones in her ass as i do in her pussy. we both make sure that we wash all contact points after we are done. we have been doing this for over 20 years and we have never had any known problems with this type of play. on a few occasions i have gone from pussy to ass when we were having intercourse but only once the other way and she was not happy about it so i have never gone that way again. we have never had a problem with that either. just passing along my personal experience for others to consider.