Iranians observe cleanliness in public and private because of their belief. Many campaigns have organized for vaccinations and trainings especially in rural places to prevent diseases and accurate cure. There is no especial current disease in Iran that may be dangerous to you.
There have been overwhelming campaigns, like vaccinations and trainings, to eliminate many diseases used to exist in remote settlements. It has been a success and today you see clean streets, restaurants, hotels, shops, supermarkets, parks, etc.
High medical standards with most doctors speaking English: consultation fees cheap. Plenty of pharmacies with ultra cheap prices on generic medicine. There is a slight malaria risk depending on the location and time of year. In extreme summer heat, dehydration is of course a danger. On the plus side, tap water is safe to drink almost everywhere.