There are not much viruses in the Sierra. On that point of view, Ecuador isn’t more dangerous than other tropical regions. But if you are planning to travel to the warm-tropical regions (jungle, Pacific coast: specially the Esmeralda’s county, northwest of Ecuador) it is recommendable to get a vaccination against Malaria. Please note: For the protection of indigenous peoples, proof of a yellow-fever vaccination must be shown when visiting some areas of the Amazon basin. Ask your doctor about this and other vaccinations before you start your trip. People that have high pressure or suffer from heart and blood circulation troubles also have to consult a doctor, respect the influence that the altitude and the tropic zone have in their health. There are good doctors in Quito that can handle with all type of illnesses and accidents, also several hospitals and emergency stations. The most modern hospital in Quito is the “Metropolitano”.
English speaking physicians, and specialists are available - so don't worry about your medical needs.