Disease is a deviation from the normal functioning of the body which impairs health. Diseases manifest in the forms of symptoms and signs. There are infectious diseases and non-infectious diseases. Infectious diseases occur due to the invasion of pathogens like bacteria, viruses and protozoans in to the human body. They spread from one person to another by means of air, food, water, contact and also through carriers called as vectors. Genetic diseases, cardiac diseases, hormonal imbalances, malignancies and all come under the category of non-infectious diseases. The abnormal conditions that require medical attention are also termed as diseases. A person can be in a good medical condition or in a diseased condition. Physiological conditions are also there which require medical attention.