In humans, "disease" is often used more broadly to refer to any condition of the body or one of its parts that impairs normal functioning and is typically manifested by distinguishing signs and symptoms. Disease is related to external and internal factors. The emotions are considered the major internal causes of disease in human. Microbes are prime external cause of many human diseases, including measles, whooping cough, chickenpox and meningitis. Health is the freedom from physical disease or pain, while a disordered, weakened or unsound condition is referred to as disease.
Infectious Disease
Infectious diseases are caused by microscopic organisms, such as bacteria, viruses, parasites or fungi when they gain entry into human body, and subsequently grow and multiply. Such disease-causing organisms are known as pathogens. Infectious diseases are the biggest killer of the young. According to Centers for Disease Control and Prevention, "Each year, in the United States, on average 36,000 people die from flu-related complications." This form of disease can be both acute and chronic. The pathogenic microorganisms responsible for infections can be spread from one person to another by means of air, water, food or physical contact.
Non-Infectious Disease
Noninfectious diseases--cardiovascular, cancer, diabetes and arthritis--are caused by nonliving agents. This form of disease cannot be shared from an infectious person to a healthy person. Many non-infectious diseases are caused by nutritional deficiency, environment and genetic inheritances. A group of medical conditions are non-contagious in nature, but do not come under "non-infectious disease"--these include physiological malfunction, and obesity.
Genetic Diseases
A genetic disease is caused by an abnormality in an individual's genome--the genetic material. These abnormalities can be associated with a change in the chromosome numbers--Down syndrome, mutation, or a re-arrangement of genetic information. Genetic disorders may be passed from parent to child or they may occur without a family history. When gene deformities are not inherited from the parents, genetic disorders are caused by changes or mutations that occur in a pre-existing gene or a group of genes.
Nutritional Disorders
A well balanced nutrition plan is necessary for the healthy growth of an individual. Nutritional disorders occur due to malnutrition. Nutritional imbalance also can be caused by mental and physical roles that contribute to the insufficient or excess intake of nutrients by the body. Nutritional deficiency normally leads to problems in thinking and other brain functions as well as in the brain's regulation of the body.
Sexually Transmitted Diseases
Sexually transmitted diseases, including chlamydia, hepatitis, herpes and syphilis, are caused by a group of infectious microorganisms. They can be transferred from one person to another through sexual activity. In the United States, sexually transmitted diseases are the most common infectious disease. AIDS or acquired immune deficiency syndrome is a potentially lethal STD. It is caused by a virus--called HIV, the Human Immunodeficiency Virus. AIDS causes severe damage to the immune system.
