Disease. What is?

Disease

Disease can be :

1. Infectious
2. Deficiency
3. Genetic
4. Mental

1. Infectious disease- are caused by pathogenic microorganisms and has the ability to spread quickly, directly, or indirectly. Infectious disease is an invasion of a host organisms by foreign organisms, often called microbes (small and microscopic). Microbes ( example viruses, bacteria). An organism that microbe infects is called the host. Infectious disease is transmitted by a vector (i.e. agent by means of mode transfer).

2. Deficiency disease is caused by lack of a certain nutrient in a person's body. In this case a person'd diet is short of an essential nutrient. Xerophthalmia (night blindness) is a deficiency disease caused by a deficiency of vitamin A (retinal) in the diet.

3. Genetic disease is a disorder that is inherited genetically. A genetic disease is as a result of a mutation in an individual's DNA, as a result of a change in letter in a person's DNA sequence. Genetic disease can be inherited because of a mutation of gene cells in the body. This can happen when cells pass gene information from parent to offspring or by mutation of DNA sequence in a single gene. For example, sickle cell anemia is a mutated form of hemoglobin that distort the shape of the red blood cell, so it appears sickle (crescent) in shape.

4. Mental disease is a disease of the mind generally  associated with distress or disability. It is a medical condition that disrupts the way a person thinks, feel and behave. An example is depression, which is a condition of mental disturbance. The person may have difficulty in maintaining concentration or interests to life causing a feeling of sadness.