A disease is a pathological condition of a part, organ or system of an organism resulting from various causes like genetic defect, infection and environmental stress. It is characterized by an identifiable group of symptoms.

Here is the 10 most deadly diseases in the world, according to the World Health Organization(WHO).

10) Tuberculosis

Tuberculosis (TB) is a bacterial infection that affects the lungs; it can also spread to other organs of the body. It is an unpredictable disease. In some cases the disease remains stagnant while in others it wreaks havoc straight away.

9) Hypertensive Heart Disease

This disease can lead to a number of cardiac complications, and even a heart failure and death. It is basically the formation of high blood pressure. The person affected by this disease generally experiences hypertension.

8) Diabetes Mellitus

This disease occurs when the pancreas is unable to create enough insulin for the body to use (type-1 diabetes), or when the body loses its capacity to use the insulin produced by the pancreas (type-2 diabetes).

7) Diarrhea

This disease does not last for more than two or three days; however, in some cases, it could last weeks or even a month. The person affected by this disease passes watery stool. Diarrhea causes dehydration, due to which the body loses essential electrolytes and fluids.

6) AIDS

Acquired immunodeficiency syndrome (AIDS) is caused by human immunodeficiency virus (HIV). This disease weakens the immune system. The virus attacks the T cells and CD4 cells in the human bloodstream. As of now there is no cure for this deadly disease.

5) Lung cancer

Lung cancer is the uncontrolled growth of abnormal cells that start off in one or both lungs; usually in the cells that line the air passages. People who smoke are more likely to be affected by this deadly disease.

4) Lower respiratory infections (bronchitis and pneumonia)

Lower respiratory infections are mainly of two kinds: bronchitis and pneumonia. They affect the person’s ability to breathe normally. Symptoms of these diseases are sore throat, runny nose, headache and sneezing. It is not easy to diagnose these diseases.

3) Chronic obstructive pulmonary disease (COPD)

Chronic obstructive pulmonary disease is a common lung disease. It has a huge negative impact on the person’s respiratory system. There are two types of COPD: chronic bronchitis and emphysema. Smoking and pollution are the main causes of COPD.

2) Stroke (Cerebrovascular accident)

Stroke  is a medical emergency. Sometimes referred to as a cerebrovascular accident (CVA), cerebrovascular insult (CVI) or colloquially brain attack, this disease is the loss of brain function due to a disturbance in the blood supply to the brain.

1) Ischemic heart disease

Ischemia means a reduced blood supply. This disease is characterized by reduced blood supply to the heart. It is the most common cause of death in most western countries. This disease is usually caused by atherosclerosis, present even when the artery lumens appear normal by angiography.