Most Common Diseases in the World

There are literally millions of diseases and there are many different types of diseases from infectious and contagious diseases to congenital diseases along with acute and chronic diseases. Anything that causes a human pain, distress, social problems or dysfunction can be considered a disease. Injuries and mental disorders are thought to be types of diseases. Some diseases are deadly, while others are no more than an inconvenience under normal circumstances. It can be hard to assess disease numbers, especially in developing countries. Here are some of the most common diseases faced by humans around the world:


Influenza, more commonly called the flu, is largely associated with the seasonal change leading into cooler weather. The flu affects the respiratory tract and has other symptoms that include fever, fatigue, headaches, nasal congestion and body aches. There were a number of large outbreaks that took large tolls on human life during the twentieth century. It is no longer the huge public health risk that it has been in the past, but it is still very common and can be serious.

Hepatitis B

Hepatitis B (HBV) is the most common infectious disease in the world today with two billion people infected. Around 350 million people who contract the virus do not get rid of it. HBV causes an inflammation of the liver and is the most serious of all of the hepatitis strains. It can lead to cirrhosis of the liver as well as liver cancer.


Each year there are around 50 million cases of dengue. It is carried and then spread by Aedes aegypti mosquitoes. Most of the significant outbreaks take place in Asia and Africa. It is rarely fatal, but it can be. Mild cases, which usually affect children have nonspecific symptoms. More moderate cases are characterized by fever, headache, muscle and joint pain and rashes. Dengue hemorrhagic fever results from severe cases. 


Tuberculosis is one of the most deadly contagious diseases, resulting in nearly 2 million deaths per year. The World Health Organization (WHO) has been pushing for more preventative action being taken. The bacteria that causes the disease is most often found in the lungs where it causes severe coughing and bloody phlegm. 

Ischemic heart disease

Coronary artery disease, or ischemic heart disease, is not a contagious disease, but it is still a disease. It is responsible for nearly thirteen percent of all disease fatalities around the world each year. That is around seven million people. It is the leading cause of death in the United States and in other first world countries. It is the gradual narrowing of the coronary artery, which restricts blood flow to the heart. It is cause by plaque build-up, which stems from lifestyle choices, including eating high cholesterol, fatty foods in excess.


Pneumonia itself is not contagious, but it instead results from other contagious diseases or bacterial infections – typically streptococcus or mycoplasma bacteria. The bacteria can live in the body for years waiting for another illness to lower a person’s immunity. The most common pneumonia is streptococcal pneumonia, which is caused by the Streptococcus pneumoniae virus. This variety can be deadly if not treated, it can even lead to meningitis infections.