Compiling a list of the most common diseases in the world can be a difficult task. Disease generally refers to infectious disease, but it may also include chronic disease, genetic disorders, and pathologies such as cancer.
Also, how common a disease is may vary by geography, gender, age group, and environmental or hereditary factors.
Most common infectious diseases
According to the World Health Organization (WHO)’s 2009 World Health Statistics, three out of every 10 deaths is due to a communicable (or infectious) disease. Infectious diseases are more common in developing parts of the world, but they don’t recognize borders.
HIV/AIDS – The prevalence of AIDS is highest in Africa, but the disease, which is caused by infection with human immunodeficiency virus (HIV) is found worldwide, affecting more than 30 million people. According to the WHO, in 2007, AIDS had a cause-specific mortality rate of 1049 per 100,000 population, five-times the rate of malaria.
Malaria – Malaria is caused by infection with a parasite carried by mosquitoes. The Centers for Disease Control (CDC) estimates that 219 million people were infected in 2010, leading to more than 660,000 deaths, most of them in Africa. Programs aimed at eradicating mosquitoes in the mid-20th century led to the declaration of the United States as being malaria-free in 1949.
Tuberculosis – Tuberculosis is a respiratory infection with Mycobacterium tuberculosis. This diseases was once the leading cause of death in the United States. According to the WHO, the disease has seen a resurgence in recent years in Europe and Africa, despite better treatments, and likely due to the increased longevity of HIV patients. The bacterium damages the lungs and other organs, leading to more than 1 million deaths worldwide each year according to the WHO.
Most common genetic diseases
Genetic diseases are caused by mutations in a person’s DNA. The mutations may be in genes or due to chromosomal abnormalities. Genetic Alliance UK estimates that 5.5% of the population will find that they have a genetic disorder by the time they are 25 years old. The most common genetic diseases are inherited in an autosomal dominant pattern, but autosomal recessive and X-linked genetic disorders also affect the population worldwide.
Familial combined hyperlipidemia and familial hypercholesterolemia are two autosomal dominant disorders that result in excess fatty substances accumulating in the blood (lipids in the first and cholesterol in the second). They occur in 5 and 2 out of every 1000 births, respectively. They result in atherosclerosis and heart disease.
The most common autosomal recessive genetic disorder is cystic fibrosis, which affects 0.4 per 1000 births according to Genetic Alliance UK, which amounts to 70,000 children and adults worldwide according to the Cystic Fibrosis Foundation. Cystic fibrosis affects the pancreas and lungs, leading to fluid accumulation in the respiratory system and breathing and digestion problems.
Finally, according to Genetics Alliance UK, the most common X-linked genetic disorder is Fragile X syndrome. This genetic abnormality affects males more than females and leads to cognitive decline and developmental issues. According to the National Library of Medicine, Fragile X affects one in 4000 males and one in 8000 females.
Most common non-communicable diseases
According to the WHO’s report, non-communicable diseases are responsible for more deaths than any other form of disease, and the CDC cites chronic disease as the most common cause of mortality among American (7 out of every 10 deaths). Half of these deaths are due to heart disease, cancer and stroke.
Heart disease – The term “heart disease” generally refers to coronary artery disease. This is a blockage of the arteries that feed the heart, leading to a heart attack. The CDC estimates that heart disease kills 600,000 people in the United States each year, and 715,000 Americans have a heart attack each year.
Stroke – Stroke is similar to heart disease, but it is a blockage of the arteries feeding the brain. The National Stroke Association cites stroke as the fourth leading cause of death and disability in the United States, with more than three-quarters of a million strokes occurring each year, and more than seven million stroke survivors over the age of 20 years living in the United States.
Cancer – According to the CDC, lung cancer is the most common cause of cancer death, but the most common type of cancer is actually prostate cancer according to the National Cancer Institute. A total of 238,000 new cases of prostate cancer are expected in the United States this year (2013), but less than 30,000 deaths are expected. In contrast lung cancer is expected to be diagnosed in about 228,000 people and results in more than 159,000 deaths.
Compiling the list
The most common diseases in the world include AIDS, malaria, heart disease, cancer and genetic disorders, but their causes and effects are very different, making it difficult to directly compare them. However, when looking at the number of people affected and the mortality rates for these various diseases, the hundreds of millions of people affected by malaria and the millions who die from tuberculosis put them at the top of the list.
