A handful of deadly infectious diseases, especially in low-income countries, claim millions of lives worldwide each year: lower respiratory tract infections, diarrheal diseases, HIV/AIDS, tuberculosis, and malaria.
Together, they account for more than one in eight deaths globally. Several of these diseases have plagued humankind throughout history, often decimating populations with greater efficiency than wars.
In an age of vaccines, antibiotics, and dramatic scientific progress, these diseases should have been brought under control. Yet they continue to kill at an alarming rate, particularly in the developing world.
In low-income countries the dominant causes of death are infectious and parasitic diseases (including malaria) and poor medical care surrounding childbirth leading to maternal and neonatal deaths. By contrast, in high-income countries the leading causes of death are non-communicable diseases such as heart disease and cancer. Infectious and parasitic causes of mortality are farther down the list.
Coronavirus disease (COVID-19) is an infectious disease caused by the SARS-CoV-2 virus. Most people infected with the virus will experience mild to moderate respiratory illness and recover without requiring special treatment. However, some will become seriously ill and require medical attention. Older people and those with underlying medical conditions like cardiovascular disease, diabetes, chronic respiratory disease, or cancer are more likely to develop serious illness. Anyone can get sick with COVID-19 and become seriously ill or die at any age.
COVID-19 infections are still rising in 103 countries. There have been at least 293,546,164 reported infections and 5,468,381reported deaths caused by the new coronavirus so far.
A total of 1.5 million people died from tuberculosis (TB) in 2020 (including 214 000 people with HIV). Worldwide, TB is the 13th leading cause of death and the second leading infectious killer after COVID-19 (above HIV/AIDS).
In 2020, an estimated 10 million people fell ill with TB worldwide. 5.6 million men, 3.3 million women and 1.1 million children. TB is present in all countries and age groups. But TB is curable and preventable.
In 2020, 1.1 million children fell ill with TB globally. Child and adolescent TB is often overlooked by health providers and can be difficult to diagnose and treat.
Multidrug-resistant TB (MDR-TB) remains a public health crisis and a health security threat. Only about one in three people with drug resistant TB accessed treatment in 2020.
TB is spread from person to person through the air. When people with lung TB cough, sneeze or spit, they propel the TB germs into the air. A person needs to inhale only a few of these germs to become infected.
When a person develops active TB disease, the symptoms (such as cough, fever, night sweats, or weight loss) may be mild for many months. This can lead to delays in seeking care, and results in transmission of the bacteria to others. People with active TB can infect 5–15 other people through close contact over the course of a year. Without proper treatment, 45% of HIV-negative people with TB on average and nearly all HIV-positive people with TB will die.
Indeed, TB is the leading cause of death worldwide among people infected with HIV. Likewise, among people with latent (inactive) TB infection, HIV infection is the strongest known risk factor for progressing to active TB disease.
Lower Respiratory Tract Infections
Lower respiratory tract infections (including pneumonia) account for more than 4 million deaths worldwide each year—the greatest global killer among infectious diseases. For decades, pneumonia has remained the leading cause of death due to infectious disease around the world.
Pneumonia is a health problem that affects all countries, however, two-thirds of pneumonia deaths are clustered in a diverse group of 20 low-, middle- and high-income countries, notably India and countries in sub-Saharan Africa. In low-income countries, most pneumonia deaths are among children under five years of age, while in high-income countries adults over 70 years of age have the highest mortality rates.
Pneumonia is the leading cause of death of the very young, often striking children with low birth weight or those whose immune system is weakened by malnutrition or other diseases.
Pneumonia kills more children than any other infectious disease, claiming the lives of over 800,000 children under five every year, or around 2,200 every day. This includes over 153,000 newborns. Almost all of these deaths are preventable. The main risk factors include air pollution, a lack of access to water for hand hygiene, and low temperatures. Childhood malnutrition, smoking, exposure to second-hand smoke and low birth weight also have an influence.
Diarrheal diseases are among the top 10 leading causes of infectious disease deaths worldwide. Children under age 5 account for more than half of those deaths. Diarrhea kills 2,195 children every day—more than AIDS, malaria, and measles combined.
Diarrheal diseases account for 1 in 9 child deaths worldwide, making diarrhea the second leading cause of death among children under the age of 5. For children with HIV, diarrhea is even more deadly; the death rate for these children is 11 times higher than the rate for children without HIV. Children die simply because their bodies are weakened—often through rapid loss of fluids and undernourishment. The burden of diarrheal diseases is highest in deprived areas where there is poor sanitation, inadequate hygiene, and unsafe drinking water.
Most diarrheal deaths are preventable using simple, low-cost interventions. Diarrhea causes death by depleting body fluids resulting in profound dehydration. Diarrhea can have a detrimental impact on childhood growth and cognitive development. About 88% of diarrhea-associated deaths are attributable to unsafe water, inadequate sanitation, and insufficient hygiene. Rotavirus is the leading cause of acute diarrhea and causes about 40% of hospitalizations for diarrhea in children under 5. Most diarrheal germs are spread from the stool of one person to the mouth of another. These germs are usually spread through contaminated water, food, or objects.
HIV stands for human immunodeficiency virus, the virus that causes acquired immunodeficiency syndrome (AIDS), the final stage of HIV infection.
In 2020, there were 37.7 million people living with HIV.
680000 million people died from AIDS-related illnesses in 2020.One and half million people became newly infected with HIV in 2020. Since the start of the epidemic,79.3 million people have become infected with HIV .
Unlike most other viruses, HIV attacks the immune system, destroying a type of white blood cell (T cells or CD4 cells) that the immune system needs to fight disease. HIV is transmitted by having sex with someone infected with HIV, by sharing needles and syringes with an infected person, through blood or blood product transfusions, or by being exposed as a fetus or an infant to the virus before or during birth or through breastfeeding. HIV is not transmitted through casual contact such as shaking hands, hugging, modest kissing, or drinking from the same glass.
Malaria is a life-threatening disease caused by parasites that are transmitted to people through the bites of infected female Anopheles mosquitoes. It is preventable and curable. In 2020, there were an estimated 241 million cases of malaria worldwide.
The estimated number of malaria deaths stood at 627 000 in 2020.
Humans infected with malaria parasites can, depending on the type, develop a wide range of illnesses—from mild infection that does not produce symptoms to the classic symptoms of malaria (fever, chills, sweating, headaches, muscle pains) to severe complications (anemia, kidney failure, coma) that can lead to death.
Malaria serves as a particularly dramatic example of infectious disease re-emergence and illustrates the challenges of controlling human vector-borne diseases