Emerging infectious diseases part 1

At the turn of the 20th century, life expectancy was below 50 years, largely due to infectious diseases. Doctors had limited tools, offering only sympathy as 25% of mothers died during childbirth from bacterial infections, and child mortality was high. Diseases like cancer and Alzheimer's were less common as people did not live long enough to develop them. Historically, diseases, not war, have dictated major demographic shifts. For instance, more soldiers died of infection than combat in the American Civil War.

The late 19th and early 20th centuries marked a 'golden age' for bacteriology, virology, and immunology, leading to the development of vaccines and antibiotics. These advancements dramatically reduced infectious disease deaths in developed nations, increasing life expectancy by 20% in 30 years. However, this progress is fragile, as demonstrated by the 1918 influenza pandemic, which significantly reduced life expectancy.

Despite overall progress, a significant gap in life expectancy persists between rich and poor countries. Third-world nations, particularly in sub-Saharan Africa, faced a severe setback due to the HIV/AIDS pandemic, with life expectancy plummeting to 1950s levels. Currently, HIV/AIDS, tuberculosis, and malaria continue to kill millions annually, primarily in sub-Saharan Africa. While drugs exist for these diseases, an additional $6 billion is needed for full medical treatment in Africa, a sum equivalent to the annual advertising budget for flavored soda or two weeks of the Iraq War, highlighting skewed global priorities.

A critical turning point for global health funding was the establishment of the Bill and Melinda Gates Foundation in 2000. This initiative channeled billions of dollars towards vaccinations and treatments for diseases like HIV, making them more accessible in affected regions. Others, like Warren Buffett, also contributed substantially, fostering a trend where even governments of wealthy nations increased their aid. David Cameron, then UK Prime Minister, doubled Britain's commitment to polio eradication, highlighting vaccination as a cost-effective and transparent way to save lives, emphasizing the importance of global collaboration and self-interest in preventing global problems from reaching one's doorstep.

Microbes have had a historical impact comparable to wars and economic crises. While 19th-century science viewed microbes primarily as enemies, leading to hygiene and antibiotic development, it's now understood that most microbes are not pathogenic and are vital for multicellular organisms. The human body, with its trillions of cells, also hosts trillions of microbes, most of which are beneficial, aiding digestion, immune system development, and protection against pathogens. An imbalance in this microbiota can lead to serious health issues like obesity, autoimmune diseases, and mental conditions.

Newborns acquire their first microbes during delivery. Vaginal births expose infants to the mother's vaginal microbiota, which is crucial for establishing a healthy microbial community. Babies born via C-section, however, bypass this exposure, leading to a different microbiota composition, potentially increasing the risk of diseases like asthma and autoimmune conditions. A simple procedure of exposing C-section babies to maternal vaginal microbes immediately after birth can restore a more normal microbiota, showing positive effects a year later.

Microbiology is a vast field, impacting nearly every aspect of human life. Microorganisms are essential in agriculture for waste breakdown and nitrogen fixation, in environmental remediation for treating sewage and decomposing waste, and in food production for cheese and bread. They synthesize essential vitamins in our intestines and help herbivores digest cellulose. Crucially, microbes maintain environmental balance by recycling vital nutrients like nitrogen, sulfur, phosphorus, carbon, and oxygen. Marine microbes, especially algae and cyanobacteria, produce 50% of the oxygen we breathe, making them indispensable for life on Earth.

Microbes have been instrumental in enabling agricultural societies for 10,000 years, producing wine, bread, and cheese. Beyond food, the normal microbiota on our skin and other body parts protects against more harmful microbes. Antibiotics, while targeting pathogens, can also eliminate beneficial bacteria, leading to secondary infections that can be more severe than the initial illness. Microbes are also used in drug development, like penicillin from mold, and in genetic engineering to produce human proteins like insulin, which was previously extracted from animal pancreases.

The evolution of microbes is intricately linked to human evolution. Many microbes are adapted to infect humans, thriving at our body temperature. Both humans and microbes need each other for survival, striving for a coexistence where the microbe ideally keeps its host alive and healthy. Severe diseases, such as smallpox or Ebola, often represent an accidental failure of this equilibrium, where rapid host death compromises the microbe's survival. In contrast, successful pathogens like tuberculosis cause chronic diseases that allow for long-term transmission.

Ebola, an aggressive virus that quickly kills its host, is less successful in spreading broadly compared to more chronic infections. Its outbreaks are geographically limited. Similarly, SARS in 2003, with a 10% lethality rate, disappeared quickly, struggling to spread due to its aggressiveness. MERS, even more aggressive with a 35% lethality, also had limited spread. COVID-19, with a lower lethality rate of approximately 1%, is set to persist because its less aggressive nature allows it to spread more easily among hosts, reflecting the principle that microbial natural selection favors less virulent strains for broader dissemination.

Despite their beneficial roles, some microbes have caused immense devastation. Smallpox, present for 4,000 years, killed 300 million people in the 20th century alone. The Spanish flu of 1918-1919 claimed 50 to 100 million lives when the global population was less than two billion. The bubonic plague, caused by Yersinia pestis, reduced Europe's population by a third in the 14th century, decreasing the world's population by over 100 million. These historical pandemics highlight how social and economic factors, such as rapid urbanization and poor sanitation, exacerbated disease spread. While modern antibiotics can treat the bubonic plague, the impact of these three microbes on human history remains astounding.