Globalization, the flow of information, goods, capital, and people across political and geographic boundaries, allows infectious diseases to rapidly spread around the world, while also allowing the alleviation of factors such as hunger and poverty, which are key determinants of global health. The spread of diseases across wide geographic scales has increased through history. Early diseases that spread from Asia to Europe were bubonic plague, influenza of various types, and similar infectious diseases.
In the current era of globalization, the world is more interdependent than at any other time. Efficient and inexpensive transportation has left few places inaccessible, and increased global trade in agricultural products has brought more and more people into contact with animal diseases that have subsequently jumped species barriers (see zoonosis).
Globalization intensified during the Age of Exploration, but trading routes had long been established between Asia and Europe, along which diseases were also transmitted. An increase in travel has helped spread diseases to natives of lands who had not previously been exposed. When a native population is infected with a new disease, where they have not developed antibodies through generations of previous exposure, the new disease tends to run rampant within the population.
Etiology, the modern branch of science that deals with the causes of infectious disease, recognizes five major modes of disease transmission: airborne, waterborne, bloodborne, by direct contact, and through vector (insects or other creatures that carry germs from one species to another). As humans began traveling overseas and across lands which were previously isolated, research suggests that diseases have been spread by all five transmission modes.
Travel patterns and globalization The Age of Exploration generally refers to the period between the 15th and 17th centuries. During this time, technological advances in shipbuilding and navigation made it easier for nations to explore outside previous boundaries. Globalization has had many benefits, for example, new products to Europeans were discovered, such as tea, silk and sugar when Europeans developed new trade routes around Africa to India and the Spice Islands, Asia, and eventually running to the Americas.
In addition to trading in goods, many nations began to trade in slavery. Trading in slaves was another way by which diseases were carried to new locations and peoples, for instance, from sub-Saharan Africa to the Caribbean and the Americas. During this time, different societies began to integrate, increasing the concentration of humans and animals in certain places, which led to the emergence of new diseases as some jumped, in mutation, from animals to humans.
During this time sorcerers' and witch doctors' treatment of disease was often focused on magic and religion, and healing the entire body and soul, rather than focusing on a few symptoms, in the way modern medicine does. Early medicine often included the use of herbs and meditation. Based on archaeological evidence, some prehistoric practitioners in both Europe and South America used trephining, making a hole in the skull to release illness. Severe diseases were often thought of as supernatural or magical. The result of the introduction of Eurasian diseases to the Americas was that many more native peoples were killed by disease and germs than by the colonists' use of guns or other weapons. Scholars estimate that over a period of four centuries, epidemic diseases wiped out as much as 90 percent of the American indigenous populations.
In Europe during the age of exploration, diseases such as smallpox, measles and tuberculosis (TB) had already been introduced centuries before through trade with Asia and Africa. People had developed some antibodies to these and other diseases from the Eurasian continent. When the Europeans traveled to new lands, they carried these diseases with them. (Note: Scholars believe TB was already endemic in the Americas.) When such diseases were introduced for the first time to new populations of humans, the effects on the native populations were widespread and deadly. The Columbian Exchange, referring to Christopher Columbus's first contact with the native peoples of the Caribbean, began the trade of animals, and plants, and unwittingly began an exchange of diseases.
Evolution of germ theory It was not until the 1800s that humans began to recognize the existence and role of germs and microbes in relation to disease. Although many historical thinkers had ideas about germs, it was not until French doctor Louis Pasteur spread his theory about germs, and the need for maintaining sanitation (particularly in medical practice), that the majority of people listened. The idea of sanitation was based on earlier research by Ignaz Semmelweis in Austria in 1847, who proved that doctors' hand washing and sterilisation with chlorine prevented clinic-based deaths of mothers, that were occurring due to infectious puerperal fever and sepsis, after childbirth. Even earlier than this, Samuel Hahnemann, the founder of homoeopathic medicine, had in the late 18th Century, developed and published sound guidelines for quarantine, washing, ventilation and other public health measures to limit the spread of disease. Later, by 1796, Hahnemann had begun developing homoeopathic vaccination for scarlet fever and other diseases, and by 1831 he had clearly outlined his theory of germ-based causation in the cholera epidemic. Edward Jenner also introduced an effective smallpox vaccine in 1796-1798, based on exposure (by inoculation) to the less virulent cowpox, an idea that had already been proposed by others. Jenner, whose understandings developed over time, used a method not dissimilar to homoeopathy in principle. Furthermore, Hahnemann developed a ground-breaking scientific research method based on work in Austria, that is still adhered to today by medical researchers.
Many people remained skeptical of this "infectious micro-organism" ("germ") concept, due to prevailing beliefs about diseases being caused by "miasma", and later by more general ideas of sanitation. Pasteur persuasively demonstrated the validity of a germ theory of disease, and on May 22 1881, he set out to prove an early example of veterinary vaccination. The anthrax vaccine was administered to 25 sheep while another 25 were used as a control. On May 31 1881, all of the sheep were exposed to anthrax. While every sheep in the control group died, each of the vaccinated sheep survived. Pasteur's experiment would become a milestone in conventional disease prevention. His findings, in conjunction with other vaccines that followed, changed the way that the globalization of ideas in medicine affected the world.
Effects of globalization on disease in the modern world Modern modes of transportation allow more people and products to travel around the world at a faster pace; they also open the airways to the transcontinental movement of infectious disease vectors. One example is the West Nile virus. It is believed that this disease reached the United States via "mosquitoes that crossed the ocean by riding in airplane wheel wells and arrived in New York City in 1999." With the use of air travel, people are able to go to foreign lands, contract a disease and not have any symptoms of illness until after they get home, and having exposed others to the disease along the way. Another example of the potency of modern modes of transportation in increasing the spread of disease is the 1918 Spanish Flu pandemic. Global transportation, back in the early 20th century, was able to spread a virus because the network of transmittance and trade was already global. The virus was found on crew members of ships and trains, and all the infected employees spread the virus everywhere they traveled. As a result, almost 50-100 million people died of this global transmission.
As medicine has progressed, many vaccines and cures have been developed for some of the worst diseases (plague, syphilis, typhus, cholera, malaria) that people develop. But, because the evolution of disease organisms is rapid, even with vaccines, there is difficulty providing full immunity to many diseases. Since vaccines are made partly from the virus itself, when an unknown virus is introduced into the environment, it takes time for the medical community to formulate a curative vaccine. The lack of operational and functional research and data, which provide a quicker and more strategized pathway to a reliable vaccine, makes for a lengthy vaccine development timeline. Even though frameworks are set up and preparations plans are utilized to decrease the COVID-19 cases, a vaccine is the only broadly accepted way to ensure complete immunization. Some systems like the IIS, Immunization Information System, help give preliminary structure for quick responses to outbreaks and unknown viruses. These systems employ past data and research-based on modern world vaccine development successes. Finding vaccines at all for some diseases remains extremely difficult. Without vaccines, the global world remains vulnerable to infectious diseases.
Evolution of disease presents a major threat in modern times. For example, the current "swine flu" or H1N1 virus is a new strain of an old form of flu, known for centuries as Asian flu based on its origin on that continent. From 1918 to 1920, a post-World War I global influenza epidemic killed an estimated 50–100 million peens, including half a million in the United States alone.Dorothy A. Pettit and Janice Bailie, Before There Was Swine Flu; Anne Sealey, Review: "A Cruel Wind: Pandemic Flu in America, 1918–1920" , eHistory, July Review, 2009; Ohio State University, accessed 26 Jan 2010 H1N1 is a virus that has evolved from and partially combined with portions of avian, swine, and human flu.
Globalization has increased the spread of infectious diseases from South to North, but also the risk of non-communicable diseases by transmission of culture and behavior from North to South. It is important to target and reduce the spread of infectious diseases in developing countries. However, addressing the risk factors of non-communicable diseases and lifestyle risks in the South that cause disease, such as use or consumption of tobacco, alcohol, and unhealthy foods, is important as well.
Even during pandemics, it is vital to recognize economic globalization in being a catalyst in the spread of the coronavirus. Economic factors are especially damaged by increased global lockdown regulations and trade blockades. As transportation globalized, economies expanded. Internalized economies saw great financial opportunities in global trade. With increased interconnectivity among economies and the globalization of the world economy, the spread of the coronavirus maximized the potentiality of global recessions. The coronavirus pandemic caused many economic disruptions, which caused a functional disconnect in the supply chain and the flow of goods. As transportation modes are relevant to the spread of infectious diseases, it is important to also recognize the economy being the motor of this globalized transmission system.
Specific diseases
Plague