Globalization, the flow of information, goods, capital and people across political and geographic boundaries, has also helped to spread some of the deadliest infectious diseases known to humans. The spread of diseases across wide geographic scales has only increased through history. 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).
It is believed that globalization began during the Age of Exploration. An increase in travel also helped spread diseases to natives of land who had not previously been exposed. When a native population is infected with a new disease, where no antibodies have been developed, the 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 over seas and across lands which were previously isolated research suggests that diseases have been spread by all five transmission modes.
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 into the Americas. In addition to trading in goods, many nations began to trade in slavery. Trading in slaves helped to introduce new diseases to new locations. During this time, different societies began to integrate, increasing the concentration of humans and animals in one place, and led to the emergence of new diseases.
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 like modern medicine. Early medicine often included the use of herbs, and meditation, and sometimes even trephining Severe diseases were often thought of as supernatural or magical. As a result, the destruction of the native peoples are more attributable to germs than to gunpowder. 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 and tuberculosis had been around for centuries and people had developed antibodies to these and other diseases. When the Europeans traveled to new lands they carried these diseases with them. When these 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.
Humans began to recognize the fact that germs and microbes exist in the 1800’s. Although, many scientists had ideas about germs through history, it wasn’t until Louis Pasteur spread his theory about germs, and the need for washing hands and sanitation (particularly in medical practice) that anyone listened. Many people were quite skeptical, but on May 22, 1881 Pasteur persuasively demonstrated the validity of his germ theory of disease with the first successful vaccination. The anthrax vaccine was administered to 25 sheep while another 25 was used as a control. On May 31, 1881 all of the sheep were exposed to anthrax. While all of the sheep in the control group died, all of the vaccinated sheep remained alive. Pasteur’s experiment would become a milestone in disease prevention. His findings, in conjunction with other vaccines that followed, changed the way globalization affected the 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 of this occurring is 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 they get home, having exposed others to the disease along the way.
As medicine has progressed, many vaccines and cures have been developed for some of the worst diseases (plague, syphilis, typhus, cholera, malaria) the world has encountered. However, because the evolution of disease organisms is very rapid, even with vaccines we have difficulty providing full immunity to many diseases, and finding vaccines at all for some diseases remains extremely difficult. Without vaccines our 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 on an old form of flu. H1N1 is a virus that has evolved from and partially combined with portions of avain, swine, and human flu.
Globalization not only increased the spread of infectious diseases from South to North, but also the risk of non-communicable diseases 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-comunnicable diseases, such as tobacco, alcohol, and unhealthy foods, in the South is important as well. 
Bubonic plague is a variant of the deadly flea borne disease plague, which is caused by the enterobacteria Yersinia pestis, that devastated human population beginning in the 14th century. Bubonic plague is primarily spread by fleas who lived on the common black rat. A human would become infected after being bitten by an infected flea. The first sign of an infection of bubonic plague is swelling of the lymph nodes, and the formation of buboes. These buboes would first appear in the groin or armpit area, and would often ooze pus or blood. Eventually infected individuals would become covered with dark splotches caused by bleeding under the skin. The symptoms would be accompanied by a high fever, and within four to seven days of infection more than half the victims would die. During the 14th and 15th century, humans did not know that a bacterium was the cause of plague, and efforts to slow the spread were futile.
The first recorded outbreak of plague occurred in China in the 1330s, a time when China was engaged in substantial trade with western Asia and Europe. The plague struck Europe in October 1347. It was thought to have been brought into Europe through the port of Messina, Sicily, by a fleet of Genoese trading ships from Kaffa, a seaport on the Crimean peninsula. When the ship left port in Kaffa, many of the inhabitants of the town were dying, and the crew was in a hurry to leave. By the time the fleet reached Messina, all the crew were either dead or dying; and the rats they were carrying had slipped unnoticed to the shore.
Within Europe, the plague struck port cities first, then followed both sea and land trade routes. It raged through Italy into France and the British Isles, and was carried over the Alps into Switzerland, and eastward into Hungary and Russia. For a time during the 14th and 15th centuries the plague would recede, but every ten to twenty years it would return. Later epidemics however, were never as widespread as earlier outbreaks.
Plague has never died out, and from 1896-1918 the Plague swept through India taking the lives of over 12.5 million people. Between 1906 and 1914 the Plague Research Commission was created, and published supplements to the Journal of Hygiene
Measles is a highly contagious airborne virus that is spread by contact with infected oral and nasal fluids. When a person with measles coughs or sneezes they release microscopic particles into the air. During the 4-12 day incubation period an infected individual will show no symptoms, but as the disease progresses the following symptoms will appear; runny nose, cough, red eyes, extremely high fever and a rash.
Measles is an endemic disease, meaning that it has been continually present in a community, and many people develop resistance. In populations that have not been exposed to measles, exposure to a new disease can be devastating. In 1529, a measles outbreak in Cuba killed two-thirds of the natives who had previously survived smallpox. Two years later was responsible for the deaths of half the population of Honduras, had ravaged Mexico,Central America, and the Inca civilization.
Historically, measles was very prevalent throughout the world, as it is highly contagious. According to the National Immunization Program, 90% of people were infected with measles by age 15. Until the vaccine was developed in 1963, measles was considered to be deadlier than smallpox. Vaccination reduced the number of reported by 98%, and major epidemics have predominantly occurred in unvaccinated populations, particularly nonwhite Hispanic and African American children under 5 years old. In 2000 a group of experts determined that measles was no longer epidemic in the United States, and the majority of cases that occur there are in people immigrating from other countries.
Typhus is caused by rickettsia, which is transmitted to humans through lice. The main vector for typhus is the rat flea. Flea bites and infected flea feces in the respiratory tract are the two most common methods of transmission. In area where rats are not common, typhus may also be transmitted through cat and opossum fleas. The incubation period of typhus is 7–14 days. The symptoms start with a fever, then headache, rash and eventually stupor. Spontaneous recovery occurs in 80-90% of victims.
The first outbreak of typhus was recorded in 1489, when it is believed that troops from the Balkans, hired by the Spanish army brought it to Spain with them. By 1490 Typhus traveled from the eastern Mediterranean into Spain and Italy and by 1494 it had swept across Europe. More soldiers were killed from 1500-1914 by typhus than from all military action during that time combined. Finally, during World War I, preventative delousing measures were instituted, and the disease began to decline. The creation of antibiotics has allowed disease to be controlled within two days of taking a 200 mg dose of tetracycline.
Syphilis is a sexually transmitted disease that causes open sores, delirium and rotting skin, and is characterized by genital ulcers. Syphilis can also do damage to the nervous system, brain and heart. The disease can also be transmitted from mother to child.
The origins of syphilis are unknown, and some historians argue that it descended from a twenty-thousand-year-old African zoonosis. Other historians place its emergence in the New World, arguing that the crews of Columbus’s ships first brought the disease to Europe. The first recorded case of syphilis occurred in Naples in 1495, after King Charles VIII of France besieged the city of Naples, Italy. The soldiers, and the prostitutes who followed their camps, came from all corners of Europe. When they went home, they took the disease with them.
Smallpox is a highly contagious disease caused by the Variola virus. There are four variations of smallpox; variola major, variola minor, haemorrhagic, and malignant, with the most common being variola major and variola minor. Symptoms of the disease including hemorrhaging, blindness, back ache, vomiting, generally occur shortly after the 12-17 day incubation period. The virus then begins to attack skin cells, and eventually leads to an eruption of pimples that cover the whole body. As the disease progresses the pimples will fill up with pus or merge together. This merging results in a sheet that can detach the bottom layer from the top layer of skin. The disease is easily transmitted through airborne pathways (coughing, sneezing, and breathing) as well as through contaminated bedding, clothing or other fabrics,
Smallpox was a common disease in the 15th century, and was spread by explorers and invaders. After Columbus landed on the island of Hispaniola, during his second voyage in 1493, local people started to die of a virulent infection. Before the smallpox epidemic started more than one million people had lived on the island; after only ten thousand had survived.
In 1617, Smallpox reached Massachusetts and came with earlier explorers, probably by way of Nova Scotia, Canada.” By 1638 smallpox had reached Boston, Massachusetts, in 1721 an outbreak caused the city to be abandoned, the fleeing residents spread the disease throughout the thirteen colonies. Smallpox would go on to cause six separate outbreaks in the United States through 1968.
The smallpox vaccine was developed in 1798 by Edward Jenner. By 1979 the disease had been completely eradicated, with no new outbreaks. The WHO stopped providing vaccinations and by 1986, vaccination was no longer necessary to anyone in the world except in the event of future outbreak. Currently the smallpox virus exists only in laboratories (25).
Leprosy, also known as Hansen’s Disease, is caused by a bacillus, Mycobacterium leprae. It is a chronic disease with an incubation period of up to five years. Symptoms often include irritation or erosion of the skin, and affects on the peripheral nerves, mucosa of the upper respiratory tract and eyes. The most common sign of leprosy are pale reddish spots on the skin that lack sensation.
Leprosy probably originated in India, more than four thousand years ago. It was prevalent in ancient societies in China, Egypt and India, and was distributed throughout the world by various groups, including Roman Legionnaires, Crusaders, Spanish conquistadors, Asian seafarers, European colonists, and Arab, African, and American slave traders. Some historians believe that Alexander the Great's troops brought leprosy from India to Europe during the 3rd century BC. With the help of the crusaders and other travelers, leprosy reached epidemic proportions by the 13th century.
Once detected, leprosy can be cured using multi-drug therapy (MDT), composed of two or three antibiotics, depending on the type of leprosy. In 1991 the World Health Assembly began an attempt to eliminate leprosy. By 2005 116 of 122 countries were reported to be leprosy free.
On Nov. 6, 1880 Alphonse Laveran discovered that malaria (then called "Marsh Fever") was a protozoan parasite, and that mosquitoes carry and transmit malaria. Malaria is a protozoan infectious disease that is generally transmitted to humans by mosquitoes between dusk and dawn. The European variety, known as "vivax" after the Plasmodium vivax parasite, causes a relatively mild, yet chronically aggravating disease. The west African variety called caused by the sporozoan parasite, Plasmodium falciparum and results in a severely debilitating and deadly disease.
In 1492, Malaria was a disease endemic to Europe and Western Africa. Plasmodium falciparum became a real threat to colonialists and indigenous people alike when it was introduced into the Americas along with the slave trade. Currently parts of the third world are more affected by Malaria than the rest of the world, and many inhabitants of sub-Saharan Africa are affected by recurring attacks of malaria throughout their lives. In many areas of Africa there is limited running water and instead wells and cisterns are used, there are plenty of sites for breeding and spread of the disease. This is not a surprise since mosquitoes use areas of standing water like marshes, wetlands, and water drums to breed.
The bacterium that causes tuberculosis, Mycobacterium tuberculosis, is generally spread when an infected person coughs and another person inhales the bacteria. Once inhaled TB frequently grows in the lungs, but can spread to any part of the body. Although it is very easy to spread TB, in most cases the human body is able to fend off the bacteria. However, TB can remain dormant in the body for years, and become active unexpectedly. If and when the disease does become active in the body, it can multiply rapidly, causing the person to develop many symptoms including cough (sometimes with blood), night sweats, fever, chest pains, loss of appetite and loss of weight. This disease can occur in both adults and children and is especially common among those with weak or undeveloped immune systems.
Tuberculosis (TB) has been one of history’s greatest killers, taking the lives of over 3 million people annually and is often called the white plague. According to the WHO approximately fifty percent of people infected with TB live in Asia. It is also the most prevalent, life threatening infections among AIDS patients and has increased in areas where HIV seroprevalence is high.
Air travel and the other methods of travel which have made global interaction easier, have helped increase the spread of TB across different societies. Luckily, the BCG vaccine was developed, which prevents TB meningitis and miliary TB in childhood, however the vaccine does not provide substantial protection against the more virulent forms of TB found among adults. Most forms of TB can be treated with antibiotics to kill the bacteria. The two antibiotics most commonly used are rifampicin and isoniazid.
AIDS/HIV is among the newest and deadliest diseases. According to the World Health Organization it is currently unknown where the HIV virus originated, and is believed that it may have been isolated within many groups throughout the world. It is believed that HIV arose from another, less harmful virus, that mutated and became more virulent. The first two AIDS/HIV cases were detected in 1981, and as of 2004, an estimated 1,039,000 to 1,185,000 persons in the United States were living with HIV/AIDS, and an estimated 39.5 million people worldwide are living with HIV”. The WHO also reports that there has been a 50% increase in HIV infected people since 2004 and despite global efforts, awareness and prevention programs don’t seem to be reducing the numbers of new HIV cases in many parts of the world. The biggest problem with prevention programs is that they are difficult to maintain and, as a result, the protective measures usually do not last long after the program stops.