Faster transportation makes it easier for epidemics to spread. On the other hand, modern science has learned how to contain many of them. Do diseases spread differently today?

Epidemics have annihilated whole populations in the past. Today, it seems that even if we haven’t eliminated them completely, at least we’ve managed to curb the most severe infectious diseases. But that’s just an illusion, which is the case mostly in developed countries, especially those in Europe and North America. In developing nations, however, there are still epidemics that kill millions of people every year. Has something changed over the years in how diseases spread?

A deadly past

One of the first documented plagues was in ancient Greece in the fifth century BC. It was probably a typhus pandemic, and, according to some estimates, 100,000 people died. During the days of emperor Marcus Aurelius in the second century AD, a smallpox epidemic raged throughout the Roman Empire, killing an estimated 2,000 people per day and wiping out a quarter of the empire’s population overall. And the history books document many other mass epidemics.

The most famous pandemic was the Black Death, a devastating plague in Europe, which peaked between 1347-1351 and showed just how diseases can spread quickly between countries and continents: The pandemic broke out in China and was carried with merchants along the Silk Road to the Crimea peninsula. There, the Mongols used it as they laid siege to the city of Caffa. They threw bodies of soldiers that perished from the disease over the city’s walls, to infect its residents; probably, the first known instance of biological warfare. From Crimea, the disease spread to Constantinople and to the shores of the Mediterranean, travelling north from Italy, deep into the continent and spreading to the British Isles and even as far as Greenland. The loss of human life was astounding: 35 million deaths in China and similar numbers in Europe, where the estimate is that half of the population died.

 

המוות השחור בטורנאי, בלגיה 1349

The Black Death in Tournai, Belgium 1349

In the 20th century, we witnessed two major pandemics – one was the Spanish Flu, which broke out in 1918 and killed an estimated 75 million people, and the other was AIDS, which began to spread in the west at the end of the 1960s and continues to rage today in sub-Saharan Africa. It has killed about 30 million people up till now. In comparison to those, the flu pandemic that spread from Hong Kong in 1968 killed “only” one million people around the world within two years.

Since the beginning of the 21st century, we’ve witnessed many small outbreaks that made big headlines – the SARS virus in Asia, the swine flu , avian flu, the local breakout in Israel of polio, and more recently, the Zika virus breakout, which isn’t deadly but can cause paralysis and birth defects. Simultaneously, “routine” epidemics like malaria continue to surge in developing countries.

 

מחלקה לטיפול בחולי שפעת בבית חולים בארה"ב, בזמן מגיפת השפעת הספרדית

A ward for flu patients in an American hospital during the Spanish Flu

Trading diseases

One thing that stands out is that pandemics go hand-in-hand with globalization, and move from place to place on trade and tourism routes. That’s what happened when the Black Death travelled from China to Europe via the Silk Road, or during the conquests of the Americas, when European invaders imported numerous diseases, like smallpox and measles, to the new continents – with horrific consequences for the local populations. Some cases resulted from the contact between the conquered and the conquerors, and in order cases, it was intentional infection. The immune system of the natives didn’t know how to deal with unknown viruses and bacteria. The African slave trade also brought diseases, like Yellow Fever, to America.

Today, when transport between countries and continents is so simple, the spread of disease is even easier. A modern example is AIDS. The epicenter of the virus was probably in the Congo in the 1920s, and the expansion of railroads in the country in the 1960s spread the disease throughout the state. In 1967, it was exported to Haiti, and from there – it spread to the U.S. and to the rest of the world.

Today, the most concerning viruses for humans are those transferred by mosquitoes, especially in developing nations. Malaria, Yellow Fever, and Dengue Fever are very common, for example, in the equatorial countries, and kill millions of people. The combination of limited funds for research on diseases that don’t exist in wealthier countries, and the effective transmission, make it harder to curb these diseases.

 

יתוש מהמין Aedes aegypti, שמעביר את מחלות הזיקה, הקדחת הצהובה ועוד | Science Photo Library

An Aedes aegypti mosquito which spreads the Zika virus, Yellow Fever, and others. Science Photo Library

The Zika epidemic

A current example of such a disease, which also reached the southern United States and thus generated much research interest, is the Zika epidemic. The virus that causes it was first discovered in the Zika forest in Africa in the 1950s. In the 1970-1980s, it began to spread eastward and appeared in India, Indonesia, Malaysia, and Pakistan. In 2007, the first major outbreak of the virus occurred on the island of Yap in the Pacific Ocean, part of Micronesia. The outbreak apparently started when a tourist who carried the virus came to the island, as it isn’t probable that mosquitoes could fly so far.

In 2013-2014, there were additional outbreaks in other islands of the Pacific, especially in French Polynesia. In May 2015, there was another outbreak of the virus in Brazil, and subsequently, in Colombia, El Salvador, Mexico, Guatemala, Venezuela, and Paraguay. By December 2015, the U.S. reported the first outbreak in Puerto Rico and later on, in Texas and elsewhere.

Mosquitoes are an effective means of transportation for viruses and other diseases: They multiply quickly, move easily from one place to another, and are difficult to get rid of. A mosquito that carries a harmful virus can easily get stuck on an airplane or a boat travelling on a transcontinental route, or infect tourists, later returning home and bringing the disease with them. The bad news is that the expected climate changes in the 21st century may cause mosquitos that carry diseases like Zika and even Malaria to travel to areas distant from the equator, like the U.S. and Europe. In other words, what is perceived today as a problem in developing nations, could become a pandemic in developed ones.

Globalization is thus an effective disease-spreading tool, beginning with the early empires in ancient times. Furthermore, due to the notorious capability of some viruses, such as the flu, to mutate quickly, viruses have become highly dangerous – the flu in particular. The Swine Flu of 2009, for example, was actually a mix of genes from four different viral flu strains. Therefore, international flu pandemics “hitchhiking” aboard globalization are possible today, too.

Effective protection

The largest difference between the pandemics of earlier days and the modern era is the amount of research knowledge accumulating about the source of diseases, which enables humanity to develop the means to cope with them, including vaccines, antibiotics, and improvement of hygiene. The most impressive success was with the elimination of smallpox, which was one of the deadliest viruses in history. In the western world, diseases like tuberculosis, which caused many fatalities, were contained thanks to antibiotics and better sanitation, but they continue to be lethal in poorer countries.

In addition Globalization also has its benefits: The establishment of bodies such as the UN’s World Health Organization facilitates global efforts to supervise epidemic outbreaks and deal with them. Other organizations, like the Center for Disease Control in the U.S. addresses outbreaks on an international scale. These bodies did not exist in earlier centuries.

However, a grave new danger looms today, in the form of outbreaks of diseases from the use of biological warfare. Many countries keep viruses and other pathogens for military use, and accidents have already happened, causing leakage of the “weapons.” Such occurrences have inspired science fiction novels, like Stephen King’s The Stand. Moreover, the technology for creating viruses is more readily available than ever, and could reach hostile hands. One can only hope that countries – and the scientists themselves – will be responsible enough not to play with the epidemic fire.

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