The Black Death Pandemic Along The Silk Road – Epidemics
Links to Online Sources:
https://www.history.com/news/silk-road-black-death
https://covid.cornell.edu/travel/
The Silk Road is the most renowned trade route in the world, connecting numerous countries from East Asia to Europe. While it empowers communities to trade products and share their knowledge, culture, beliefs, and innovations, it also allows diseases to spread across countries. In this case, the Black Death plague severely influenced people along the route from Asia to Europe, killing more than 50 million people in less than 10 years. The article explains that the Silk Road serves as a crucial contact network for the Black Death infection, and its content is significantly related to our class discussion regarding epidemics. While its name seems like a single route, Silk Road is composed of multiple paths linked to numerous villages and towns, with traders frequently traveling between them. As illustrated by the graph below that shows a proportion of the Silk Road, there are many nodes and they are all connected to one or more of the other nodes.
The transmission of the contagions among countries along the Silk Road can be manifested using the branching process. While the Black Death is said to originate in Central or East Asia, the exact city remains unconfirmed. In the illustration below, I would like to use Tashkent as the starting node where the first infected person appears.
When traders travel from East to West, they go from Fergana to Tashkent, and infected travelers thereby infect people in Tashkent. Traders not only travel through nodes along the route but also trade at and between nodes. Therefore, when a patient from Tashkent trades with someone from Nukus, Khiva, Bukhara, or Samarkand, the traders from these locations are exposed to the microbes. If these traders also get infected, they are capable of infecting people at more nodes when they trade. For instance, after the disease transmits from Tashkent to Bukhara and Samarkand, Shahrisabz is also at risk, since people there also trade with people in Bukhara and Samarkand. The transmission between nodes is very likely to happen because of many factors. Similar to all other epidemics, the spread of the Black Death is based on the production number p times k. On the one hand, as the plague happened in the 1300s, people do not possess the knowledge and technology to effectively decrease the probability of infection. Trades also occur in close physical proximity, which makes the transmission of microbes from a person to another extremely likely. As a result, the value of p is not controlled. On the other hand, there is more than one trader at a node, so there are multiple trade exchanges between each pair of nodes, making the value of k very high. Furthermore, as discussed earlier, nodes are interconnected and one node could link to more than one other node. Here, even if the disease does not spread from Tashkent to Khiva, Khiva is still at risk as long as the disease arrives in Nukus, as Nukus is also connected to Khiva. The interconnectivity of the network makes various locations even more exposed and vulnerable to potential infection.
Because p and k are high, it is very likely that the basic reproduction number is significantly greater than 1, so the plague persists and becomes more and more severe, reaching more and more locations. After the disease gets into a new location through a trader, all citizens are exposed to the risk of getting infected. Such a process is also comprehensible with the branch model.
Apart from p still being ineffectively managed, there are meanwhile several types of connections making k also remain high. After traders bring back products, they either sell the products by themselves or sell them to the vendors. They thus come in contact with citizens from all kinds of places in addition to their personal network. After the first wave, those who get infected with probability p initiate the second wave. The vendors interact with more customers, who then spread the disease among friends and families. More and more waves occur as, within each village and town close to the Silk Road route, each individual node is connected to many other nodes within that location. Consequently, after the Black Death successfully gets into all locations along the route through trades, millions of people then get infected through subsequent waves, eventually resulting in more than 50 million deaths.
What makes the pandemic even more devastating is the nature of the Silk Road – it is a two-way route. As traders travel from East to West, traders also travel back from West to East. As suggested by the article, the Black Death spreads East to West and then back again. This is related to the concept of a SIR model. After the plague initiates in Central or East Asia and starts to spread to the West, some people are left uninfected and Susceptible at the origins, and some people might recover from the disease and become Removed. If traders who have left the East do not travel back, those Susceptible and Removed citizens are free from the Black Death. However, when traders bring the plague back to the origins in the East again from the West, those who are Susceptible and Removed are again at risk. On the one hand, even assuming that there are no more Infected people at the origins, Susceptible people are now again in contact with Infected traders back from the West. On the other hand, the immunity for the Black Death might be temporary, meaning that these Removed individuals who have just recovered from the disease are again Susceptible. Consequently, while the Black Death devastates people in the West, it meanwhile also devastates people in the East.
I find this phenomenon regarding the Silk Road and Black Death very relevant to Cornell’s schedule and travel policies specific to the COVID-19 pandemic. As we all know, in order to minimize unnecessary traveling. not only was the fall break canceled this semester, but the instruction also became entirely online after the Thanksgiving break. After students returned to their homes for the Thanksgiving break, they resumed the classes online instead of traveling back to Ithaca. These practices designed by Cornell are very reasonable and effective for alleviating the pandemic. Students’ routes back home are very similar to the routes of the Silk Road.
Just like the Silk Road traveling from East Asia to Europe through many locations, students must pass several locations when they travel from Cornell to their home. For example, a student might need to take a flight at Syracuse Airport in order to fly back home. Therefore, the student must travel from Ithaca to Syracuse first before going home. At the same time, other passengers at the airport are from various other cities. This significantly increases the number of contacts k and thus increases the likelihood of getting infected, and this is just one student’s route. When thousands of students all travel back home at the same time, their routes outnumber the routes on the Silk Road by far. When the students arrive at their homes, they also interacted with their families and friends, just like how the traders do when they go back to their hometown after trading. If Cornell decided to continue in-person instruction after the Thanksgiving break, all students needed to travel through the same routes again, doubling the number of contacts and the risk of infection, similar to the concept of the Black Death spreading from East to West and spreading back again. By removing this other round of traveling with the transition to online instruction, Cornell effectively minimizes the chance of a COVID-19 outbreak, thereby protecting students from further infection. Meanwhile, students should also try their best to travel with the most direct route from Cornell to their home, as doing so can help them minimize interactions with people from other locations, which are similar to the villages and towns along the Silk Road. By doing so, students also protect their personal network at their homes from the microbes that they might have caught from other travelers.
By implementing effective policies to reduce k as well as prevention methods like wearing masks and washing hands that reduce p, Cornell has successfully prevented any unnecessary outbreak. Scientific research and knowledge on networks have substantially empowered people to keep epidemics under control in contemporary society, thus preventing devastating impacts of the Black Death along the Silk Road from happening again.