By: Jillian Carmichael, 4th year student in the Biomedical Sciences Graduate Program

“Did you see that post? It’s going viral!”

Social media can be a strange beast. Within hours, funny videos about pandas going down slides or kids saying the most ridiculous things are all over the Internet. These viral posts saturate social media and it’s almost impossible to avoid seeing them (or at least hearing about them).

It’s curious how someone can go from complete Internet obscurity to “famous” within hours of posting content on social media. Considering the billions of social media posts made each day, how do certain posts rocket to viral status while most remain unremarkable? It takes the perfect combination of good timing, interesting content, the right audience, and plain old luck for a post to go viral.

Implicit in the terminology “going viral” is the concept of infectivity. In order for a social media post to reach viral status, it must spread quickly and extensively. In fact, a social media post going viral is very similar to how an actual virus can cause an epidemic.

In the same way a social media post requires the perfect conditions to go viral, biological viruses also have stringent requirements to spread efficiently. Luckily, the vast majority of existing viruses are not capable of causing the widespread disease outbreaks, like those popularized in Hollywood movies such as “Contagion.” Most viruses either cause minor illnesses (such the common cold) or more severe disease that is limited to small populations. But every now and then a perfect storm arises and a viral infection triggers widespread death and destruction.

What are the elements that allow these select viruses to, in pop culture terminology, “go viral?”

In order to understand what viruses are and how they spread, a little terminology is required. Simple stated, a virus is a microscopic infectious agent composed of proteins, genetic material (think DNA or RNA), and (sometimes) a lipid envelope. The type of organism a virus infects is the called the host—viral hosts can range from bacteria to honeybees to humans. Finally, viruses utilize a process called replication to make more of themselves (“replication” is the viral version of “reproduction”).

A major limiting factor true for all viruses is their parasitic nature—viruses completely rely on their hosts to replicate. To make more viral particles, a virus must enter a host cell and hijack the cellular machinery to produce its progeny. However, viruses need the right signal to enter the right cell. This first level of viral selectivity concerns cellular tropism (which type of cell the virus can infect). Since there are many different cell types, it is not surprising that different viruses prefer to infect different cells. Moreover, some viruses have broad tropisms and can infect many different types of cells. This ability gives these viruses a distinct advantage—the more cell types a virus can infect, the better its ability to spread within a host and between hosts.

Regarding social media, this is like comparing a post that can only be shared via Facebook with a post that can be shared by a multitude of social media platforms. The post that is compatible with a variety of social media websites—like a virus than can infect many different cell types—has a higher likelihood of going viral.

As a general rule, human viruses infect humans while animal viruses tend to stay within their respective species. Occasionally a virus will jump to new species in what is termed a zoonotic infection (think Ebola spreading to humans from infected bats). Oftentimes, zoonotic infections can result in more severe disease than human viruses, since these viruses are not adapted to the human immune system. The ability of a virus to jump from one species to another requires close personal contact and exposure.

In the same way, viral media posts are often shared directly between friends and family. Instead of seeing the latest viral video on Twitter or YouTube, your mom or dad could show you the video directly during a family dinner. Not only does this type of social media exposure require personal contact, it can also jump between different generations of people. (It’s not quite the same as jumping between species, but the comparison is close enough).

Pathogenicity is another element by which viruses are characterized. Simply stated, pathogenicity refers to a virus’s ability to cause disease. A highly pathogenic virus is one that can cause severe damage or death to its host, like Smallpox or Ebola. Fortunately, most human viruses are not highly pathogenic, and therefore the majority of human viral infections do not cause widespread death and destruction.

Pathogenicity can be compared to the content of social media posts. While the content of viral social media posts may seem mundane, there is something special about them that captivates and compels an audience to consume, propelling the post into the viral stratosphere. Social media posts may be humorous, heart wrenching, or incendiary, but ultimately there is something special about the content that allows these posts to go viral. Highly pathogenic viruses also contain special contents that program the virus to be extremely destructive and deadly.

Finally, viruses can be characterized by their transmissibility. Transmissibility—how a virus is passed from one infected host to an uninfected host—varies between different viruses. Some viruses can only be spread to a new person via direct contact with infected bodily fluids. Viruses that use this type of transmission, such as HIV, can cause severe disease in infected people, but actually getting a new host infected is difficult. HIV is a serious human pathogen, but because it’s not easily transmitted between hosts, is unlikely to cause a worldwide pandemic with billions of people affected.

Viruses that are easily transmitted from one host to another pose the highest threat for developing into a pandemic. Typically, viruses that can spread through respiratory droplets (like a sneeze or a cough) display high transmissibility. Viruses such as Influenza or SARS can spread very quickly throughout a population because transmission can happen in the air. High transmissibility can be compared to how likely a social media post is to be shared and re-shared. The more likely a post to be re-posted by a wide variety of people, the more likely the post will go viral.

Thankfully, unlike the continuous viral postings in social media, most viruses do not have all the required characteristics to “go viral” and cause a pandemic. In fact, widespread deadly pandemics are a relatively rare event in human history, although they definitely do happen.

By better understanding how viruses can gain the right tropism and infect humans, be highly pathogenic, and gain high transmissibility, scientists can better prepare for and predict which unknown pathogen may cause the next outbreak.

—

Jillian Carmichael is a 4th year PhD candidate in the Biomedical Sciences Graduate Program. She works in Dr. John Wills’ lab studying the molecular mechanisms of Herpes Simplex Virus Type 1 spread.

Jillian also enjoys running, reading, hiking, and going on adventures with her daughter and husband.