Diseased Vs. Infected: Why the Difference Matters

( Canva )

We live in a mire of bacteria and viruses. Every day, we are exposed to pathogens and microbes that could make us sick. Fortunately, our immune systems can typically handle that, said Jim Lowe, DVM, director of the College of Veterinary Medicine I-Learning Center at the University of Illinois. 

So, what makes COVID-19 different? 

Not only is it a new strain of coronavirus that we do not have immunity for, but there also is no vaccine. In order to best understand the challenges of COVID-19, Lowe explained during a farmdocDAILY webinar, you have to begin by differentiating between infected and diseased. 

Diseased means you have been exposed to a pathogen that causes you to have a response and feel sick. Infected means you have been exposed to a pathogen and although you may not have a response and feel sick, you can still shed the virus and pass it on to others. 

“It’s a bit hard to understand,” Lowe said. “When we’re talking about measuring cases, only the most severe and diseased are counted because they needed to go to the hospital, or somebody thought they needed to be tested.”

Unfortunately, this does not account for the number of infections, he explained. The number of infections are really important, however, because someone who's infected and shedding the virus can infect another person. 

He said that's one of the big differences between this coronavirus and the first SARS outbreak that happened in China several years ago. That virus strain was much more severe but didn't transmit very well between hosts. People who were infected were also diseased, making it easy to tell who was infected.

“It is very apparent with this virus that we have a lot of infected people who are not diseased, and those infected people can cause someone else to become infected without knowing it,” Lowe said. 

This is a common occurrence with many diseases of livestock. Lowe said that’s a critical difference in this disease compared to other diseases and why the transmission of this virus has been so crazy.

Initial efforts to screen for temperature may have helped some, but that measure could not tell who was infected. Infected people were shedding the virus, but not showing signs of fever or disease. 

“At the end of the day, we never have enough test kits to test enough people, or enough animals, to really know where the infection is at,” he said. 

To really control this disease, he said our only choice is to stop contact and stop movement of the virus.

3 Strategies to Control Infectious Disease
Lowe said there are three buckets to choose from when it comes to controlling infectious disease. 

“Every critter, human or [animal], fits into one of three buckets. You're either infected with the disease, resistant to infection or susceptible to infection. And when we have a novel pathogen, everybody's susceptible,” Lowe said. 

Control focuses on blocking the infected and susceptible groups from contacting each other. That serves as the basis of current control strategies. 

Lowe believes the country is quickly moving to the place where an antibody test would allow people to know who was recovered, so they could move to the resistant bucket and possibly go back out in the workforce. 

3 Ways to Disrupt Transmission
To help prevent infectious disease transmission, there are three main methods: hygiene, cleaning and disinfection; exclusion; and segregation.

Hygiene is by far the easiest method to implement, but it is exceptionally hard to get done, Lowe said. Looking at human healthcare studies, there is about 50% efficacy in a hospital when it comes to handwashing. 

“If human healthcare workers who are educated and understand the risk only get it done 50% of the time, I don't want to think about how effective we are washing our hands every day,” Lowe said.

The other methods, exclusion and segregation, are applied in animal agriculture all the time, he added. 

Exclusion means keeping risk out, which is what is happening in nursing homes and with high-risk people. How do I just keep everything out of that nursing home so I don’t put it at risk?

Segregation is what our country is trying to do, he said. 

“Let’s keep everybody apart and not let them mix and not use those things routinely. Segregation is this idea of shelter-at-home. We're not excluding everything; we're saying let's do life in a way that's less likely to have contact between infecteds and susceptibles.”

More from Farm Journal's PORK:

Here's What Makes Coronavirus and African Swine Fever Different

PRRS: Deciphering the Mystery Disease

Glitter Snot and Virus Swapping: Hands-on Biosecurity Practice

Autogenous Streptococcus Suis Vaccine Protects Piglets