Viruses 101: A Deep Dive Into These Dangerous Infection Agents

A closer look at the weird, dangerous infection agents.


Been thinking about viruses a bit lately? Yeah, we are, too.

The recently discovered coronavirus is one of a large family of viruses that cause illnesses ranging from the common cold to more severe diseases, such as severe acute respiratory syndrome (SARS) and the current one we’re so worried about, COVID-19. 

So we asked Scott Terhune, associate professor of microbiology and immunology at the Medical College of Wisconsin, for some insight into viruses, in general, and how and why they make us sick.

What is a virus? 

Viruses are relatively simplistic entities but have great potential to cause significant disease. Viruses usually cause disease because when they replicate, they cause damage. Take influenza, for example. It gets into the cells in the lungs and it will replicate. The virus is killing cells in order to do that. Then the immune system tries to shut that down. It’s that combination of our immune system targeting our cells and the virus killing those cells that ultimately causes a disease.

What’s the difference between a virus and other types of germs?

The other type of germ that we commonly talk about is bacteria. Bacteria are living cells. They have all they need to grow and divide. Viruses, on the other hand, outside of a living entity, are inert. They aren’t going to survive outside of a host cell. When we are talking about this social separation, the goal is to not allow a virus to enter another person, where it will find a living cell to replicate. Bacteria, on the other hand, are self-sufficient. Antibiotics can prevent the bacteria from growing and dividing but don’t work with viruses. That’s where vaccines come into play, where you take a piece of that virus and introduce it into our bodies. That’s essentially a means of training our immune system.

Why are viruses so difficult to eliminate? 

To eliminate a virus, you have to eliminate its reservoir. That can be very difficult to do. Influenza actually has non-human reservoirs: pigs. That virus can then be transmitted back to humans. That makes it very difficult to control or eliminate. Until those reservoirs are eliminated, the virus has the potential to continue to spread. Viruses also adapt to their hosts. The big challenge with this coronavirus is that it went from one species into humans. It’s adapted to humans, and when our immune systems aren’t prepared, it often becomes highly pathogenic.

What are the best ways to keep from contracting or spreading a virus? 

A virus gets into our bodies through access points like our mouths, noses and eyes. Therefore, you wash your hands. You don’t touch your face. You cough into a tissue. Common-sense things and breaking habits. 

This story is part of Milwaukee Magazine‘s May issue. 

Find it on newsstands or buy a copy at

Be the first to get every new issue. Subscribe.



Rich Rovito is a freelance writer for Milwaukee Magazine.