In this video, Dr. Offit introduces the different types of viral infections and how some viruses remain in our systems after first contact. To find out more, read the accompanying article in the January 2019 issue of the Parents PACK newsletter.
Paul Offit, MD: Hi, my name is Paul Offit. I’m talking to you today from the Vaccine Education Center here at the Children’s Hospital of Philadelphia.
And I thought we’d spend a few minutes talking about viruses. Sort of how they work. How they infect the person. How the person responds to them.
And I think you can divide viruses up into three different categories. The first are the viruses that cause symptoms at the site where they first enter. So, for example, influenza virus is a virus that enters through the nose and throat. It then reproduces itself in the cells that line the nose and throat and causes symptoms, and so the incubation period, meaning the time from when one is first exposed to the virus to when one develops symptoms of the virus is very short. So, for influenza, it can be as short as 18 hours.
Rotavirus is another example. There’s a virus that enters through the mouth and the stomach, and then the intestine. It reproduces itself in the cells that line the intestine. It causes fever and vomiting and diarrhea. But again, incubation periods are short because it’s causing an infection right where it enters. In the case of rotavirus, it can be as short as one or two days.
Then there’s sort of this second group of viruses. These viruses, like measles or mumps or German measles/rubella. They enter usually through the nose and throat, and then they reproduce themselves locally. But then they spread into the bloodstream. The virus enters the bloodstream, and then it travels to sites distance to where it initially entered. So, for measles for example, it will travel to the lung, or it will travel to the skin, or it will travel to the brain, or it will travel to the liver. That takes time.
So now, because virus in the bloodstream is an important part of how the virus causes disease, incubation periods are longer. So, instead of being one to two days, which is true for a virus like influenza or rotavirus. It’s more like 8, 10, 12, sometimes 14 days, sometimes as long as 21 days, because it takes time for all of that to happen.
The third group of viruses are viruses that actually can live for a long time in your body. So, a virus like herpes simplex virus, which again usually enters through the nose or throat or enters through the genital tract, initially infects, but then it can travel up for example into the nerves and cause longer-lived disease.
So, for example, the chickenpox virus, which is a type of herpes virus actually; it’s in the family of herpes viruses, usually, like measles virus, it initially enters through the throat. It then travels through a variety of areas through the blood, areas like the skin and lungs, and it causes disease, but then what it does is, it actually lives silently in the nervous system so it can reawaken months, or years or decades later in the form of shingles.
Human papillomavirus, or HPV virus, also can infect one and then you appear to recover, but what you don’t realize is that the virus has eventually transformed a cell. So, after it infects it, it transforms it to become a cancerous cell, which may be not be apparent for 15, 20 or 25 years later.
Same thing with hepatitis B virus. That virus too can infect the liver for a long period of time, and then cause cancer decades after you’re first infected.
So, viruses have different strategies for how they induce disease, largely based on where they enter, and where they travel after they enter, and then what happens to them after they’ve already caused an infection.
So, thank you for your attention.
Related Centers and Programs: Vaccine Education Center