So what can people do to prevent the spread?
Dr. Shaffner said that, with West Nile, "Try to avoid mosquito bites. Use repellent, long sleeves, long trousers. Look for standing water around your house and get rid of it, including in your gutters.
"With Hanta, if you go out, don't let mice eat your food. Keep it away from the mice. You don't want to attract the bears or the mice."
And for Lyme disease - which are transmitted by tick bites - Dr. Shaffner said, "You also always want to inspect yourself, and have somebody look on the back of your head and back of your back to see if you've had a tick bite. Fortunately tick bites are common but Lyme disease is very uncommon, relatively speaking."
Gayle King asked about a recent report of a case of Bubonic plague - a little girl whose parents first thought she had the flu.
"She saw a dead squirrel, I think covered the squirrel...she wanted to bury it with the T-shirt," said Dr. Shaffner. "Some of the fleas got on the T-shirt and then bit her."
He said flu is often the initial illness: "You get a flu-like illness, you're feeling poorly, you've had fever and it looks like just some sort of common infection. What you need is an astute doctor and a history of the exposure."
"There was a great fear of Asian flu and then it was not as severe as we expected," Rose said. "What's been the consequence of that?"
"We have periodic episodes of influenza with new influenza strains," said Dr. Shaffner. "They usually come from Asia. The last one came from Mexico. Those viruses, they don't need passports, so we live in one world and so we need strong public health in order to be able to respond to these infectious threats which are always around us.
"I know it's the 21st century, but those infections are still with us."
To watch a video of Dr. Shaffner's interview click on the player above.