Be afraid. Be very afraid.

While the U.S. public-health system has made major strides in stopping smoking and preventing HIV/AIDS, there is still a slew of infectious diseases, new and old, that all Americans need to start thinking about.

Centers for Disease Control director Thomas Frieden outlined the looming crises in a talk this week, focusing on awareness and prevention while still name dropping a lot of scary stuff: the plague, bird flu, and killer measles. It was not a day for germophobes.

Never heard of H7N9 flu? Well, you might soon. It’s a recently discovered form of bird flu that Frieden said “is acting quite a bit like SARS,” the viral respiratory infection that has killed more than 8,000 people and created a worldwide panic in 2003.

H7N9 is lethal and spreads faster than any other identified strain of bird flu. It moves from animals to humans, but, unlike previous versions of bird flu, doesn’t make animals sick. As a result, infected flocks can’t be contained, and there’s no effective vaccine.

This strain was discovered in China this past April. Of the 130 human infections reported, there were 44 deaths related to respiratory illnesses. Most of the infections were found in people with direct exposure to poultry.

Infections in China have tapered off, but this bird flu appears to be as seasonal as human flus, and may come back stronger as it gets colder.

“The only thing protecting us from a global pandemic right now is the fact that it doesn’t yet spread from person to person,” Frieden told the National Press Club on Tuesday. Gulp.

He’s also concerned about antibiotic-resistant tuberculosis, which he said is “spreading in long-term-care facilities and hospitals widely.” Then there are what the CDC calls “intentional diseases”—chemicals or diseases like anthrax, which could be used as biological weapons.

What’s highest on Frieden’s agenda? The plague.

After a person in rural Uganda was infected with the plague by a sick rat or flea this year, 130 people were given preventive medication by CDC workers. That infection was contained.

But this scourge of the Middle Ages could have a terrifying modern application, too: “Plague is one of the organisms that we’re concerned about in terms of its potentially being used as a bio weapon,” Frieden said.

Another illness you might want to start taking seriously: the measles.

There are still over 400 deaths a day from measles around the planet, Frieden said, with plenty of infections in the U.S. from a malady he called “perhaps the most infectious of all the infectious diseases.”

“If you take, oh, let’s say a room with a couple hundred people in it, and there is one person coughing with measles and there are just three or four others who are susceptible, they’ll probably get it. It’s that infectious,” he said.

It wasn’t all bad news from Frieden.

The most preventable cause of death—smoking—has plummeted among Americans in recent years. Frieden pointed to CDC data that show more than 1 million Americans have tried to quit smoking, and 100,000 or more have quit smoking altogether. And, crediting the President’s Emergency Plan for AIDS Relief, Frieden said some 5.5 million more people are able to live full lives even if they are HIV-positive.

Still—what about H7N9, drug-resistant TB, measles … and the plague?

Knowing about potential threats and focusing on prevention are key, Frieden said.

“I don’t think it’s rocket science,” he says. “Figure out what the problems are. Figure out what the solutions are. Implement those solutions. See if they’re working … tweak them, fix them, adjust them if they’re not.”

Fingers crossed.

Correction: The original version of this article incorrectly identified H7N9 flu as MERS coronavirus.