AMNA NAWAZ: It's summertime, and ticks are out in full force.

While, in certain parts of the country, ticks have long been an issue.

They're now spreading to new regions and bringing new threats.

William Brangham has the latest.

WILLIAM BRANGHAM: For many years, ticks have been viewed as a menace because they sicken us with Lyme disease.

About half-a-million Americans get Lyme every year, and it can cause serious, sometimes lifelong health problems.

But now ticks are infecting us with some different ailments, including one called Alpha-gal syndrome, which can give humans a dangerous allergy to red meat and to dairy products.

For the latest on these tiny blood-sucking terrors, we turn to Holly Gaff.

She's a mathematical ecologist who studies ticks at Old Dominion University.

Holly, thank you so much for being here.

The CDC says that, so far this year, E.R.

visits for tick bites are way above normal, almost going back -- they haven't seen it this bad since, I think, a decade ago.

Do you have a sense as to why we are seeing such a busy start to tick season?

HOLLY GAFF, Old Dominion University: That's a great question.

I think tick populations are extremely complex in understanding where they are.

This has certainly been a big tick year starting off.

I'm really curious to see how it's going to go through the rest of the season, whether we have just jammed them all in the first part of it.

But they are up.

They are up in a lot of places.

I think there's a couple complicating factors of the combination of a very cold winter, which is kind of contradictory to what people would think.

They think cold should kill a tick.

But, honestly, the cold probably killed some of the things that they would have fed on, instead of you and me.

So they're kind of -- I jokingly call them hangry ticks at this point that are up and they haven't found food until they find us.

WILLIAM BRANGHAM: Great.

That's just - - way to give us some summer terrors, as an army of hangry ticks out there.

HOLLY GAFF: Exactly.

WILLIAM BRANGHAM: Are there more regions of the country, different regions of the country that are more vulnerable to this explosion of ticks?

HOLLY GAFF: Yes, so I think the best way to understand the explosion of ticks as well is also, these particular ticks, these lone star ticks, ticks really like to feed on white-tailed deer.

And so as white-tailed deer populations continue to explode, the ticks that come with them do.

We have also built and moved into the exurbs and the suburbs and the areas.

We like a little bit of forest around us, and so we have moved to them and we have created the buffet for these little - - as I described them, hangry little ticks.

WILLIAM BRANGHAM: So Lyme disease has been the principal problem as far as human health.

Is that still the principal concern?

HOLLY GAFF: It's a mixed bag.

I mean, Lyme disease is nothing to be trivialized at all in all of this.

I think it's just the recognition of this newer ailment of Alpha-gal syndrome that is coming along.

Lyme disease has been moving south, but it's definitely been more in the Midwest and Northeast.

And so it -- but Alpha-gal and lone stars are moving north.

So it's -- everything is moving every direction.

And I think there's a whole bunch of other tick-borne diseases that also can -- are smaller numbers of cases, but certainly of concern for those who are in fact impacted by that.

WILLIAM BRANGHAM: So, specifically about that Alpha-gal syndrome that you're talking about, that is something you get from a tick that causes an allergy to meat and dairy products, to red meat?

Is that correct?

HOLLY GAFF: Yes, that is correct.

So the saliva of a lone star tick in particular and some other tick species around the world have a sugar will basically expose you to the Alpha-gal protein -- pardon me -- carbohydrate.

And so it's a delayed allergy.

It's a very bizarre series of steps in the immunology of the human and all non-Old World primates actually that can have the Alpha-gal allergy that can be triggered from this exposure.

And, again, it depends on your genetics.

So not everybody's going to have this immediately after being bitten by a lone star, but certainly a lot of folks have.

WILLIAM BRANGHAM: I see.

So for people who are hearing about this, might be not familiar with how to protect themselves, what are some basic guidelines of how to keep ticks off you?

HOLLY GAFF: I think the best bet is to be aware, that you are looking and you are trying to find them before they find you.

So stay -- if you go outside in areas that will be infected with ticks, and that'd be anywhere that you see a white-tailed deer, that's a great indicator that ticks will be nearby.

You definitely want to stay on trails if you're hiking.

Or, in your own backyard, be aware when you're going near wooded areas, where there will be more ticks, and so being aware to where to look on your body, check yourself, check your children, check your pets.

If you do want to use chemicals, there are some things like DEET that will deter them some.

I always recommend permethrin as well if you are willing to use that on your shoes at least.

That can kill the tick as it comes across that.

But it's just -- you can't -- nothing will beat checking yourself for ticks consistently while you're outside, as well as when you get back inside.

WILLIAM BRANGHAM: I mean, I know you're not a doctor, but I know, given your exposure and your expertise, you must have done this a million times.

But if one gets through those defenses and is stuck in you, there seems to be so much misinformation out there about how to get them off.

I have read petroleum jelly, burning them with matches, nail polish remover.

What is the best way safely to get a tick out of you?

HOLLY GAFF: The best recommendation, CDC recommendation, World Health Organization recommendation, is to get a pair of tweezers if possible and pull the ticks straight out.

Just -- it does not want to be irritated out of there.

I mean, all the other techniques that you're talking about will probably do more harm to you.

But if get a pair of tweezers, put it flat against your skin and pull straight up, don't twist, don't crush the tick.

And your whole goal is just to get as much of the tick out as possible.

First I would say also wash the area.Don't panic.

It is disconcerting to find one.

But the sooner you get it out, the better, because the longer you wait to do anything else, the more exposure you are to both the saliva from Alpha-gal, as well as all the pathogens it could be transmitting.

WILLIAM BRANGHAM: All right, that is Holly Gaff of Old Dominion University.

Thank you so much for your expertise.

HOLLY GAFF: Thank you.