Trigger warning.

- Trigger warning: This episode might make you feel a little itchy.

If it's spring or early summer, that means you've probably heard plenty about those little blood-suckers that love to treat humans like oversized Lunchables, and not in a way like Dracula, Edward Cullen, or Nosferatu will.

(spooky music) I'm talking about mosquitoes, ticks, and fleas!

I mean, just take a look closely, and I dare you not to scratch yourself.

Go on, I double dog dare you.

You can't, could you?

I'm scratching right now.

But you might not always be safe during those off-peak seasons when these critters are laying low for there's colder temperatures.

'Cause in fact, warmer temperatures are now being reported earlier and later in the year, and it gives time for ticks, mosquitoes, and fleas to have longer, more unpredictable feeding windows.

And with that widening window comes a whole mess of troublesome medical issues known as vector-borne diseases.

We're talking about the oldies and goldies here: dengue, West Nile, Zika, malaria, and Lyme disease.

Globally, according to the World Health Organization, there are more than 700,000 deaths attributed to vector-borne diseases each year.

Most of these affect parts of the world that experience warmer tropical temperatures and are spread by mosquitoes.

Here in the US, we have our hands full with ticks and fleas each year.

Reported cases of Lyme disease go up and up as well as some other interesting diseases, such as babesiosis, and alpha-gal syndrome, which causes an allergy to red meat, and even the plague.

So, vector-borne diseases are popping off like it's 1999, and there isn't really much we can do about it in terms of preventative medicine, because most of these diseases we're talking about don't actually have a vaccine or even a cure.

So what the heck is causing this uptick in the last few decades and what are scientists doing to keep up?

(dramatic music) (air whooshes) (lighthearted music) Look around.

We're at the Windy Hill Preserve right outside of Palo Alto in Northern California.

It's beautiful here, there's a lot of vegetation.

There are also a lot of vectors, like blacklegged ticks, which can transmit Lyme disease.

So hold up, what exactly is a vector, and what is a vector-borne disease?

- Vector-borne means anything that's transmitted by a vector, such as a flea, a tick, or a mosquito.

I will say there are different ways that arthropods can spread the diseases.

So you know, the classic model or what people think of is a mosquito or a tick that acquires a bacteria or a virus or a parasite by feeding on an infected host and then bites a human and transmits that pathogen or that infection to the humans.

There are other ways that vectors can transmit diseases to humans.

So for example, cat scratch disease, we believe humans are typically infected not directly by the bite of a flea, but actually the flea excretes the bacteria, it's called Bartonella henselae, in its feces, also known as flea dirt.

The cat scratches itself and gets that infection on its claws, and then as it scratches a human, it can introduce or infect that human, introduce the bacteria or infect the human that way.

- And just a fun PSA: While we're primarily focused on mosquitoes, fleas, and ticks, these aren't the only vectors to watch out for.

Black flies, aquatic snails, and lice are also crashing the party with the BYOVD, or bring your own vector disease, mentality.

For more information on these other vectors, check out the description below.

There are many vector-borne diseases out there, but for this episode, I wanna focus in on Lyme disease, which is the fastest growing vector-borne disease here in the United States, accounting for over 70% of vector-borne diseases.

- And so Lyme disease specifically is transmitted by the ixodes scapularis tick Also called the blacklegged tick.

On the west coast, in certain areas of Washington, Oregon and certain pockets of northern California, there’s the Ixodes pacificus so that’s also known as the Western backlegged tick.

We do see that it appears the range of these ticks is expanding, and there are likely many factors for that.

areas of Washington, Oregon and certain pockets of Northern California.

There's the Ixodes Pacific.

There have been changes in land use patterns, so back in the 1800s, there was a lot of farmland.

You know, these ticks like kind of the humid, shaded areas of forests and the borders between the forests and open areas.

So back in the 1800s, actually if you look at pictures of the Northeast, for example, there was a lot of kind of open swaths of farmland, so less forest actually than there is now.

As there have been fewer farms in those areas, there's actually reforestation, more forests, and that is a good habitat for ticks.

Climate change, we believe, is likely a factor with that as well.

We know that the ticks are expanding northward, and so with kind of warmer winters and other changes, that could potentially be a factor related to the change in the distribution of ticks.

I will say that we know that adult ticks, the adult black-legged ticks, in the winter, they can actually kind of wake up and quest and look for a blood meal and potentially bite humans.

They do that when the temperature reaches above 50 degrees.

So if you're having warmer winters and more days that are above 50 degrees, then you could potentially see more adult ticks out questing.

We do see seasonality with those reported cases.

You know, there are more cases starting in the spring into the summer, and then they kind of taper off in the fall.

At this point, we don't have enough specific data to say that the seasonality is extending.

We believe it is, but there will have to be more research related to that to really nail down.

- Let's take a closer look at the blacklegged tick, AKA the deer tick, AKA Ixodes scapularis, which is actually an arachnid, not an insect, but it is a proud card-carrying member of the Lyme Disease club as well as some other well-documented diseases.

From the day they hatch from eggs.

ticks need to complete a blood meal during every cycle of their life: from six-legged larva, to eight-legged nymph, throughout adulthood, and this process could take years to complete.

Now, during each blood meal, which is typically on a deer or a rodent, the tick may pick up the bacteria that causes Lyme disease, either Borrelia burgdorferi or Borrelia mayonii.

Once upon a time in the late 1990s, there was an FDA-approved Lyme disease vaccine, LYMErix.

- There actually had been a vaccine back in the early 2000s that was pulled off the market because of low demand.

Once upon a time in the late There were some safety concerns with the vaccine but actually with post-marketing research and further surveillance, they found that those safety concerns actually did not pan out, it was a very safe vaccine.

It was just pulled off the market for other reasons.

There is a Lyme disease vaccine in clinical trials right now, so there may be a Lyme disease vaccine available for humans in the future, but we currently don't have a vaccine for Lyme disease for humans right now - Pfizer and Valneva are working together and are in stage three clinical trials for a new Lyme disease vaccine, VLA15, so stay tuned for more on that.

- We like folks to think about Lyme disease risk, as, you know, if you're potentially exposed, if you're not out there hiking and doing other things, you still could be infected just around your house, especially if you have trees and other green areas where ticks like to be.

- In the US, ticks are more active in the northeast parts of the Midwest and the Northern Pacific Coast.

Same with mosquitoes, who also love a good body of water.

But that might change.

And as cases of vector-borne diseases are rising, scientists and researchers are wondering what exactly is going on.

- As with most vector-borne diseases or all vector-borne diseases actually, there are so many factors that go into these vectors: where they are, how often they bite, what their activity is related to, you know, the day-to-day weather, the moisture, reforestation, as I mentioned.

So, and also animals, you know, animals that carry them around, the animals they feed on.

There are lots of different factors that go into the animals, the hosts that they use to take blood meals and have their ecologic cycles.

So I think that's why there are so many things that go into it.

That's why it can be difficult to tease out what's causing an increase here, what's causing maybe the certain vectors to have a different distribution.

- So whilst we might predict based on temperature alone where the pathogen can survive, what it's actually doing in real world circumstances That's why it can be difficult to tease out what's causing an increase here, might not be the same thing.

You can think of it like a Swiss cheese, kind of, stack of Swiss cheese layers where for that infection to occur, it has to go through the vector, through the host, to the person.

And at each one of those points, there might be barriers to infection, but yet we still have half the world's population at threat of a vector-borne disease.

- Recently, Dr. Eloise Skinner and a team published a paper in the science journal Nature about how they may be able to track the spread of vector-borne disease using machine learning, and they have a hypothesis about an indicator that might give us some insight about what is spreading these diseases: the human footprint.

- Humans, we're very good at modifying our environments.

We've done it for millennia.

And there are some estimates as much as 95% of the Earth's terrestrial surface has been changed in some way by people, which is just, like, mind blowing.

But essentially, to measure what those changes are and what pressure people put on the environment, another sort of research group has come up with the human footprint.

It's been around for a long time, but it looks at eight kind of cumulative pressures that people have on land.

It's like, the amount of built structures, the navigatable roads and waterways and agriculture, crops, air pollution.

So they basically layer on each of those per kilometer square across the world and can calculate a score from 0 to 50 on how much pressure people have put on the Earth's surface.

For the first time, we decided to use this human footprint to try and look at how just this one metric impacts the spread of vector-borne diseases.

Basically, we found in kind of forest and agricultural areas, diseases like malaria, visceral leishmaniasis, and cutaneous leishmaniasis were much more common.

And then as we transitioned to more pressure on land, we found diseases like dengue, Basically we found in kind of forest and agricultural areas, diseases like malaria, Chikungunya increasing in their prevalence.

And it was this really interesting, nice sort of shift from the dominance of one disease going down to the dominance of other diseases.

Ultimately, what you would want to be able to do with something like that is kind of referring back to where I was saying we prepared for shifts from malaria to dengue with changes in temperature.

If you could stand on the threshold of the changes from a forested area to an urban area and say, "Right, we're about to transition from one disease to another.

Are we prepared if we continue down the path of urbanization or reforestation?

Do we have the right public health tools and strategies to cope with these different diseases?"

(air whooshes) - Okay, you've been bitten.

There is a tick gnawing on you, enjoying a blood meal at your expense.

What do you do?

Well, the first thing you wanna do is find a pair of tweezers, preferably a small pointy kind, then grasp as close as you can to the skin near the tick's head.

Now what you wanna do is slowly and gently pull the tick out using consistent pressure.

Now, those ticks have some sharp barbs that can really dig deep into you, but don't panic, and do not twist or jerk as you're pulling that thing out.

With enough pressure, the tick loses and will pop right off.

And now you have two choices of what you wanna do with this unwelcome guest.

You can either put it in toilet paper and put it into the toilet for a watery grave, or you can put it in alcohol in a plastic bag or a piece of tape and send it in for testing, although the results may vary and the CDC recommends against using those results to decide whether or not you have an infection or should be taking antibiotics.

And please remember to treat any bite you may get with soap and water or alcohol.

Also, a word of advice: You wanna avoid those do-it-yourself remedies, like putting a flame on the tick or covering it in nail polish remover or alcohol.

The bacteria a tick may have is actually inside of its digestive system, and these remedies could cause a tick to regurgitate what is inside that gut into the bite that is on your skin.

No, thank you.

- It is important, if you do find an attached tick, it's important to remove it as soon as possible.

Some of the infections that are transmitted by ticks actually take some time to move from the tick gut up to the salivary glands and actually into the humans.

So for Borrelia burgdorferi, which is the bacteria that causes Lyme disease, it actually takes 36 to 48 hours to be transmitted by an attached tick.

- And if you have any questions or concerns, you wanna talk to a doctor, especially if it's been a few days and you notice any of the following symptoms, such as fatigue, fever, headache, muscle pain, joint pain, or a rash, specifically, that looks like a bullseye.

Lyme disease if left untreated can lead to some really debilitating symptoms, like facial paralysis, arthritis, even heart disease.

So if you have any concern about having Lyme disease, you wanna chat with a healthcare professional.

Someone will ask you some questions, do a physical exam, send out some lab tests, and if needed, start you on antibiotics.

So what you wanna do is be very vigilant anytime you go on a nature walk.

- For hiking and for other outdoor activities, as I mentioned, ticks really like that kind of shady, moist area.

The border between either forested areas or grassy areas and the more open, that's where they kind of stay on the plants and wave their little legs and try to attach to someone.

So if you're hiking or doing other activities, it's really best to try and stay in the middle of the trail and avoid those really brushy areas where the ticks like to be.

- One thing you should do is when you get home, take your clothes off and do a full body exam, looking in your hairs, your ears, your neck, your belly button, your arms, your waist, your legs, every nook and cranny, 'cause those little critters love those warm, moist spots on our bodies.

And one thing you should do is when you get home, take your clothes off and do a full body exam.

Okay, friends, still feeling itchy?

Because I definitely am and I feel like there's things crawling all over me.

Here's some advice.

The next time you head out to an area that is known for having fleas, ticks, or mosquitoes, you wanna try to use an Environmental-Protection-Agency-registered insect repellent with at least one of these active ingredients and make sure you wear long pants and long sleeves.

There's still a lot we're learning about vector-borne diseases and why they're rising, but in the meantime, we can do our best to stay safe out there.

And that's it for this critter-filled episode of PBS Vitals.

In the meantime, even though there are things out here that wanna drink your blood, literally, be sure to still enjoy nature.