Summer of rain paving the way for a mosquito boom, but not until next summer

NINA MOINI: Well, this is Minnesota Now. I'm Nina Moini in for Cathy Wurzer. Mid-July means we're deep into mosquito season. And since mosquitoes thrive in puddles of standing water, the huge amount of rain we saw in June is paving the way for their populations to boom.

That's concerning for researchers who are seeing a rise in insect-borne diseases across the state. And they think climate change could have a hand in it. Joining me now to explain are two people who spend a lot of their time thinking about this potentially growing threat from insects like mosquitoes and ticks. Jonathan Oliver is an entomologist and professor at the University of Minnesota's Division of Environmental Health Sciences and Alex Carlson manages public affairs with the Metropolitan Mosquito Control District. Jonathan and Alex, thank you for being here.

ALEX CARLSON: Thank you, Nina.

JONATHAN OLIVER: Yeah, I'm glad to be here. Thanks.

NINA MOINI: Well, wow, Alex. Let me start with you. We know that mosquitoes thrive in that standing water. And there's a lot of that around. Even as I take my dog out for walks, I see a lot of that. And I think those are mosquitoes coming for us. So does all of this rain and flooding in the state automatically mean more mosquitoes?

ALEX CARLSON: Usually it does. The advantage that we have this year is we're coming off of three years of drought. And so the overall numbers have really been hit pretty bad by a lot of years without rain that was hatching those eggs. So some of the more common summer mosquitoes aren't as abundant as they would be with the amount of rain that we're seeing.

NINA MOINI: OK. So just out of curiosity, how does the Metropolitan Mosquito Control District go about finding and testing mosquitoes for viruses?

ALEX CARLSON: Well, what we do is we set up traps throughout the Twin Cities to do adult mosquito collections. So we set up CO2 traps which give out a small amount of CO2 to mimic a person's breathing. And we also do some other forms of collections to get adult mosquitoes. And then we take those back and we identify them by species. And then we determine if they need to be tested for potential disease, if they're one of the vectors that could be spreading West Nile Virus or some other diseases.

So we set about 200 traps. We also have human volunteers who get to go be bait and stand out with our sweep nets and let the mosquitoes come to us and then collect them with our nets and bring those back as well.

NINA MOINI: OK. That sounds like a fun job. So, Alex, I understand that some mosquitoes in Anoka County did test positive for West Nile Virus in just mid-June. How alarming is that?

ALEX CARLSON: Every year we collect mosquitoes that end up testing positive for West Nile. So we really we look for the abundance and the timing. It's a little bit earlier than the average, which is around mid-June. We've also tested some that have come back positive in Dakota County that were just collected last week.

And so it's not surprising given the warm and wet spring that we've had. But it does get concerning. I mean, the risk for mosquito-borne disease escalates as the summer goes on, especially in Minnesota here. So West Nile risk tends to escalate as we head into July and August.

So it's just an important reminder that people take those precautions. Put on the bug spray. Cover up. And empty out any standing water, of which there's a lot, as you mentioned.

NINA MOINI: Yeah. Now, Jonathan, from a public health standpoint, how do you raise awareness around West Nile Virus but not overly alarm people?

JONATHAN OLIVER: Yeah. So MMCD does a great job at disseminating information about West Nile Virus. Their website has up-to-date info on mosquito abundance and locations. And they have maps and all that. So they do a really good job at disseminating that information.

Similarly, Minnesota Department of Health also has good statistics over time for what the trends in various vector borne diseases have been in the state.

NINA MOINI: OK. So it's always going to make headlines if something like that is found, but making sure that we're putting that into perspective for people. And Jonathan, I also wanted to talk to you about ticks. How has our state's recent sort of abnormal climate affected those populations?

JONATHAN OLIVER: Yeah. So deer ticks are the main species that people should be concerned about when it comes to disease transmission risk. And deer ticks tend to be pretty limited to higher humidity habitats. That's why we normally find them in forested areas. There's damp soil and high humidity for them to find a refuge in during the heat of the day. So the wet weather this year has definitely been a benefit for the ticks, especially those immature ticks have been coming out in high numbers.

When we're talking about the nymphal stage, that's one of the immature stages of ticks where they're about as big as a poppy seed. Those nymphs peak in activity in June. And so we're kind of on the trailing end of nymph activity. But they're still out there. And the wet weather is helping them maintain their activity.

NINA MOINI: Sure So how do you expect then, Jonathan, that the rest of the summer could affect that population?

JONATHAN OLIVER: So like I mentioned, the immature nymphal stage, which is the most concerning in terms of disease transmission peaks in June. And so if the weather continues to warm up and especially if it dries out, we'll probably end up with not a lot of ticks until we get adults coming back out in the fall.

NINA MOINI: Oh, that's interesting.

JONATHAN OLIVER: We're kind of getting towards the end of tick season at this point.

NINA MOINI: OK. Well, let's talk really quick about the changing population affecting the diseases that humans get from ticks, like Lyme disease.

JONATHAN OLIVER: Yeah. So there are seven different diseases transmitted by deer ticks in Minnesota. And Lyme disease is by far the most common. Depending on what life stage of ticks you're talking about, like, if you're talking about these nymphs, or if you're talking about adults, and then depending on the specific location you find the ticks, anywhere from about a quarter to half of ticks have the bacteria that cause Lyme disease present in them. So it is quite abundant.

In the last 30 years, ticks have really spread to all of the forested counties of the state and are even being found in isolated forested areas, kind of like islands out in the prairie parts of the state. So they've really become widespread in the last 30 years.

NINA MOINI: OK. So something we do kind of need to be on the lookout for. And in that vein, what are some tips for avoiding disease from ticks?

JONATHAN OLIVER: Yeah, right. So prevention is definitely a key to avoiding tick-borne diseases. So we recommend wearing effective insect repellent, such as those that contain DEET or other EPA-registered repellents. Being aware of when you're going into tick habitat and what time of year it is in terms of what ticks you're likely to find is also very important, just being educated.

And another real great preventative measure is doing daily tick checks. It takes at least 24 hours after a deer tick bites for Lyme disease to be transmitted from the body of the tick into your body. And so if you do daily tick checks where you carefully check your whole body for ticks and then remove any ticks that are found, that goes a long way towards mitigating risk.

NINA MOINI: And are you saying that for every day, or just if you happen to have been outside, or do you think it's worth doing every day?

JONATHAN OLIVER: I would do it every day when you may have been exposed to tick habitat.

NINA MOINI: Got it.

JONATHAN OLIVER: So every day when you're into brush or wooded areas, especially.

NINA MOINI: Got it. And Alex, we know it's going to be hot this weekend. People are going to be in the sun. And the bugs are going to be out. So how do you suggest people avoid mosquito bites when they're outdoors?

ALEX CARLSON: Yeah. It's a lot of the same recommendations for ticks. You cover up your skin. We say long, light, loose, long sleeves, light colors, loose fitting. Wear that bug spray.

And just avoid those peak times. They're not as active when it's sunny out. They're vampires. They drink blood, and they like the shade. They like the dark.

So just avoid outdoor activity during their peak feeding hours. And that'll go a long way, too. And then do anything you can to help reduce their habitat. So just removing that standing water and calling us if you're noticing additional standing water areas that shouldn't be there.

NINA MOINI: All right. Well, Jonathan and Alex, I want to thank you both so much for coming on and sharing your knowledge with us. I really appreciate it.

ALEX CARLSON: Thank you.

JONATHAN OLIVER: Yeah, thanks for having me.

NINA MOINI: That was Jonathan Oliver, an entomologist and professor at the University of Minnesota's Division of Environmental Health Sciences, and Alex Carlson, who is Public Affairs Manager with the Metropolitan Mosquito Control District.