As West Nile mosquitoes thrive in the metro, an expert offers protective tips

Human health doesn’t exist in a vacuum. We’re impacted by everything in our immediate surroundings, from the catastrophic effects of weather to the tiniest bug bite. 

The Metropolitan Mosquito Control District operates in the seven Twin Cities metro counties, trapping mosquitoes and ticks for analysis and testing them for pathogens like West Nile virus and Lyme disease. The data allows the MMCD to take safety measures, including chemical interventions to target developing larvae or adult insects.

Each week from mid-May to September, the MMCD releases an update. Recently, tests showed a surge in Culex tarsalis mosquitoes carrying West Nile virus, putting Minnesota and the greater Midwest at increased risk for West Nile virus transmission. 

MinnPost spoke with Jordan Mandli, Ph.D., MMCD’s vector ecologist, about how diseases are transmitted by mosquitoes and ticks, as well as how we can protect ourselves from disease. This interview has been edited for length and clarity. 

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MinnPost: What drew you to vector ecology and to insects in particular? 

Jordan Mandli: I like to say it’s all happenstance, but it was really kind of the culmination of a lot of experiences. As a kid, I was really into the outdoors. As I started trying to figure out what I wanted to do as a professional career, I started to recognize certain patterns. What really drew me to the vector-borne disease side of things – beyond having been fortunate to be given the opportunity to work with researchers in this area – was that these are diseases that are transmitted by different arthropods, whether it be ticks, flies, mosquitoes. These diseases have kind of a second life, where they’re naturally circulating within the environment. A tick gets infected by feeding on an infected mouse, and that infected mouse got infected by a tick. The cycle that keeps continuing and expanding. You bring the human element into that and it becomes this very weird relationship, where all of a sudden, as we expand into new areas, or as animals are moved out of their habitat, disease starts to spill over. That idea that something that’s so natural can have such detrimental effects on human and animal health – it’s very cool to me.

MP: How does the transmission of disease through vectors like mosquitoes or ticks work? 

JM: An arthropod is infected – say it’s a mosquito. It’ll feed on a bird. We’ll focus on the West Nile virus scenario here. That bird becomes infected, and assuming that that bird doesn’t die, it’ll start getting more and more virus in its bloodstream, and it’ll become a food source for many other mosquitoes. Because most mosquitoes will feed multiple times once they’ve been infected, any subsequent thing that they run into, they’ll have the potential to infect. That might be more birds, it might be a human. 

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When we think about vector-borne disease, a lot of people will talk about how climate change may be modifying the impact of mosquito-borne diseases. When things get hot, mosquitoes mature faster. The pathogens inside of them are going to replicate faster. So our first instinct is to be like, ‘Yeah, there should be a ton more disease.’

The hard part about that is we have to take into account other considerations there, including the human element. And the human element is a really challenging one because when it’s hot outside, I’m not going to be outside. I want to be inside enjoying the air conditioning. If the air quality index is really high I might be inside, away from mosquitoes. They’ve done studies along the Mexico and Texas border looking at communities that are at the exact same latitude, exposed to the same mosquitoes coming from the same river valley. People on the American side have lower cases of disease, and the real reason for that is because they have better barriers in their home – screens and air conditioning.

MP: You’ve mentioned how mosquitoes are impacted by climate change and warming temperature specifically. What about ticks? 

JM: As things get warmer, ticks are going to show up earlier in the season. As we’re starting to see more extreme temperatures due to climate change, we’re going to see ticks become more common throughout the entire year. 

Here in Minnesota, [the blacklegged tick, also known as the deer tick]can be active as long as it’s about 40 degrees and there’s no snow on the ground. As climate change creates more of those ideal conditions, we’ll certainly see more activity of those ticks, and then people will be more likely to get sick at those times. 

Some tick species are more likely to dry out. So if things are really hot and dry, that’s not great for them. The same thing kind of goes with mosquitoes. A mosquito, to complete its life cycle, needs water. Certain species lay their eggs in areas where they know water is going to be and when the water rises, it causes them to hatch. When water doesn’t reach that point, the eggs continue to persist. And they can persist up to 12 years. The viability of those eggs declines pretty dramatically in those later years. But think about the accumulation of eggs, what we call the egg bank. You can have years where the conditions are just wet and just hot enough. That’s why we get such large numbers of mosquitoes.

MP: Is there anything that people can do to reduce their chances of becoming infected by a mosquito or a tick? 

JM: Things that you can do to your actual property on the mosquito side of things – dump any water from containers on a weekly basis. Go around your property, see where you’re holding water. Dump it. If you can’t dump it, there are products out there called mosquito dunks. You can add those to those semi-permanent water sources, and that should kill any mosquitoes that try to breed in those spaces. Another thing you can do is make sure things around your home are being maintained, like the screens on your windows. 

Then there’s physical boundaries. When you are out enjoying your backyard this time of year, it’s really hard to not be out there in short sleeves, but during those dusk hours when we know mosquitoes are going to start to pick up, wearing pants and wearing long sleeves is going to really minimize your risk, with the addition of repellents. You can use some spatial repellent products, but depending on what kind of home you have – if there’s a lot of wind coming through it –  some of those products may not work as well.

When it comes to ticks, it’s like mosquitoes. Using repellents, wearing long sleeves, wearing pants. Know what’s good tick habitat – don’t go traipsing through the woods unless you have to. Stay on the trails if you’re going for a nice hike. Staying to the center of the trail minimizes your risk substantially. I know it’s not the coolest thing in the world, but tucking your socks into your pants. Treating your pets with Fipronil or other topical products that will kill ticks that get on them will prevent them bringing ticks into your house. 

Do a tick check – getting someone to check you in the places on your body that you can’t see, but also checking yourself. We usually encourage people, once you get home from being out somewhere where you know there are ticks, to strip down, put your clothes in the dryer, run 10 minutes on high — this will  kill anything that’s still on there — and then to take a shower. A shower is a great opportunity to wash off any ticks that haven’t actually attached to you, but you’re also more likely to see if a tick has attached during that time. 

Around the home, there are a lot of products out there that you can utilize. There are tick tubes – cardboard tubes that have cotton that’s treated with a pesticide. Mice will come and take the cotton and it treats the mice [for ticks]. They work fairly well – but if you don’t have mice in your area that are contributing to disease transmission, they’re not going to do much.

It’s also about keeping infected reservoir hosts out of your backyard. If you’ve collected wood for the winter, move that pile of wood away from your home or anywhere you’re going to be more active. Keep your yard well groomed – remove leaves and mow on a relatively frequent basis. Anytime where there’s a lot of sun exposure, ticks are going to die. If you have a jungle gym in your backyard, get it away from the forest edge. If you’re anywhere where there’s deer, and it’s not an uncommon situation here in Minnesota, fences can keep the deer out of your backyard. 

MP: Do you have any fun facts about ticks or mosquitoes? 

JM: Deer ticks don’t have eyes. Their sensory organs are found on their front set of legs. So they’ll sense something by using either heat, CO₂, or a change in rhythm. As you’re going by you might brush something so it shakes and the deer ticks are just hanging out there. When you happen to go by, they reach out and grab on, so they don’t really fly or anything. 

Deer ticks can also transmit quite a few different diseases here in Minnesota. If you get bit by a tick, there can be upwards of seven different pathogens that can be transmitted by a deer tick. In some places, up to 50% of those ticks are infected with one of those pathogens. The reality is that ticks can also have all of those pathogens. So a single tick bite might mean that you get infected with all seven or five or whatnot. 

Editor’s note: This article originally appeared on MinnPost and was written by Deanna Pistono, MinnPost’s race and health equity fellow. It is republished here under a Creative Commons Attribution-NoDerivatives 4.0 International License.

MinnPost is a nonprofit, nonpartisan media organization whose mission is to provide high-quality journalism for people who care about Minnesota.