It’s Tick Season Again: From the Archives

As North America heats up for summer, so does the activity of ticks, mosquitoes, and fleas, whose bites can carry diseases like Lyme, dengue and Zika, and plague. Between 2004 and 2016, more than 640,000 cases of these diseases were reported, and nine new germs spread by bites from infected mosquitoes and ticks were discovered or introduced in the US, according to the Centers for Disease Control (CDC).


Image: Centers for Disease Control and Prevention

May is  Lyme Disease Awareness Month; people who become infected risk long-term problems with skin, heart, and joints–and brain. The disease can cause cognitive and memory impairment, headaches, neuropathic pain, facial palsies, encephalitis, and seizures.

Microbiologist and former Dana grantee Mark Wooten, at the University of Toledo, studies how the Lyme-triggering bacterium Borrelia burgdorferi, carried by ticks, interacts with the mammalian immune system. He credits growing up on a farm in Arkansas, in an area with a lot of ticks, with piquing his interest in Lyme disease, which was then a relatively new discovery. He talked with us last year about what makes this bacterium so tricky:

To infect an animal, B. burgdorferi has developed very unique methods, many of which we still don’t understand. But those methods allow it to become almost invisible to the host animal’s immune system. Its host animals are completely immunocompetent, meaning they have a perfectly normal immune response where the immune cells become activated soon after detecting the bacteria and go to the site of infection. Within a few days’ time, they will also develop antibodies and do all of the things that would normally clear an infection. But these bacteria are not cleared and continue to persist out in the extracellular spaces where they should be exposed to these immune mediators. Somehow the bacterium is adapting in the host to become nearly invisible to the immune response—and that’s what allows it to persist for so long.

He wanted to study this process more closely, which meant finding ways to watch it in action in living tissue. He and his colleagues have developed new methods of making the bacterium fluorescent and then tracking them through body spaces:

When we measured them, they moved around 100 times faster than any other immune cell type that we measured traveling through the skin tissue. And, unfortunately, something moving that fast is really hard to image. With an immune cell, you can take an entire z-stack of images with a confocal microscope to get a three-dimensional image of the cells in a tissue. And you can take one of those every three to five minutes, stitching them together to make a nice video that shows you how immune cells move. But this bacterium moves too fast. You try to get the z-stack images and combine them, but you end up with just one big bacterial blur, while the slower immune cells look fine. We’ve had to work out the best way to measure B. burgdorferi—and how to image it and still get accurate measurements of how fast it moves. This is an obstacle we are still dealing with. It takes a lot of time and patience.

Research such as this is sorely needed, as well as good public planning for stopping infections before they start. Wooten says:

Lyme is a very complex disease, because the bacteria want to be invisible. They want to get along so they can survive. And Lyme disease is our immune response refusing to ignore these bacteria—and trying to fight them off with an inflammatory response. And since it is the body’s own response, it leaves us with a big problem. Often Lyme disease isn’t diagnosed right away. It may not be diagnosed until you see some of the more advanced severe symptoms. You may be having this health issue—but are you going to connect it with a tick bite you probably don’t remember even getting from 2-5 months ago and then tell your doctor about that? Probably not. So better diagnosis and diagnostics are a big public health issue. This is because if you wait until the severe symptoms have developed, even if you clear the bacteria with antibiotics, a lot of damage has already been done. Then the next question becomes how do we heal people who have suffered neurologic, or other damage, once we cure the infection? Unfortunately, many of these tissues do not heal quickly or may not heal completely at all.

What can we do? The CDC has many recommendations, including these we all can do:

There’s much more in our Q&A with Dr. Wooten, including what we’re learning in general about inflammation and brain disorders and how gene-editing techniques like CRISPR could change this field.

– Nicky Penttila

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