There are two articles here, with slightly different takes on this.

First article:
https://rawlsmd.com/health-articles/can-stevia-treat-lyme-disease

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Why Can’t Stevia Treat Lyme Disease?
by Dr. Bill Rawls - Updated 8/27/18

Lately, there’s been a lot of talk about stevia being beneficial for treating Lyme disease. This comes from an in vitro study published in the European Journal of Microbiology and Immunology in November of 2015. The study found that whole leaf stevia extract effectively kills Borrelia burgdorferi spirochetes and cyst forms.

Ever since the study came out, there has been widespread talk on the web about using stevia to treat Lyme disease. One company, founded by a Lyme expert, has even been promoting a stevia product specifically for treating Lyme disease.

Unfortunately, the reasoning is highly flawed.

The operative word here is, “in vitro”. In vitro means that the test was conducted in the lab. When placed in a test tube, whole leaf stevia extract inhibits growth of live Borrelia spirochetes and cysts.

This does not mean that it kills Borrelia in living organisms. To treat Lyme disease, the chemical compounds present in stevia must be absorbed through the intestines — but the reason it works so well as a sweetener is because these substances are not absorbed through the intestines. This fact has been well documented by numerous scientific studies.

Therefore stevia extract wouldn’t be expected to provide any significant systemic antimicrobial activity against Borrelia or any other microbes associated with Lyme disease.
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But that's not necessarily the end of the story. Stevia glycosides do break down in the gut, into some sugars and a compound called steviol, shown in red:

It turns out that the steviol breakdown product is absorbed in the intestine. But the information on activity in vitro was for the steviol glycosides (like the whole molecule above). I don't think anyone has tested steviol itself for anti-Lyme activity. It would be a good thing to do.

Abstract on Stevia metabolism:
https://www.ncbi.nlm.nih.gov/pubmed/12738193