A new Lyme test for horses holds promise in humans — and dogs

The veterinarians were puzzled. They had a horse that was clearly sick, but they didn’t know why.

This wasn’t just any horse. It was a performance horse, preparing for competition. (For those in the horse world, we’re talking about an 11-year-old Swedish Warmblood mare.)

The veterinarians suspected neurologic Lyme disease, but couldn’t confirm.

It just so happened that researchers at Rutgers New Jersey Medical School and University of Maryland, led by Steven Schutzer, a Rutgers professor of medicine, were working to refine a new method to detect the disease.

Schutzer’s team tested the spinal fluid of the horse, and sure enough, it was Lyme.

This new test holds promise for humans — and dogs, too. It’s about time. Lyme is the most common vector-borne illness in the U.S. Based on insurance records, the Centers for Disease Control and Prevention has estimates 476,000 people are diagnosed with Lyme every year. The disease is particularly prevalent in Southeastern Pennsylvania.

Most cases can be treated with a few weeks of antibiotics, the CDC says. But early detection is important. If left untreated, what began as a fever, headache, fatigue, and a rash can progress to affect the nervous system, joints, and heart.

They are serology antibody tests, tests that look for antibodies in a person’s blood that might indicate infection with Lyme. They are the only ones approved by the U.S. Food and Drug Administration. (Patients who have been tested may be familiar with two test names — ELISA and Western Blot. Although slightly different, both are serology antibody tests.)

But these tests are indirect — measuring only the body’s response to exposure to Borrelia burgdorferi, the microbe that causes the disease. So the antibody tests do not indicate active disease. They can only tell you, in the best circumstances, that you’ve been exposed to the microbe. It doesn’t tell you when. Is it right now, or a year ago, or five years ago?

Another problem with the antibody tests is a high rate of false negatives if they are used too early in the first couple of weeks of the infection.

We were working on a DNA test. With that, you are searching for parts of the microbe itself, specifically the DNA. So we oriented the test to target just Borrelia burgdoferi DNA. If you find the DNA of Borrelia circulating in your blood or spinal fluid, you almost certainly have active Lyme disease.

This type of test and other DNA tests are not yet FDA-approved for humans, but it is being used in some research settings and clinical labs.

One advantage of this test is that it’s the same, whether you’re testing a horse, a dog, or a human. You’re looking for the DNA of the microbe, not antibodies. Antibodies are specific to the host. Dog antibodies and horse antibodies might be different from human antibodies.

But the shortcoming of DNA tests in general, in the case of Lyme disease, is that in whatever sample you have — blood, spinal fluid — there may be very few copies of the DNA you’re looking for. The nature of the Lyme agent is that it is not in abundance in the body’s tissues. Its DNA is not all over the place. Whereas if you had a common viral infection, that’s easy to find if it’s there.

So you want to do things that seem to enrich that specific target — in the sea of the host DNA — so you can determine whether it’s there. That’s what we were doing in our research.

Let’s say you go to the beach and you want to find pink grains of sand where otherwise the beach seems white. Consider the pink grains to represent the pathogenic microbe. So it would be good if you could do something to increase the relative number of pink grains of sand in your sample. Maybe by getting rid of a lot of white sand, which leaves, in proportion, more pink grains of sand. Or imagine if you had a specific hook to grab only pink sand, even if it’s hard to see. Then you’ve got a better chance of finding the pink sand — or, in this case, the DNA of the microbes — if you apply a test.

We were working to see if we could isolate those pink grains of sand, those microbes.

While we were doing this, one of our veterinary colleagues at Cornell University’s College of Veterinary Medicine in New York told us about an interesting case of what they thought was neurologic Lyme disease in a horse affecting its brain. It turns out that central nervous system neurologic Lyme in a horse is rarely definitively confirmed until the horse dies and they do a necropsy. It has bedeviled veterinarians for years.

With humans, you need special permission to involve them in a research study. You need their approval. We didn’t need that for a horse. The owners can give the permission. So they gave us some spinal fluid, and we tested it. And we found the very specific DNA of the offending microbes — Borrelia burgdorferi.

By treating the horse, veterinarians were able to return the animal to athletic high performance status.

The Cornell veterinarians also sent us spinal fluid from another horse that had been treated for neurologic Lyme disease and was well on its way to recovery. In theory, if you eradicated the infection, the DNA of microbes should no longer be detectable in the spinal fluid. And sure enough, we didn’t find any.

This was a convergence — specialists in veterinary medicine and human medicine sharing information.

[Thomas Divers, the veterinarian who led the equine team at Cornell, and Schutzer coauthored a paper on the study, which was recently published in the Journal of Veterinary Diagnostic Investigation.]

Yes. It holds promise. It also holds promise for use in dogs, which also get Lyme disease.

We hope it could be another diagnostic arrow in the quiver, a better test to be applied to detecting active Lyme disease.

One obvious thing is to refine the test in the laboratory. We can work on making tweaks to make the test more effective.

But the real thing is getting more numbers in the next couple of seasons, increasing the numbers of cases so your research colleagues, the medical community and the regulatory agencies believe it is working and is an improvement.

We hope to do that.