Reality check on Lyme in New England

How common are high Lyme titers in New England? I am looking at a horse and received the vet records that show raised titer levels for OSPA and OSPF on two multiplex assay tests several years ago (OSPF level dropped for second test about a year after the first but still positive, neither are off the charts high). The horse has been vaccinated for Lyme.

The horse is in New England, where Lyme is endemic. I have not had titers taken on other horses, and for all I know every horse in New England could have positive titers at some point during the year. The owner did not disclose the test results to me, but has been straightforward about other medical concerns and the horse is currently sound and has no history of lameness. I am not sure if this is something to be concerned about or just par for the course and somewhat expected in the Northeast. Thanks for your insights!

We’ve lived here for five years. All my horses have a positive titer and I usually have to treat at least one of them every year, despite good tick protection and damned near never finding a tick on them. I’ve also had Lyme myself a couple times, even with being VERY careful.

Don’t think you’re going to find a horse here without a titer. Worry about symptoms.


Simkie’s right about how endemic the disease is in the region, such virtually all horses who’ve lived here for any length of time have probably been exposed. (Perhaps too sweeping of a statement, but it’s just so common here).

And yes also to the point that you need to worry more about symptoms. But now for the big BUT…

Sometimes the symptoms can be initially so mild that no one really notices them. A horse can be slightly off for a couple of days and people will think that there’s a slight stone bruise, or may have a slight fever that no one notices, or seems a little lethargic for a few days.

And then, a couple of weeks/months later a much more significant set of symptoms will blow up and you have a real problem.

My best advice would be to talk to the vet and maybe even pay for a second opinion. I wouldn’t not buy a horse just on the titer results (unless they showed an active infection), but I’d do a pretty close scrutiny of the horse in every way before making the decision.

I’ve been in NH/VT since 2010. My vet always said- let me pull blood on a random field of 10 horses, 9 out of 10 will come back either chronic or acute. I’ve treated all three of mine for chronic.

Last time I did a PPE, back in 2018, I ran Lyme on the horse just because I wanted to know. Owner was surprised I bothered because she was totally asymptomatic. But the reason I was in the market was because I had just retired my older mare after she had a difficult case of Lyme and didn’t ever really regain her topline despite aggressive treatment- given that experience, I wanted to know what I was looking at with a potential new horse. Sure enough, the horse I was looking at came back positive for both chronic and acute. I agonized about it but still moved forward with the purchase; seller reduced the purchase price to account for the round of treatment I would do when I got the new horse home (my vet at the time used a protocol of 5-days IV oxytet followed by a month of oral doxy and then retest with multiplex). The new horse recovered well and didn’t have any limitations. I do vaccinate all three of mine annually at this point.

All that to say- not surprising the horse you’re looking at tests positive. It’s a bit of a gamble about what it means for the individual horse now and in the future, but odds are if you pass and PPE another one, you’ll be looking at the same thing.

1 Like

You’re vaccinating horses that have been positive & treated previously? How’s that working?

I really wish I’d vaccinated my (Lyme naive) horses before moving here, but that ship has long since sailed. I was considering the vaccine now, but there’s just so little data and I worry about potential for harm. But man does it suck dealing with it :frowning:

I know, it sounds weird. Like you said, there’s so little data it’s essentially a “probably won’t hurt, might just help” sort of move. Whether it’s just dumb luck or actual vaccine protection, I haven’t had any positive tests since taking this approach, nor any symptomatic issues. And the horses definitely have ticks on them most of the spring (as do I). We also haven’t had any vax reactions.

My current vet recommends it, my previous vet wouldn’t touch the vaccine for off-label equine use. I guess you make the best decision you can.


I assume it is Zoetis? I do not know if there are any others. How may doses do you get? A vet from Zoetis told me you need three doses of their dog vax off label for horses. And how much is in each dose?

@Snowdenfarm- Current vet starts you off with a 3-shot series (I’m forgetting the number of weeks apart as this was a few years ago) followed with bi-annual “boosters” in the fall and spring. She organizes mobile Lyme clinic weekends with discounted rates for the boosters. This fall each shot was $45/horse plus a $12 farm call. I do not see the manufacturer name on my most recent bill.

1 Like

Another reason to pull a titer on an asymptomatic horse is that it can give you a baseline. I had a horse that for years was in the ‘chronic’ Lyme group. We treated him when he was symptomatic only. We first tried, of course, to get the titer all the way down. Months of doxy aren’t a good idea for anybody! So, eventually we would treat till the symptoms were gone and the titer was back to his normal. I have no doubt that is not the best thing to do given antibiotic resistance, but it was what several vets concurred on. It was either that or doxycycline for the rest of his life.
My current vet won’t give the vaccine, as it is off label. But, I used to give it. It was a useful addendum in the ‘can’t hurt’ category.


Yup. We pull Lyme at PPE, and at least once a year thereafter. I’ve only had one horse come back with no exposure at all.

1 Like

@MorganMaresVT no, not weird at all! That’s awesome you’ve had good results, thanks for the details on how you’re using it.

I was really leaning that way earlier this year, but read some troubling thoughts about vaccinating post Lyme exposure. I wish there was just more information & study out there!


What kind of issues did you read about with vax after exposure? Any links? I am seriously considering it, but did not know there were reasons not to.

I live in Maine and keep my horse in a locale that has high incidence of Lyme. I tested and treated my last horse after years of NQR moments. I wish I had checked that out sooner, but it also didn’t totally eliminate his NQR-ness, so there was more going on than just Lyme. Anyway, I wanted to chime in to say that our vets definitely recommend vaccinating, and, as mentioned above, initially it’s three shots one month apart and then biannual boosters in the spring and fall. We’ve had good luck with the vaccines; it’s been years since we’ve had a horse on the farm that has been symptomatic enough to warrant treatment.


I posted about it here:

My horse is vaccinated for Lyme and has been for the past 3 years.
I only trail ride, am in MA and am constantly pulling ticks off.

Here’s his test results from May 2020 with the explanation.
To summarize, high OspA with low OspC and low OspF means the good antibodies.
High OspA and high OspC or OspF potentially means infection.

Details below:

Lyme Dis. Equine - Multiplex The Lyme multiplex assay determines antibodies to three antigens , called ‘outer surface proteins (Osp)’, of B.
burgdorferi which have been shown to correlate with vaccinal antibodies, or acute and chronic stages of Lyme disease.
Negative: Negative values for antibodies to all three Osp antigens are predictive that the horse is not infected. If only one or two values are in the negative
range see interpretation for equivocal or positive values for the corresponding Osp antigen.
Equivocal: Equivocal values can indicate very early infection or can be induced by non-specific serum reactions. If there are no positive values for any of the
three Osp antigens, the horse should be retested in 2-3 weeks to confirm or exclude early infection. If one or two values are in the positive range see
interpretation for positive values for that corresponding Osp antigen.
Positive/ OspA (>2000 - 28,000): Positive values for antibodies to OspA are typically observed in vaccinated animals . In horses, however, antibodies to OspA
also seem to rise during infection. Thus, the interpretation of results on antibodies to OspA is more complex in horses . If antibodies to OspC and/or OspF are
positive, along with OspA, the horse should be considered as infected with B. burgdorferi.

Positive/OspC (>1000 - 10,000): Positive values for antibodies to OspC only are indicative for early infection. Antibody values to OspA can also be elevated
during early infection.
Positive/OspF (>1250 - 26,000): Positive values for antibodies to OspF only are predictive for chronic infection stages. Positive values for antibodies to OspC
and OspF in the same sample are indicators for an infection that occurred several weeks ago and is moving towards the chronic infection stage.
This assay is validated and accredited for the detection of antibodies to three Borrelia burgdorferi antigens in equine serum

FWIW, we also routinely vaccinate 4 horses who were positive and treated, some of them multiple times as they had gone chronic before the infections were ID’d. I believe this year was year 9 of annual vaccination for the older horses (year 7 and year 2 for the younger ones - they have been done annually since purchase).

Initially, I was using the Merial dog vaccine, but have used the Zoetis one in recent years.

ETA: all but the youngest horse have been treated for Lyme at least once.

We vaxx all ours and we frontline everything three weeks.

We also put off in every fly spray bottle.

Lymes is horrid as are all the other tick borne illnesses.

I’m not 100% sure but I think that horses who have been vaccinated will have higher titter numbers. Maybe someone with more knowledge can answer that more positively.

Those who vax, do you do it in the spring?