Lyme Disease May Cause Sudden Aggression in Dogs
Written by Betsy Sommers of
Peppertree Rescue, Albany, NY, USA.
28th May 2004: We recently had a very strange event that I think we should share around
the rescue community.
A Young (~2 years) Lab mix, male, came into our program with a
"questionable" background. He may have been aggressive toward some
children, maybe not. We kept him for a good long while, months of
fostering in our premier foster home, with no problem and placed him
carefully, with a single mid-age man who absolutely adored him. We also,
as we do with all our dogs, tested him for Lyme. He had it so we treated
it; case closed we thought.
Everything went very well after adoption. He was the star of his
obedience classes, a frequent alumni visitor to our clinics for over
a year, and truly adored by his adopter. Then, over a year after
placement, Mojo became suddenly, erratically, and seriously aggressive,
literally attacked visitors to the home, people at the vet's waiting
room, etc. Terrifying. Very sudden. Totally inexplicable. He was
returned to us with genuine heartbreak from a very loving adopter.
Mojo then went to our regular vets and was a totally different dog,
bared teeth and growling to anyone who approached his kennel, lunging at
other dogs when being walked, etc. We figured that whatever was
happening with him, he had become implacable and started a TDC (Tough
Decisions Committee - something we "convene" and that is open to anyone
with an interest in the dog when we think that euthanasia might be an
However, someone at the vet's office said that perhaps we should test
him for Lyme. Huh? They had had a regular client of theirs come
in recently with similar, out of the blue aggression, and it turned out
that was the problem, it puzzled them, but seemed to be the case. Okay,
we'll try anything, so we had him tested. He was high
positive! Fine, we started treatment while we continued to figure out
what to do with him via the TDC. Almost immediately, however, once the
antibiotics were begun, the Mojo we knew came back! He was himself
again - bouncy, happy, a bit neurotic, but not at *all* aggressive!
The staff at the vet's was amazed, but all confirmed this change.
We didn't believe it; and the veterinarians didn't believe it BUT a
thorough search of the Internet turned up a number of studies and
anecdotal observations indicating that in some dogs (and in some
humans) the primary symptom of their Lyme Disease can be sudden,
irrational and serious aggression. Well, we've known for a while to
check the thyroid levels of dogs that show aggression that just "doesn't fit".
Now we have added testing for Lyme as well. And we have - results not
yet in - another dog that we placed over a year ago who has been
returned because of out-of-the-blue aggression and he has also
tested high positive for Lyme! We've started treatment and will be
monitoring his response.
So plug this in to your protocols. It's worth checking out. I
spent the day today with Mojo and he truly is just the same dog we
placed over a year ago. We've let his original adopter know because
he vowed that it had to be 'something' causing this behavior. But he
cannot take Mojo back because his roommate, one of the people attacked,
won't even consider it. For the record, there were no skin-breaking
contacts in any of these attacks, but plenty of fear and we consider
them as serious as if they were full-fledged bites. We actually have
additional insight into this because one of our volunteers (human) has
had Lyme Disease. It took many months for her to be diagnosed, and once
she was, she learned that it's a VERY nasty bug that really remains
around permanently, waiting for a chance to "crop up" again. When we
place Mojo again (and our TDC unanimously agrees that we should do
this), we're going to explain the background, these amazing events, and
require that the adopters have him tested every six months, whether or not he's showing
symptoms. We have no idea whether that will work or be sufficient,
we're rather flying blind in this, but it seems a rational
I'll post again if we learn more from the second dog (also a Lab mix).
But based on what we know now, it is a real possibility: Lyme *can*, in
a few rare cases, cause aggression, aggression that can be reversed.
Page updated: 24th March 2017