Ehrlichia, ticks and the case of the elusive Christmas Eve diagnosis
Posted Jan 07 2009 4:31pm
Christmas Eve is not the best day of the year to come down with any illness that eludes obvious diagnosis. That’s what happened to the eight year-old Rottweiler who arrived as a last-minute emergency before we closed for last week’s holiday.
When she arrived, Trixie had been restless and uncomfortable overnight. Her owners suspected a serious flare-up of her arthritis and were seeking some powerful pain relievers. But Trixie’s limbs seemed no more painful to me than usual. Her back, however, was more sensitive than I’d remembered, she had a low-grade fever, and the clincher…she howled when I palpated her abdomen.
Damn! Possibly the worst day of the year for abdominal pain.
X-rays showed a significant amount of gas in her intestines. But further evaluation and a definitive diagnosis were not likely to happen in my hospital. Not when one hour remained before the staff cleared out for the holiday. Not when any bloodwork would be unlikely to get turned around by the lab until after Christmas.
To make matters worse, the specialty hospital across the street had sent out a notice indicating a communal specialist vacation. No surgeons or internists until Monday? Sorry, Trixie, you’re traveling.
At the Animal Medical Center in Cooper City, Florida, a board-certified emergency doc was holding down the fort. That was more than good enough for me. There, Trixie could get an ultrasound along with an evaluation by a specialist ideally trained to handle “acute abdomens” (that’s what we call painful bellies with no clear diagnosis).
By the time she arrived, however, Trixie’s belly and fever had relaxed. The ultrasound was negative…nothing interesting or diagnostic revealed itself. Her osteoarthritis and seemed the worst of it, according to the ER specialist. So he hooked her up with corticosteroids and opiates and sent her home for the holiday.
Though most of the extensive labwork had revealed nothing of interest, her platelet count was significantly lower than it should have been. Although her owner swore up and down that he’d never seen a tick on her, the ER doc had tested for tick borne disease anyway. Negative.
But Trixie’s condition worsened over the next 24 hours. Though Trixie’s platelet count had gone up in this time (almost certainly the work of the steroids), her overall condition was worse than ever. Her restlessness had disappeared with the heavy doses of pain medication, but now she could hardly stand and her fever was back.
So you know, a painful dog with a fever and low platelets pretty much screams out to be tested for the wily bacteria spread by ticks. But these bugs have a way of hiding inside cells as they do their dirty work. It makes tham hard to find on some tests. That’s why I re-tested her with a more specific test (despite her owner’s protests over Trixie’s ticklessness).
Here's a pic of the ehrlichia organism hiding in a white blood cell:
And guess what? She was positive for an early case of Ehrlichiosis, one of a wide variety of potentially fatal tick-borne diseases and the one we see most commonly in South Florida.
That’s when we started giving her big doses of Doxycycline, a tetracycline-like antibiotic with a high rate of efficacy against these difficult-to-reach bacteria. Within 24 hours she’d improved enough that we could taper down her dose of steroids and pain medications. And after the weekend (three days later) she’d finally reached a pre-crisis state of relative comfort.
But Trixie’s not out of the woods yet. Her discomfort may have abated. Her platelet count may be normal. Her fever may have subsided. But she’ll remain on Doxycycline for at least a month. And the long-term effects of Ehrlichiosis are yet to be determined. That’s because some dogs respond beautifully to treatment while others do so only to relapse later with the “chronic form” of the disease. (Read more about the different forms of ehrlichiosis here.)
Most tick-borne diseases have a way of working insidiously. Not only are they hard to diagnose in cases like Trixie’s, they’re often hard to treat, too. Sometimes dogs will present with symptoms even more non-specific than Trixie’s. Sometimes the platelets will be normal and no pain or fever will be evident. Sometimes they just seem tired, leaving us to work them up for cardiac disease, thyroid malfunction and other red herrings.
And sometimes, as in Trixie’s case, they’ll come up negative on the ER doc’s SNAP test, too (this test looks for antibodies against Ehrlichia canis, one of several varieties of the organism). If the dog is tested very early on in the process the antibodies may not be present yet. And if the organism doesn’t exactly conform to the standard Ehrlichia canis bug but to another less common version of ehrlichia then it’s possible that no standard blood test will ever prove the presence of this bacteria.
Luckily, we have a new test for ehrlichia that’s closer to foolproof than any of the SNAPs and antibody titer measuring tests. It’s called PCR and it looks for minute quantities of the bacteria’s DNA in a blood sample. Trixie’s was positive. So was her antibody titer just one day after the ER’s SNAP.
The same can be true for humans who suffer Lyme and other tick-borne diseases (yes, humans can get ehrlichiosis, too, though not from their dogs). Varied symptoms like chronic fatigue, transient joint pain, flu-like symptoms and even nervous system effects can make diagnosis difficult in humans. In fact, I had one friend whose Lyme disease was first diagnosed as multiple sclerosis (!) before one smart, second-opinion neurologist caught the infection.
In Trixie’s case the confounding element was her historical lack of ticks. But we all know that just one tick has the capacity to spread disease. So here’s the message in this good news case:
Whether your dog gets ticks or not, whether you’ve actually seen a tick or not, whether your dog has obvious symptoms or not, tick disease IS possible. Letting your vet work up a suspicious finding as seemingly innocuous as a slight drop in her normal platelet level is always a good idea.
There may be a lot about tick-borne diseases we don’t understand. But one thing this South Floridian does know is that her dogs will keep getting tick meds…whether I see a tick or not.
PS: Here are the ticks that carry ehrlichia. The first is the "lone star" tick. The second is the brown dog tick.