Visiting Vet: Tickborne diseases

They can be as complicated to diagnose for dogs as for humans.


Last week I saw three lovely dogs, Tulip, Daffodil, and Hyacinth. Tulip and Daffodil were here for annual physical exams, vaccinations, and preventive healthcare. Hyacinth came in because she wasn’t feeling well. We drew blood and ran a test called an Idexx 4DX SNAP on all three dogs. This handy little test identifies antibodies to three tickborne diseases, anaplasmosis, ehrlichiosis, and Lyme, and also canine heartworm antigen. No time today for a lesson in immunology. Suffice it to say that antibodies are the body’s immune response to a pathogen, while antigens are any foreign substances that trigger an immune response. The important point for today is that the anaplasma part of the 4DX test looks for antibodies, not antigen.

Why do we care? Because all three dogs tested positive for anaplasma antibodies, and it meant something different in each case.

What is anaplasma, anyway? It’s a type of bacteria. The 4DX tests for antibodies to two different anaplasma species, both of which are carried by ticks, and can cause serious illness. Welcome to Martha’s Vineyard. Today we are focusing on “granulocytic anaplasmosis,” caused by Anaplasma phagocytophilum. This organism is usually carried by our old friend the deer tick, and can infect dogs, cats, horses, cattle, small ruminants, wildlife, and humans. Signs in dogs usually include fever, lethargy, loss of appetite, and sometimes lameness. Occasionally they may also have vomiting, diarrhea, and/or respiratory symptoms.

Our next question is whether Tulip and Daffodil are truly infected with the anaplasma organism. Here’s where it gets confusing. It is perfectly possible these two pups were exposed to anaplasma sometime in the past, but their immune systems fought off the disease, making antibodies that are now showing up as a positive anaplasma test (AP+). These dogs do not seem sick. So do we just ignore it? The answer depends on many factors. Every veterinarian has their own approach. For me, if this is the first time Tulip and Daffodil are testing AP+, and if they have absolutely no symptoms of illness, I recommend one or two follow-up tests.

Hang in with me now. The big fancy test is a PCR test that looks for antigen from the anaplasma organism in the blood. In other words, a positive PCR test indicates that Tulip or Daffodil are currently infected with the bacteria. But the PCR test is expensive, results can take a while, and false negatives do occur. The second option is a complete blood count (CBC). This looks at the pups’ red blood cells, white blood cells, and thrombocytes (also known as platelets.) A CBC is more affordable, and we can usually do it right in my office in an hour or two. Most specialists agree if the CBC is normal in an otherwise asymptomatic animal (one who doesn’t seem sick), the dog is unlikely to have an active infection. The main abnormality we look for is a low platelet count, technically called thrombocytopenia. Once a dog has tested AP+ once, they often remain positive for years, as their immune systems often continue to produce antibodies. So after the first time, I don’t worry about it if the dog seems healthy otherwise.

So here are our three dogs. Hyacinth is sick. She has a low-grade fever. She is not eating well, and seems really down and out. Tulip and Daffodil are fine. All three are AP+ for the first time in their lives. We do a CBC on all of them. Tulip’s CBC is normal. I called her owner and advised them to keep an eye on her for any illness in the future. The incubation period for anaplasmosis is usually only one to two weeks from the tick bite, so as long as Tulip continues to look healthy, we are done. Daffodil’s CBC, however, showed a mild thrombocytopenia. I called her owner: “We could send out the PCR test to try and confirm, but in any case, I would like to treat her, to be on the safe side.” The big lab confirmed our finding of thrombocytopenia, and while we are waiting for the PCR results, we started Daffodil on doxycycline, the treatment of choice for anaplasmosis.

Hyacinth is another story. Her CBC showed an elevated white blood cell count and significant thrombocytopenia. Thrombocytes are responsible for helping blood clot, and Hyacinth’s count was low enough I was concerned. I examined her inch by inch, looking for signs of bleeding. Her gums were pink. No bruising visible anywhere. No blood in her stool or urine. No nosebleeds. Her lungs sounded fine. I sent her home on doxycycline and pain medication with instructions to keep her quiet and a plan to recheck in three days.

But the next morning Hyacinth was worse. She was dizzy, weak, uncoordinated, and depressed. “I think you should take her off to a specialty facility where they can run more tests, hospitalize her, even give a blood transfusion if needed,” I told her owner. I called Cape Cod Veterinary Specialists to refer Hyacinth. “I’m worried I’m missing something,” I told the ER doc. “I’ve seen a lot of anaplasmosis cases, but they’re usually not this sick.” The ER doc interrupted me to say that this spring they had already seen multiple cases of anaplasmosis that were so severe the dogs required several days of hospitalization.

They admitted Hyacinth for in-patient treatment, including intravenous antibiotics, and additional testing, but later transferred her to yet another facility to be evaluated by a neurologist. As of Friday, she seemed to be improving a bit. They found a blood clot in her heart, and we do not have a definitive diagnosis, but anaplasmosis is still on the differential, as is another tick-borne disease we see here, Rocky Mountain Spotted Fever. Welcome to Martha’s Vineyard. Please, use a good flea and tick product on your pets. Check them over carefully by hand for ticks. Every day. Call your veterinarian at the first sign of any illness. And keep your fingers crossed for Hyacinth.