Visiting Veterinarian : No quick answers
Keaton, a four-year-old golden retriever, arrived at my office one spring day for a sudden onset of lethargy and lack of appetite. The only abnormality on physical examination was a whopping fever of 104. Twenty-five years ago, these cases were easy. "Your dog has Rocky Mountain Spotted Fever," I would pronounce, then equivocate slightly: "Either that, or Lyme disease."
The explanations were not too time-consuming, treatment not too expensive. We had no in-house tests for tick-borne diseases and virtually everyone declined send-out tests to veterinary reference labs. I would give a few injections, then send owners home with a vial of pills, assuring them their pups would be right as rain in a few days - and most were.
Nowadays, we know so much more about tick-borne diseases and have a wider array of diagnostic options, which is great except all these medical advances are making my job way complicated.
"Your dog probably has one of the tick-borne diseases," I told Keaton's owner. "Could be Lyme, Anaplasmosis, or Rocky Mountain Spotted Fever." I flipped back through Keaton's record.
Bear with me. This is where it gets confusing. For eight years now, we have had the 3DX test we can run quickly right in the office. It screens for antibodies to Borrelia burgdorferi, the organism that causes Lyme, to Ehrlichia canis, which we rarely see on the Vineyard except in dogs that contracted it elsewhere, and to heartworm. A positive test does not necessarily mean a dog is currently infected. It means he has been exposed to the organism and his body has responded by making antibodies. The test is not affected by vaccination nor does it indicate immunity against reinfection. Keaton first tested 3DX Lyme positive three years ago, at which time we treated with antibiotics.
Not unusually, Keaton continued to test positive in subsequent years. His owner followed up with the Lyme Quantitative C6 titer, a send-out test that became available in 2005, which helps differentiate between exposure and infection. Keaton's QC6 supported the conclusion that he had persistent antibodies, not active Lyme infection.
But wait. There's more. In 2007, the 4DX test became available. It screens for antibodies to one additional tick-borne disease caused by Anaplasma phagocytophilum, an organism that used to be called Ehrlichia equi, until scientists reclassified and renamed it a few years back. Keaton first tested Anaplasma positive during a routine screen at his 2008 annual physical. His diligent owner once again approved further tests, this time one called an Ehrlichia PCR, which confirmed that Keaton, like many other Vineyard dogs, had persistent antibodies, but was not currently infected - which brings us to his visit in May 2009, when he is one sick puppy.
"It's probably Rocky Mountain Spotted Fever," I began, "or it could be Lyme, or Anaplasmosis. We'll do the 4DX test right here, but since he's been testing positive for years, that may not help much."