A happy, high-energy 5-year-old Labrador retriever presents to you for a wellness exam and you notice a small Ixodes species tick on the back of its neck. You remove the tick, perform a physical exam, give vaccines and run an in-clinic vector-borne disease screen as part of yearly wellness testing. The test comes back positive for Lyme disease. The dog, which used to live in Minnesota, is bouncing off the wall. You inform the owner of the results, and the owner tells you her son was diagnosed with Lyme disease. What do you do?
Where Fetch dvm360 educator and VETgirl co-founder Garret Pachtinger, VMD, DACVECC, lives and works—Veterinary Specialty and Emergency Center in Levittown, Pennsylvania—40 to 60 percent of dogs test positive for Lyme disease. Of those positive dogs, 95 percent are subjectively judged to be completely asymptomatic.
But what is asymptomatic, really? Dr. Pachtinger asks. Is it what we veterinarians perceive as asymptomatic, or what the client perceives? What about what the dog thinks? What if this is a happy Lab that would wag his tail even with a broken femur? Can we really judge this patient to be asymptomatic?
A twist on a classic story
The classic clinical signs of Lyme disease in dogs include shifting leg or transient lameness, a low-grade fever and anorexia in acute disease, Dr. Pachtinger says. Development of fulminant glomerular nephropathy is possible and carries a poor prognosis. Labrador and golden retrievers seem to be predisposed to renal disease associated with Lyme. Neurological and cardiac manifestations are quite uncommon in small animal patients.
While you still want to run a complete blood count (CBC) and serum chemistry profile in dogs you suspect of having Lyme disease, Dr. Pachtinger says these lab tests will not give you the smoking gun answer except in cases with Lyme nephritis.
Remember: an Ixodes species tick must be attached for at least 48 hours to transmit disease. If the tick is not engorged, Dr. Pachtinger says the likelihood of disease transmission is very small.
Risk factors for Lyme disease include:
The presence of an engorged Ixodes species tick on a dog
A dog that lives or visits an area endemic for Lyme disease (use the CAPC map to find out Lyme prevalence rates in the United States and Canada)
A positive result on an in-clinic vector-borne disease screen such as IDEXX’s 4DX SNAP test
Clinical signs correlated with Lyme disease.
The 4DX test takes three to five weeks after exposure to indicate seroconversion in dogs. If clients notice an engorged tick and want to test the dog, advise them to wait four to six weeks. If they won’t wait, tell them you can test today, but you’ll be testing for possible previous exposure, not for the tick that was just removed, says Dr. Pachtinger. An additional confounding factor with the 4DX is that the assay will stay positive for a long time (think years) even after successful treatment.
Dr. Pachtinger asks clients if their dog has tested positive for Lyme disease before running the test and warns them that the value of the results will be questionable if the patient has tested positive in the past. A positive blue dot on asymptomatic dogs raises an important question—should we be screening asymptomatic dogs for Lyme disease at all?
There are pros and cons to screening the general population for Lyme, Dr. Pachtinger says. The advantages include providing seroprevalence data, providing information for human health risks and helping to diagnose Lyme disease in patients that have clinical signs, azotemia or protein-losing disease. The disadvantages include false positive results that lead to unnecessary owner distress and expense, overtreatment and development of resistance.
Dr. Pachtinger says that in endemic areas, it’s important to screen for Lyme disease, but just because you get a positive result doesn’t mean you should start treatment. He personally does not treat asymptomatic patients with a positive Lyme disease result on 4DX.
So, about treatment ... Turn to the next page for the details.
Doxy to the rescue
If a patient does display clinical signs, doxycycline is the most efficacious choice for treatment. Dr. Pachtinger’s recommendation is to give 10 mg/kg orally once daily in the morning for four weeks. Four weeks of treatment have been recommended because the clinical manifestations of disease resemble those of late-stage disease in human patients, for which relapses occur when treatment durations of less than 30 days are used. Clinical signs should be completely resolved within two to three days. Dr. Pachtinger does not administer analgesia (e.g. NSAIDs or tramadol) at the same time as starting doxycycline—he thinks that if you do, you can’t definitively determine which drug is making the dog feel better.
Doxycycline is not without risks, Dr. Pachtinger reminds us—it can increase the likelihood of esophageal stricture. This is not a medication that owners should give with a treat after dinner right before going to bed, and it’s important to counsel owners accordingly. Patients need to be up and moving for several hours after giving the drug. His recommendation? Give it at breakfast. Other drugs to consider include amoxicillin, cefovecin sodium, ceftriaxone and azithromycin, which have all be shown to be effective.
In human medicine, it’s common to give a single dose of doxycycline at the time of the bite to prevent Lyme disease. In people, Lyme disease is usually caught much earlier because of the "bull’s-eye" erythema migrans rash seen on the skin. Typically, the disease is not caught early enough in pets for a single dose to be effective, Dr. Pachtinger says. And even if it were, a single dose of doxycycline has not been shown to prevent Lyme disease in dogs.
Keeping an eye on Lyme
Monitoring, as you may have already guessed, is a challenge. The C6 quantitative Lyme test has questionable clinical value, says Dr. Pachtinger. And patients may have a positive result on a 4DX for years. Currently, the best way to monitor patients with Lyme disease is resolution of clinical signs, Dr. Pachtinger says.
Remember the Lyme-positive Labrador that was bouncing off the walls from the beginning of this article? What would you do?
Give one dose of doxycycline
Prescribe four weeks of doxycycline
Do a urine dipstick and look for evidence of proteinuria.
Turn the page to see if you're right ...
If you answered C, you’re spot on!
No proteinuria = no treatment. If there is evidence of proteinuria (for example, 3+ protein on 1.025 urine specific gravity), then Dr. Pachtinger would consider performing a urine protein:creatinine ratio and consider sending the dog home on four weeks of doxycycline. He recommends a recheck exam and urine dipstick in three months for follow-up. If there is a high C6 quant test, recheck in six months. Do not repeat the 4DX as a follow-up for Lyme disease.
What if the C6 doesn’t decrease after six months? Does that mean you have treatment failure? Reexposure? It’s hard to know, Dr. Pachtinger says, which is why this test is not definitive. We’re back to using resolution of clinical signs as the best indicator of treatment success.
If you have a patient with acute-onset hindlimb lameness and the owner removes occasional ticks from the dog in a Lyme-endemic area, Dr. Pachtinger still recommends checking a urinalysis and treating if the dog is positive for proteinuria. A full workup including a CBC and serum chemistry profile, plus radiographs is also recommended. If the dipstick is negative for proteinuria, then counsel the owner on treatment, making sure to go over risks. If the owner elects to treat, remember: If the lameness isn’t 100 percent improved in two to three days, then it isn’t Lyme disease. Also remember that treatment does not completely clear spirochetes from the blood.
If you send an engorged tick out for testing and it comes back positive, should you treat the dog? Dr. Pachtinger says that, academically, he still wouldn’t treat asymptomatic dogs because doxycycline won’t clear the infection or reduce the risk of them developing clinical signs.
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What about a Lyme vaccine? Dr. Pachtinger says it doesn’t make sense to vaccinate pets that are Lyme positive, though there’s a lot of controversy over what the best protocol is. In addition, testing should not be affected by vaccination, according to Lyme vaccine manufacturers. The best prevention for Lyme disease in seropositive patients is aggressive tick prevention. Time for your ever-favorite tick-preventive talk!