VBD Screening: 3 Steps to Take When "Healthy" Pets Test Positive
While it can be challenging when a healthy dog tests positive for one or more vector-borne diseases, there are guidelines available to help you give the most up-to-date recommendations to your clients.
1. Review the Accuracy of the Test
When an apparently healthy dog tests positive for a vector-borne disease, the first step is determining if the test is accurate. Confirm the correct sample from the correct patient was submitted, and don't hesitate to repeat a test if there is any question.
For each different vector-borne pathogen, there may be multiple tests available for screening and diagnosis. Each diagnostic lab that has a test available should also have information on the sensitivity and specificity of the test, and for B. burgdorferi there should also be information on whether previous vaccinations affect the test result.
As with any diagnostic test you select, you should confirm the sensitivity and specificity with the provider, and understand how to interpret a positive or negative result. Ultimately, if you get back a result that doesn't make sense, or you want to confirm a result that seems surprising, it's best to repeat testing on a new blood sample, and to use a different test (if viable alternatives are available). You can also always reach out to an expert for advice.
2. Evaluate for Clinical Signs and Lab Abnormalities
Once you've confirmed your result, you should determine whether the dog is truly asymptomatic.
Some manifestations of vector-borne diseases are subtle, or are only found on lab work. As such, a physical exam and minimum database (CBC, chemistry panel, and urinalysis) are the most important follow-up tests after a positive vector-borne disease test. It is also important to determine if the positive test is the result of a new exposure; antibodies against many vector-borne diseases can remain present for months or even years after exposure. Ask clients about flea and tick prevention and whether they've seen fleas or ticks on their dog; annual vector-borne disease testing can also play an important role, since it will give you at least one point in time each year to compare.
3. Determine Whether or Not to Treat
The decision of whether or not to recommend treatment for a vector-borne disease will be based not only on the results of a screening test for vector-borne disease, but also your interpretation of the entire clinical picture including the pet owner's perspective. There aren't strict guidelines for the treatment of most vector-borne diseases due to a paucity of evidence. However, the American College of Veterinary Internal Medicine updated their guidelines for the management of asymptomatic dogs with positive B. burgdorferi antibody tests. Unfortunately, the decision of whether to treat Lyme-positive dogs who appear healthy with no proteinuria or bloodwork abnormalities remains controversial.
In addition to discussing treatment options, you should take the opportunity to reevaluate the flea and tick prevention strategies used and recommend improved flea and tick prevention. Regardless of the disease outcome, finding antibodies against a vector-borne disease in a dog means that dog has certainly been bitten by an infected tick, and care should be taken to prevent ongoing exposure in the future.
Vaccinations are not available against most vector-borne diseases, with the exception of B. burgdorferi. After screening for subclinical illness, particularly proteinuria, you should consider vaccination against Lyme disease for all truly asymptomatic dogs with antibodies, since no natural immunity occurs from prior infection. The evidence for any negative side effects from the Lyme vaccine, even in seroreactive dogs, remains anecdotal at best, and there are no known negative impacts of post-vaccinal Lyme-specific circulating immune complexes, which increase only transiently after vaccination.
Looking Ahead for Better Vector-Borne Disease Management
Because of the difficulty researchers have had using experimental models for vector-borne diseases in dogs, and even studying these diseases in naturally infected populations, there are a lot of questions about the optimal management of vector-borne disease in dogs. Remember that commercial veterinary diagnostic labs have support staff, including board-certified specialists, who are available to answer questions about their diagnostic tests, interpretation of test results, and even patient management. Tools for clinical decision support are also increasingly available through some veterinary software applications. As part of their educational mission, most university veterinary teaching hospitals also provide consultations to primary care veterinarians at no cost.
While it can be difficult to know how to proceed when a seemingly healthy dog tests positive for a vector-borne disease, there is consensus among veterinary infectious disease experts that test results should be confirmed, dogs should be screened for subclinical abnormalities, and these are good opportunities to encourage year-round flea, tick, and heartworm control. Further research on the effects of vector-borne diseases in both dogs and people will hopefully begin to clarify some of the ongoing controversy associated with these common illnesses.