With the increasing use of the Snap 3DX test in healthy animals, more questions than answers are being generated. What further testing should be done with a positive test? Who should be treated? There seem to be as many answers as there are people to ask.

The reality may be that there is no correct answer given the state of present knowledge about Borrelia burgdorferi and Ehrlichia canis. In a very crude survey of veterinarians throughout the state, there seems to be a higher prevalence of Lyme positive the further north you go in the state, and more E. canis positive the further south. A three doctor practice in Lynchburg has a consistent 15% positive on the Ehrlichia portion of the 3DX test and a 3% positive on the Lyme portion when used for routine screening with the annual heartworm test. In order to assist in making logical decisions about the correct next step after a positive E. canis test, Dr. Ed Breitschwerdt, head of the N.C. State College of Veterinary Medicine Vector Borne Disease Diagnostic Lab was contacted. Information regarding Lyme disease was obtained through a personal communication with the Animal Health Diagnostic Lab at Cornell.

"Healthy E. canis positive 3DX

What the test detects: Antibodies to E. canis and E. chaffeensis. Does not detect E. ewingi antibodies. As with any screening test, there may be false positives.

What to do after positive test: If the dog is otherwise healthy, Dr. Breitschwerdt recommends performing a CBC. If the dog is anemic, neutropenic, thrombocytopenic, or hyperglobulinemic, treat with doxycycline at 5mg/kg BID for 21 days. If CBC results are normal, treatment may not be indicated. Alternatively, a 3DX positive for ehrlichia can be confirmed by IFA testing and by PCR testing. If a healthy dog is PCR positive, the dog is actively infected and treatment is indicated.

Healthy Borrelia burgdorferi positive 3DX

What the test detects: Antibodies against the C-6 peptide, which is highly specific for B. burgdorferi. False positives, especially when whole blood is used, are expected. Cornell Diagnostic Lab estimates a 6% false positive rate. They recommend using serum or plasma for the test.

What to do after positive test: Once infected with Borrelia burgdorferi, a dog will likely be infected for life. Most dogs will never show signs. If a dog is positive that was previously negative, treatment may be indicated, but in an asymptomatic dog treatment will not cure the infection. Certainly, in symptomatic dogs, treatment improves clinical signs quickly. Although treating healthy 3DX positive dogs may not be indicated, Cornell Lab strongly recommends treating healthy positive dogs that are placed on corticosteroids for any reason. They recommend using doxycycline at 10mg/kg BID for 21-28 days when the decision to treat is made.

In Summary

The science of vector borne disease diagnostics and treatment is evolving. Accurate, easily retrievable patient records when using the Snap 3DX as a screening test will be a big asset as new information changes our decisions about what to do with a positive test.