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Diagnosing CVBDs

DR. HOSTETLER: What is the best way for veterinary clinicians to approach diagnosis of canine vector-borne diseases?

DR. LORENTZEN: We have very accurate, cost-effective ways to test animals for these diseases. Peptide technology allows us to produce cost-effective assays with high sensitivity and specificity for the pathogens. That gives practitioners a powerful tool in the clinic. In the United States, the standard of care is regular heartworm testing. It is now easy to add tests for other vector-borne diseases as well. Screening an animal on an annual basis for exposure to these infections can direct veterinarians to recommend further workup or preventive care. Furthermore, veterinarians can determine how common an organism is in their area and how vigilant they should be about recommending their patients be on a preventive.

DR. BREITSCHWERDT: The other advance that has helped us in regard to canine vector-borne diseases is the use of molecular diagnostic tests. All the major veterinary diagnostic companies have introduced these tests in recent years, so they’re available to veterinarians. They allow us to identify a DNA fingerprint to confirm that an animal has not only been exposed, but is actively infected. IDEXX Laboratories has done a nice job of trying to separate out the screening tests from confirmatory diagnostic tests and helping veterinarians to understand that if a screening test comes up positive, there are a few more steps to a definitive diagnosis. Doing a blood count to ensure that the dog’s not anemic, thrombocytopenic, or hyperglobulinemic is one step along the way, and molecular diagnostic testing can be another important component for confirming infection.

DR. LORENTZEN: Practitioners who are routinely looking for and thinking about vector-borne diseases know what’s in their area, and CVBDs are higher on their list of differentials when animals come in with clinical signs consistent with those infections. In those situations, you really need the combination of the two tests because in the early stages of an infection PCR is very sensitive and obviously very specific for infection. But as that infection matures, a lot of these organisms—especially the Rickettsia organism—will move out of the circulation and the sensitivity of PCR will decline. That’s when you start seeing seroconversion and the antibodies are detectable in the blood.

DR. BREITSCHWERDT: When veterinarians use the testing that’s available, they can make a diagnosis and treat the dog with an appropriate therapy, and the dog gets better. But with cases that don’t respond completely, look for another canine vector-borne disease. For example, doxycycline has been the most widely used antibiotic for the treatment of infection with many of these organisms because it’s highly effective. But doxycycline is not effective in clearing Babesia organisms. If the dog is co-infected with Ehrlichia and Babesia organisms it might get better on doxycycline. But once you stop the antibiotic, the dog relapses because the Babesia organism is still present. That’s also true of co-infections with Bartonella species. I’ve come to the conclusion over the last couple of years that you just cannot give a dog enough doxycycline to eliminate that infection. If we are unsuccessful in treating the infection, remember that co-infections are common. If the animal fails therapy, look for another organism or another disease.

DR. MATHER: To make a difference, people need to be able to identify ticks. They need to be able to tell the difference between dog ticks and deer ticks and lone star ticks because each transmits different pathogens. The very first thing to know is that all ticks come in small, medium, and large sizes, so you need to look more closely. Picking up a few basic skills can be really helpful in not only a diagnosis, but in focusing on prevention as well.

DR. BREITSCHWERDT: One way to do that is to have a techncian in the practice trained in tick identification. Several companies, including Bayer, have produced tools for tick identification that can be kept in the clinic. If a tick is brought in that can’t be identified, send it to an entomologist. I don’t expect veterinarians to become tick experts because they don’t treat ticks. But on the other hand, being able to identify ticks is important to their patients.

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