Spotlight on Lyme disease - DVM
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Spotlight on Lyme disease
Dr. Susan E. Little address epidemiology, treatment of this tick-borne disease


DVM360 MAGAZINE


DVM: We know the initial signs in people include the characteristic skin rash and flu-like symptoms. Are the signs the same in animals? What should animal owners and veterinarians be looking for?

Little: Dogs don't develop that characteristic rash of erythema migrans. In fact, in most cases dogs don't develop much illness from acute infection at all. So we often don't see dogs with Lyme disease until several months after exposure, once the arthritis or other condition from long-term, established infection has developed. The classic presentation is an otherwise healthy dog with recent onset of polyarthritis that may migrate, resulting in a shifting leg lameness, and without any other explanation such as trauma.

DVM: Doesn't that make it hard to diagnose in older dogs then?

Little: Yes, it can present a challenge. We diagnose by testing for specific antibodies to B. burgdorferi, but it is widely thought that the majority, perhaps as many as 95 percent, of dogs that test positive for the antibodies won't develop disease. Those that do are likely to develop chronic or recurrent polyarthritis, but a minority may develop the more severe renal nephritis or Lyme glomerulonephritis, which is potentially fatal.

DVM: Is serologic testing helpful, or is it often nonspecific in diagnosis?

Little: In clinical situations in which you have signs of disease and a suspected diagnosis, serology can help confirm the diagnosis of Lyme disease. We also have access to a quantitative C6 assay that can determine the level of antibodies present and help the veterinarian decide if there is an active, ongoing infection. The quantitative C6 test can also be used to monitor response to treatment. Because so many dogs in endemic areas have antibodies to B. burgdorferi, there can be a tendency to overdiagnose the disease. But if a dog has the characteristic signs, has antibodies at a level consistent with active or recent infection and responds to treatment, that certainly supports the clinical diagnosis.

DVM: What is the treatment of choice?

Little: Doxycycline is the treatment of choice. Other antibiotics, such as penicillin, are also effective, but those won't treat the rickettsial coinfections we often see with B. burgdorferi infection, such as ehrlichiosis or anaplasmosis.

DVM: In an animal not diagnosed and treated, what are the long-term effects of infection?

Little: As I noted, most dogs that are infected do not go on to develop disease, which is why it is recommended that veterinarians not routinely treat a healthy dog based on the presence of antibodies alone. Some veterinarians may decide to treat a recently infected dog—a dog that had previously tested negative—to try to prevent the illness that can be associated with allowing an infection to persist, but repeated treatments to clear antibodies from a dog that does not have any clinical disease are not indicated.

DVM: Any new and promising vaccinations or acaricides in development?

Little: On the market now are several effective vaccines for Lyme disease. As for acaricides, K9 Advantix II (Bayer) has a label change from its previous version that states the product can be used as always, applied once monthly, but that it also can be used as often as weekly in dogs. More frequent application of acaricides is occasionally indicated when dogs are exposed to overwhelming or extreme environmental tick infestations. Effective acaricides for our equine patients is a tougher problem, as horses tend to sweat and shed the chemicals, so the acaricides don't have the duration we would like in horses.

DVM: Are there any myths in the veterinary field about the disease that you'd like to dispel?

Little: Actually, to their great credit, most veterinarians I talk with today are educated and informed about Lyme disease. We are still troubled by all the things we don't know and don't understand, but it isn't so much myth as the need for more research to clarify certain issues. I am occasionally asked about the significance of a positive C6 test result, the antigen on the 3DX or 4DX Snap (IDEXX), in a vaccinated dog. Vaccination will not cause the test to become positive—only active or recent infection does that—but since the vaccines we have are not 100 percent effective at preventing infection, occasionally vaccinated dogs that are then exposed to ticks will test positive.


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Source: DVM360 MAGAZINE,
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