Spotlight on Lyme disease

Spotlight on Lyme disease

Dr. Susan E. Little address epidemiology, treatment of this tick-borne disease
May 01, 2011

Dr. Susan
Editor's Note: Susan E. Little, DVM, PhD, Dipl. EVPC, holds the Krull-Ewing Endowed Chair in Veterinary Parasitology at the Department of Veterinary Pathobiology, Center for Veterinary Health Sciences at Oklahoma State University. From 2008 to 2009, she served as the president of the American Association of Veterinary Parasitologists. She has written more than 100 articles on veterinary and human parasites and tick-borne disease agents. And she has been awarded two Excellence in Teaching Awards from the national Student American Veterinary Medical Association.

DVM: Is Lyme disease increasing?

Tick troubles: Cases of Lyme disease are cropping up in more and more areas across the United States. Remember: High deer numbers mean high tick numbers.(COMSTOCK/GETTY IMAGES)
Little: We don't know because we don't have a reporting system similar to that used in humans to track the numbers. But cases in people are increasing, so if we use the humans as a sentinel of canine disease, then we would expect that the numbers of infected dogs are increasing. And areas of transmission also appear to be increasing as the maintenance cycles slowly spread into areas where Lyme borreliosis wasn't previously endemic. In people, the case reports are coming from a larger number of counties and states than in previous years. The focus remains the same, with the majority of cases from the Northeast and upper Midwest and a few from the West Coast. But in recent years, we've seen more cases cropping up around the Great Lakes area and down the East Coast to as far south as North Carolina, but no laboratory-confirmed reports of infections have been seen yet in the deep South.

DVM: Is there any new information or new findings about Lyme disease that veterinarians should know about?

Little: Well, certainly awareness of spread is important, especially if you are practicing in an area where transmission has only recently been recognized. Practice protocols may need to be updated with a renewed emphasis on tick control and perhaps periodic reconsideration about recommendations for vaccination. But I think it is also important that veterinarians remain aware of the prevalence of coinfection from other pathogens in dogs that test positive for Borrelia burgdorferi antibodies. We can't afford to stop looking for or considering coinfections once we make that initial diagnosis of a single tick-borne illness, like Lyme disease. If an animal has one tick-related infection, it may well have others. Coinfection should be particularly suspected when a patient fails to respond as expected to treatment for a single diagnosis.

DVM: Other than dogs, which other animals are most likely to contract Lyme disease?

Little: Horses are often infected in endemic areas, and recent case reports suggest this infection can cause neurologic disease and other clinical disease in some horses. As with dogs, not every animal infected will develop clinical Lyme disease. Antibodies to B. burgdorferi have also been reported in cats and cattle, but we don't have clear evidence of clinical disease associated with the infection.

DVM: I've read it's white-tailed deer and white-footed mice that are the primary maintenance hosts for the deer tick and the primary reservoirs for the B. burgdorferi infection. Is that still accurate?

Little: The white-tailed deer is the cornerstone species that supports the tick populations and, thus, allows transmission of Lyme borreliosis. Adult black-legged ticks thrive when deer are present, and since this is the reproductive stage, high deer numbers mean high tick numbers. The immature ticks feed on and acquire B. burgdorferi from rodents, but some recent data shows that other small mammals, like shrews and chipmunks, are just as important or even more important reservoir hosts in some regions.