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Prevalence of CVBDs

DR. JOE HOSTETLER: The first question to address is, Are we seeing an increase or a spread in the geographic distribution of canine vector-borne diseases in the United States? Or are we just looking for these diseases in areas where we haven’t historically looked?

DR. THOMAS MATHER: I think we are seeing an increase. The good news is that we’re seeing fewer dog tick-transmitted infections in much of the United States. That’s largely because of successful use of preventive products in pets. However, the big difference we are seeing now is due to the tremendous increase in deer ticks, or black-legged ticks, in much of the Eastern United States, especially the mid-Atlantic states, the upper Midwest, and New England.

DR. EDWARD BREITSCHWERDT: Like most complex issues in life, the increase is multifactorial. There’s clearly been an increase in the incidence of tick-borne diseases related to changes in our society. People often are now frowned upon if they hunt deer. In certain communities, deer are protected, allowed to reproduce unabated. Deer are a tremendous blood reservoir for ticks, so the tick populations have increased. Also, many more people have moved out of cities and into rural environments where their contact with ticks is much more frequent. Another factor is that we’ve identified new tick-borne diseases or disease-causing agents, and we’ve come up with better diagnostic tests to help veterinarians confirm the presence of tick-borne diseases in their patients.

DR. LEIF LORENTZEN: Testing is a big part of it. With the diagnostics practitioners have in their practices today, it’s easier for them to determine what is in their practice population. We’re very good now at monitoring what’s in an area. Following the ebbs and flows of these diseases is more challenging. I think we will begin to see more research tracking the movement of these diseases with ticks. We published some information in Veterinary Parasitology in 2009 with Drs. Susan Little and Dwight Bowman showing that prevalence is very regional and state specific.1 In the Northeast, you see more anaplasmosis and borreliosis. In some areas of the Northeast, we are seeing that as much as 3% to 4% of animals are serologically positive for Borrelia and Anaplasma species. Likewise in the Southeast, you can see animals that are serologically positive for Ehrlichia and Anaplasma species.

DR. HOSTETLER: Are these diseases moving out of an area, or are they just moving into new areas?

DR. MATHER: When I first came to Rhode Island in 1993, people were getting Lyme disease in the southern part of the state. We started surveillance across the entire state looking for deer ticks and didn’t find them in almost half the state. That has changed now. If you look at our earliest years’ data, about 275,000 Rhode Islanders might have encountered a deer tick where they lived. By 2006, that number had increased to about 720,000—almost three-quarters of our state’s population. Even in a place that’s less than 40 miles north to south, we’ve seen changes in the distribution of ticks. That’s a big factor.