Tick-borne diseases march into all 50 states, survey says

Orlando, Fla — A new survey shows that tick populations are not only increasing in number but tick-borne diseases are showing up in every state in the country.

The results, first presented during the 2008 North American Veterinary Conference (NAVC), were part of a voluntary national veterinary reporting system that was developed by IDEXX Laboratories of Westbrook, Maine.

Dr. Susan Little, a veterinary parasitologist at the Oklahoma State University's Center for Veterinary Health, reports that at least three tick-borne diseases, Lyme disease (Borrelia burgdorferi), anaplasmosis (Anaplasma phagocytophilum) and ehrlichiosis (E.canis) have been reported in every state in the country. The conclusions come from an analysis of 3 million data points gathered by IDEXX Laboratories from 2001 to mid-2007.

"This information is important because it indicates the significant degree to which people and pets are being exposed to tick-borne diseases, and therefore, the risk of developing some very serious illnesses," Little adds. "As veterinarians, we need to incorporate this information into our practice, continuing to stress the need for year-round tick control in dogs and the importance of routinely screening for ticks and tick-borne diseases."

Table 1: Percentage of Positive Test Results for Lyme disease, anaplasmosis and ehrlichiosis

Dr. Mike Paul, executive director of the Companion Animal Parasite Council, agrees.

"These diseases are ubiquitous. We have always believed they are somewhat uncommon in areas and very regionalized. This data is showing us that vector-borne disease is not as uncommon and not as localized as we thought," Paul tells DVM Newsmagazine.

Common tick species in North America causing the biggest problem include the American dog tick (Dermacentor variabilis), the black-legged tick or deer tick (Ixodes scapularis in the East, Pacificus in the West), and the brown dog tick (Rhipicephalus sanguineus).

To better understand where these problem ticks are migrating, the testing results of domestic dogs from thousands of veterinary practices across the United States were compiled for this national prevalence study. Test results were generated from the company's reference laboratory network and through reported results from its SNAP 3Dx and SNAP 4Dx tests.

Some of the survey findings include:

Positive tests for Lyme disease were highest in the Northeast, while positive results for anaplasmosis were highest in the Midwest. In the Southeast, ehrlichiosis was most widely reported.

Numbers of Lyme-positive dogs in Connecticut (where 18 percent of the dogs were reported to test positive for Lyme) were from 50- to more than 200-fold greater than those in the southeastern border states of Texas, Louisiana, Mississippi, Alabama and Florida. Little was surprised also by the high prevalence of infection detected in the western states of Southern California, Arizona and New Mexico.

Milder northern climates, urbanization and mobile human/pet populations are fueling the geographic movement of parasites and transmission of tick-borne diseases, experts say.

In the South, the rate of ehrlichia- positive dogs was more than twice the national average. Cases of ehrlichiosis due to the E. canis pathogen are considered more common in the southern U.S. where infestations of the brown dog tick are more commonly seen, although in the absence of effective control programs, the brown dog tick can survive indoors in kennels and homes — virtually anywhere there are dogs. The report showed cases of heartworm in more than 3 million dogs in 48 states. Evidence of at least one agent was found in dogs from every state considered.