Tick-Borne Diseases Reported in Most States, Expert Saysby Dr. Susan E. Little
ORLANDO, Fla. — A new study supports what experts have been saying — ticks are moving into new areas and bringing new diseases. A national survey of veterinary clinics found positive tests for Lyme disease, anaplasmosis and ehrlichiosis present in most states.
“We’re seeing a huge tick expansion, and we’ve seen tick species move into new areas,” said Susan E. Little, DVM, PhD, DEVPC, here at the NAVC Conference. “Amblyomma americanum, which is the Lone Star tick, historically a southern tick, has been reported as far north as Maine. A. maculatum, the Gulf Coast tick, has been established in Kansas and reported in Nebraska, Tennessee and Georgia.”
The study results, presented by Little in a symposium sponsored by IDEXX Laboratories, were part of a voluntary reporting system developed by IDEXX. The results of testing domestic dogs from thousands of US veterinary practices were compiled from 2001 to mid-2007. Test results were generated from IDEXX’s reference laboratory network, as well as in clinics testing with the SNAP 3Dx and 4Dx.
“This was a novel approach in veterinary medicine, and I’m sure many of you participated in the program. When you did the diagnosis using 3Dx and 4Dx assays, you submitted the results to IDEXX, which collated all the data and kept track, then turned those numbers over to the CAPC [Companion Animal Parasite Council],” Little said. “Data were collected for more than 3 million dogs. We have tick-borne disease data on about 1 million for Borrelia and Ehrlichia and about half a million on Anaplasma. We took those numbers and looked at geographic trends,” said Little, of the department of pathobiology at the Center for Veterinary Health Sciences at Oklahoma State University.
Overall, positive tests for Lyme disease were highest in the Northeast, positive results for anaplasmosis were highest in the Midwest and positive results for ehrlichiosis in the Southeast.
The number of dogs that tested positive for Lyme disease in Connecticut, where 18% of the dogs tested pos¬itive for the disease, were up to 200-fold greater than those in the South.
The percentage of positive tests for Lyme disease were 11.6% in the Northeast, 4% in the Midwest, 1.4% in the West and 1% in the Southeast.
The maps show the percentage of positive test results from domestic dogs in thousands of veterinary practices across the country. Positive results are shown for Lyme disease, anaplasmosis and ehrlichiosis by region with the Northeast seeing the most Lyme disease, the Midwest seeing the most anaplasmosis and the South seeing the most ehrlichiosis. Source: Idexx Laboratories.
Veterinarians should consider Lyme disease as a possible diagnosis in a dog with clinical signs, especially if the animal is from an endemic area, she said. “Dogs present with fever, shifting leg lameness and polyarthritis and are in overall poor health,” Little said. “Often, they become anorectic and might have some swollen lymph nodes. With chronic infections, we don’t see [the manifestations of] heart and neurologic disease in dogs that are reported in people, but we do see renal involvement.”
Ehrlichiosis and Anaplasmosis
In the South, the rate of Ehrlichiapositive dogs was more than twice the national average. Cases of ehrlichiosis caused by E. canis are considered more common in the South, where infestations of the brown dog tick occur more often. The study found that the percentage of positive tests for ehrlichiosis was 1.3% in the South, 0.6% in the West, 0.4% in the Midwest and 0.3% in the Northeast.
Little called anaplasmosis “the new kid on the tick-borne disease block.” The disease presents similar to ehrlichiosis, with fever, anorexia and classic thrombocytopenia. There may be swollen joints, depression and enlarged lymph nodes, too. Because Anaplasma is transmitted by Ixodes, the same tick that transmits Borrelia burgdorferi, it is not surprising that the highest concentration of anaplasmosis was found in the Midwest, Northeast and California.
The study found the percentage of positive tests for anaplasmosis was 6.7% in the Midwest, 5.5% in the Northeast, 4.5% in the West and 0.5% in the South. In addition, 2% of dogs in the Midwest and 1.4% of dogs in the Northeast tested positive for Anaplasma and Borrelia.
Doxycycline at 10 mg/kg is still the treatment of choice for these diseases, and treatment should last 28 days. “Shorter courses are not believed to be effective at clearing infection, and a lot of data support that. New data show that longer courses may be necessary to clear some infections because persistence might occur with all these diseases following treatment.”
The CAPC recommends year-round tick preventatives everywhere, and Little said the new data support that recommendation. “These little disease-carrying tanks are the source of infections,” she said.
Veterinarians should keep tick-borne diseases in their differential diagnosis even if they do not practice in an endemic area. “Although the diseases are regional, the dogs aren’t. They tend to move around, and we need to take that into account. In addition, diseases move into areas where they weren’t previously recognized,” she explained. “Veterinarians are the ones who will recognize them when they arrive because physicians aren’t testing as thoroughly — nothing like the routine testing many of us recommend for tick-borne diseases.”
Dr. Little has received funding to support research, consulting and presentations on behalf of a number of veterinary diagnostic and pharmaceutical companies, including IDEXX Laboratories. The CAPC also is supported by the veterinary health industry.
For more information:
Little S. Tick-borne disease: incidence and implications for understanding Lyme disease, ehrlichiosis, and anaplasmosis in dogs in the northern U.S.
Little S. Tick-borne disease: incidence and implications for understanding Lyme disease, ehrlichiosis, and anaplasmosis in dogs in the southern U.S.
Both presented at: The NAVC Conference. Orlando, Fla.; Jan. 19-23, 2008.
This was an interview with Susan E. Little, DVM, PhD -Department of Veterinary Pathobiology, Center for Veterinary Health Sciences, Oklahoma State University, Stillwater, Oklahoma
by Marie Rosenthal, MS, Executive Editor, Veterinary Forum. Appeared in April, 2008. Used by permission.