Tracking Lyme Disease in Dogs May Help Protect Humans

By Steven Reinberg
HealthDay Reporter

WEDNESDAY, Aug. 10 (HealthDay News) — Tracking Lyme disease infections in dogs may help scientists predict possible outbreaks of the tick-borne illness in humans, government researchers report.

Since dogs are also susceptible to Lyme disease, they can be a good indicator of the risk of human infection, the scientists from the U.S. Centers for Disease Control and Prevention said. When blood tests show that few dogs in a given area carry the bacteria, the risk to people is relatively low, they noted. Conversely, when more dogs test positive for Lyme, people may be at increased risk, they noted.

“Public health authorities could use this to assess and evaluate changes in their region,” said Dr. Gary P. Wormser, chief of infectious diseases at New York Medical College and Westchester Medical Center in Valhalla. “This could be of help in understanding the risk areas for humans.”

The report, released Aug. 10, is published in the September issue of the CDC journal Emerging Infectious Diseases.

For the study, a team led by Dr. Paul Mead, a CDC medical epidemiologist, used data from 46 states on human and canine Lyme disease prevalence.

Comparing the data, Mead’s team found that when 1 percent or less of the dogs tested positive for Lyme disease, the risk of people becoming infected was low. However, when more than 5 percent of the dogs were infected, the risk to people was high.

A 5 percent (or higher) rate of positive blood test results in dogs “can be a sensitive but nonspecific marker of increased risk for human Lyme disease,” the researchers wrote in a CDC news release. “Because dogs do not transmit infection directly to humans [or humans to dogs], this association reflects similar susceptibilities to tick-borne infection.”

Sometimes, this level of canine infection “appears to anticipate increasing rates of human infection at the county level. Conversely, canine [prevalence of 1 percent or less] is associated with little to no local risk for human infection,” Mead’s group concluded.

Blood tests can detect a dog’s exposure to the bacteria, even when no symptoms appear. “Most of the time the dogs appear to be asymptomatic, but they do develop clinical disease as well,” Wormser said. As a result, they may develop problems walking and possibly heart or kidney complications.

Like humans, dogs with the disease can be treated with antibiotics. “There is also a vaccine for dogs,” Wormser said. Symptoms may abate without treatment, but Lyme disease can leave recurrent lameness.

Commenting on the study, Phillip J. Baker, executive director of the American Lyme Disease Foundation, said, “You have to wonder if a dog is a good sentinel animal.”

Their travel history and the use of tick repellent can affect estimates of Lyme disease prevalence in a specific area, he explained.

To prevent being bitten by the deer tick, which spreads Lyme disease, Baker advises checking your pet (and yourself) after walking through woods, fields or tall grass. Many dog owners also use tick repellent on their pets, he said.

Areas where cattle and goats are raised may have a reduced risk of Lyme disease, according to another study in the same journal issue.

Researchers from Charite Universitatsmedizin Berlin in Germany found pastures containing livestock bore fewer ticks in general and fewer ticks carrying Lyme disease. Hikers passing through these pastures were 40 to 54 times less likely to contract Lyme disease than those walking through meadows or fallow land, they said.

It’s possible that grazing animals reduce the tick’s habitat or perhaps the ticks shed the Lyme disease bacteria when they feed on animals, the researchers said.

“Extensive landscape management that uses domestic ruminants not only serves to maintain cultural and natural heritage in Germany but also seems to confer a health benefit for hikers and others seeking recreation,” the researchers wrote in the CDC news release.

More information

For more on Lyme disease, visit the U.S. National Library of Medicine.

SOURCES: Gary P. Wormser, M.D., chief, infectious diseases, New York Medical College and Westchester Medical Center, Valhalla, N.Y.; Phillip J. Baker, Ph.D., executive director, American Lyme Disease Foundation, Lyme, Conn.; September 2011 Emerging Infectious Diseases

Last Updated: Aug. 10, 2011