April 5, 2012
An unseasonably warm U.S. winter not only has meant non-stop tick-sightings, it could mean a boom in the parasite population this spring—or sooner, parasitologists say. This correlates with a higher prevalence of tick-borne diseases in dogs and humans.
While dogs present with different symptoms based on the type of tick-borne disease they’ve contracted, one common presentation is fever. Experts say the variety of symptoms makes a diagnosis difficult, especially because co-infections are the norm in dogs.
“When dogs are exposed to more than one tick-borne pathogen, they’re at an increased risk of clinical disease,” says Melissa Beall, DVM, Ph.D., medical affairs manager at Idexx in Westbrook, Maine. “We conducted research in Minnesota that showed dogs with co-infections had more severe disease presentations. Having more than one condition impacts the animals’ ability to manage disease.”
Edward Breitschwerdt, DVM, a professor at North Carolina State University and adjunct professor of medicine at Duke University Medical Center, played a major role in orchestrating the seventh International Conference on Bartonella as Animal and Human Pathogens (April 25-28). He warns that ticks carry at least 15 known pathogens that can be transmitted to a dog.
“We’re finding more and more that ticks and fleas are doing things we never before knew about,” Dr. Breitschwerdt says. “Ticks are expanding their domains, possibly by hitching rides on migrating animals or animals in wildlife relocation programs. These factors, coupled with people moving outward into tick-endemic areas, have resulted in higher risk of tick-borne disease transfer to animals and humans.
“It’s not just deer, it’s opossums, raccoons, birds, coyotes and other animals that can transfer ticks from one place to another,” Breitschwerdt continues. “With new housing developments forming in areas previously uninhabited by people, ticks are being dropped in yards by wildlife.”
The Lone Star tick has made a progressive northward migration, while Lyme disease has been diagnosed in every state, Breitschwerdt says. The black-legged (or deer) tick also has an increasing range.
Thomas Mather, Ph.D., of the University of Rhode Island in Kingston, was awarded an $875,000 grant from the Centers for Disease Control to conduct studies and develop tools that will help Rhode Island residents choose the best tick-control strategies for their needs.
“I give speeches on more ticks in more places regularly to increase awareness of prevention of tick bites and pathogen transmission,” Mather says. “It’s still accurate to say that certain species remain true to certain areas, but each year there is a clear increasing trend in tick encounters.
“When comparing U.S. encounters with ticks in comparison to that of Europeans, many more U.S. residents encounter ticks in their own backyard whereas Europeans have tick run-ins when hiking or camping,” Mather adds.
Mather and other experts say because ticks are commonly encountered in the U.S., veterinarians are in a prime position to educate and report on the types of species being found and the diseases being diagnosed.
“Vets should educate owners as they travel more with their pets,” says Patricia Conrad, DVM, Ph.D., professor of parasitology in the School of Veterinary Medicine at the University of California, Davis. “With many U.S. pet owners taking pets along and hotels catering to this need, vets and owners should communicate so owners know of potential tick risks.”
Experts say that the extensive tick information now available can overwhelm the average pet owner.
“More often than not, an owner doesn’t take the opportunity to use prevention—or start when she sees her pet has been exposed to ticks,” Dr. Conrad says. “A tick can drop off so sometimes when a sick animal comes to the vet practice, there are no ticks, but owners don’t realize it only takes one bite from a contaminated tick to cause disease.”
Ticks You Love to Hate
˜Dermacentor variabilis (American dog tick) is a vector for Rocky Mountain spotted fever and tuleremia and may carry human granulocytic ehrlichiosis.
˜Ixodes scapularis (black-legged tick) is a vector for Lyme disease, babesiosis, ehrlichiosis.
˜Dermacentor andersoni (Rocky Mountain wood tick) is a vector for Rocky Mountain spotted fever, tularemia, Colorado tick fever and a major cause of tick paralysis.
Experts say veterinarians also need to help their community be safe. Mather suggests veterinarians offer to write a weekly newspaper column that can include information on tick-borne disease prevention.
“Currently the only tick-borne disease that can be prevented for dogs with a vaccine is Lyme disease,” Breitschwerdt says. “There’s been difficulty finding efficacious vaccines for other tick disease prevention. With viruses, veterinarians expect 100 percent accuracy. We haven’t found that yet for tick-borne disease vaccines.”
Michael Stone, DVM, Dipl. ACVIM, clinical assistant professor with research interest in tick-borne diseases in dogs at Cummings School of Veterinary Medicine at Tufts University, says veterinary-recommended flea and tick preventive products are highly effective.
“Of course, no product is 100 percent effective, but regular use greatly decreases the number of parasites that can live on the pet,” Dr. Stone says. “This, in turn, decreases the chances that the pet owner may be bitten.”
Experts say the best way for veterinarians to encourage pet owners’ compliance is conveying to them the basics of tick life.
“Understanding the biology and ecology of a tick will go a long way in helping pet owners understand how resilient they are and that a tick isn’t always big enough to see easily, and with each stage; the tick chooses a new host to feed on,” Conrad says.
“Lyme disease (borreliosis) and anaplasmosis are the most common tick-borne disease diagnosed in dogs,” Stone says. “Lyme disease does not cause clinical illness in cats. In dogs, the most common signs of infection are lameness, decreased appetite and listlessness.
“Anaplasmosis presents similarly to Lyme, with listlessness, decreased appetite and lameness being common signs,” Stone continues. “We are beginning to recognize anaplasmosis in cats, although not at the frequency we diagnosis the infection in dogs. Anaplasmosis can cause serious illness in humans.”
The standard treatment for disease caused by B. burgdorferiinfection in dogs is doxycycline at 10 mg/kg orally every 24 hours for 30 days.
“Nephropathy is about the worst thing that can happen to a dog infected with Lyme disease,” Breitschwerdt says.
Several species of ticks are known to transmit the zoonotic parasitic disease Rocky Mountain spotted fever.
“Ticks may acquire the Rickettsia rickettsii organism by feeding on parasitemic small mammals such as rats, chipmunks and squirrels,” Breitschwerdt says.
This disease is typically found in the eastern U.S.
In the South, the rate of Ehrlichia-positive dogs is more than twice the national average. But all Ehrlichia spp. and Anaplasma spp. infections in dogs and cats respond to doxycycline.
A treatment regimen of 10 mg/kg for 28 days is recommended by the Companion Animal Parasite Council.
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