With more than 20,000 human cases reported annually, Lyme disease is the most common vector-borne disease in the U.S., according to the U.S. Centers for Disease Control and Prevention.
On the canine end, however, the number of Lyme-infected dogs is unclear because of the lack of a central reporting agency.
Experts have found that veterinarians practicing in areas thought to be relatively free of Borrelia burgdorferi aren’t looking for Lyme disease. And in Lyme-endemic areas, the experts say, the disease may be overdiagnosed and overtreated in dogs.
Though 95 percent of Lyme cases are found in just 12 states, specialists say using a single test—the SNAP-4Dx by Idexx Laboratories of Westbrook, Maine—can detect multiple vector-borne diseases. That means the bacteria/parasite presence in a particular region can be easily determined.
“Veterinarians can take pre-emptive measures to detect exposure in pets, help draw conclusions if illness is present, and as public health professionals, use canine patients as sentinels for disease in the region,” says Andrew Eschner, DVM, senior technical services veterinarian at Merial USA of Duluth, Ga.
“This organism has evolved to live in specific hosts and it doesn’t want to kill the host animal. It has been present in humans for a shorter time, which is why people exposed to the bacteria almost always develop disease symptoms.”
According to the University of Pennsylvania, more than 60 percent of animal infectious diseases can infect humans. Since Lyme is a zoonotic disease, the research interest is strong.
In the Lab
Experimentally, adult beagles given Lyme disease did not get sick. They just became Lyme-positive, says Meryl P. Littman, VMD, Dipl. ACVIM, of Penn’s School of Veterinary Medicine.
“Beagle puppies that did get sick showed a four-day self-limiting lameness and fever, signs that went away without any treatment,” Dr. Littman adds. “There was no acute stage of illness—incubation was two to five months after the tick bite—no rash, no flulike signs, no cardiac or neurologic signs in the dogs. In the field we see the same: many asymptomatic Lyme-positive dogs.
“About 5 percent of exposed dogs get fever, anorexia, lameness, which responds fast to antibiotics (usually Doxycycline).
“Less common is Lyme nephropathy, often in Labradors and golden retrievers, which is a serious protein-losing kidney disease that may not respond to antibiotics because it is an immune-mediated disease triggered by exposure to Lyme antigens.
“Signs of other tick-borne diseases can include similar symptoms to Lyme disease. The diagnosis of Lyme is often made too fast, based on a Lyme positive test. The signs may actually be due to a co-infection with one of the many other tick-borne diseases in our area or some other disease process entirely.”
Research shows that dogs testing positive for both Lyme and Anaplasmosis are twice as likely to show clinical symptoms, says Leif Lorentzen, DVM, senior medical affairs manager at Idexx.
| The Eww! Factor
Some pet owners are turned off by the thought of applying a parasite-prevention chemical to their pet’s skin, says Roger Valentine, DVM, MS, NMD, of Whole World Wellness, a holistic practice in Santa Monica, Calif.
In these cases, some holistic veterinarians and clients who want to protect a pet are using a new product called shoo!TAG.
The manufacturer, Energetic Solutions LLC of Austin, Texas, says the device hangs from the collar and uses electromagnetic frequencies to repel ticks, mosquitoes and fleas.
“Some people don’t want the smell or an oily mess on their pet, or maybe they want to use something non-toxic on a cat,” Dr. Valentine says.
Adult and nymph tick lifestages can transfer Lyme disease, a fact many owners are unaware of, Valentine says.
“Nymphs are the size of a period and can easily go undetected,” he adds. “This product takes three days to activate, but then lasts for four months and stops the ticks from ever going onto a pet. This is an effective alternative for owners.”
“The organism that causes Lyme disease has been around for centuries but has been ecologically kept in check,” Merial’s Dr. Eschner says. “In the last 30 years or so the number of ticks that cause Lyme disease has increased. [They] are creeping in to new areas.”
Lyme in Dogs
Exposure to Lyme disease is common in dogs, but the disease isn’t, Littman says.
“Ninety-five percent of exposed dogs don’t get sick, but they become Lyme antibody-positive on tests, which may scare people into thinking they need to be treated,” she says. “We don’t treat asymptomatic dogs, but we check their urine for protein. In some areas in New England, 70 to 90 percent of healthy dogs are Lyme-positive. At PennVet, we found about 40 percent of healthy dogs are Lyme-positive in our area.”
Some specialists say tests such as the SNAP-4Dx should be used routinely to detect exposure to Lyme, heartworm disease, Ehrlichiosis and Anaplasmosis.
“Some other tests will show a false positive if an animal has been vaccinated for Lyme disease,” Dr. Lorentzen says. “The SNAP-3Dx and SNAP-4Dx tests use a synthetic peptide (C6) based on one of six invariable regions (IR6) within the variable domain of VlsE.
“VlsE, a unique surface lipoprotein of Borrelia burgdorferi, undergoes antigenic variation in the vector tick and is found in field-infected dogs, but not in vaccinated dogs or in dogs infected with in vitro-derived Borrelia.”
The website DogsAndTicks .com maps canine Lyme-positive test results in the U.S. using the SNAP-4Dx test. This is the closest thing to a central reporting agency dealing with the issue.
Lyme Vaccine or Not?
Some veterinarians believe that the Lyme vaccine for dogs is controversial and unnecessary when tick prevention is practiced. The vaccine is listed as a non-core vaccine on the American Animal Hospital Association’s canine vaccine guidelines and recommended only with a tick repellent.
“Lyme vaccination is still controversial because the most serious forms of Lyme disease in dogs are caused by an immune-mediated pathogenesis and don’t respond to antibiotics,” Penn’s Littman says. “I prefer not to use Lyme vaccines when topical repellents and collars can prevent a tick from attaching and kill it before transmission of organisms can occur. There are many other kinds of tick-borne diseases in our area, so we need to use good tick control anyway.”
Recombitek Lyme is the only vaccine that contains outer surface protein A (OspA) in a nonadjuvanted formula, according to Merial, the manufacturer.
OspA is the only antigen needed to stimulate protection against Lyme disease in North America, Merial’s Eschner says.
“Immunization coupled with tick control is the best prevention, especially in areas of high risk,” he says. “Clients in Lyme-endemic areas know of the disease and want to protect their pets, but veterinarians need to discuss all possible options and their pros and cons.
“The acronym VET (vaccinate, educate, tick control) reminds veterinarians that a multimodal approach gives patients and clients the best assurance of protection.”
Ira G. Roth, DVM, director of the University of Georgia’s Community Practice Clinic, says the Lyme vaccine doesn’t get much use there.
“Veterinarians should be prudent with suggestions to clients and look at individual patient needs over sticking to a strict protocol,” Dr. Roth says. “There are only about a dozen positive cases at the university a year. We recommend prevention and simply putting your hands on the pet every day to check for problems.”
The Ixodes tick, also known as the deer or black-legged tick, uses different animals for different life stages and when its preferred host isn’t readily available. The term “deer tick” is a regional reference that can delude pet owners into thinking their pets aren’t at risk if they don’t live near deer or wooded areas. The problem is, birds also are carriers.
“Bird migration can bring the Ixodes ticks to your neighborhood,” Littman says. “Robins have been found to harbor these ticks, so even if there are no deer, there are always birds around to bring these ticks to your back yard.”
What About Cats?
According to the experts, cats are minor Lyme disease players. Many of the tick repellent agents are toxic to cats, so their owners must use caution.
“We recommend tick prevention be used year-round on dogs and cats,” says Michael J. Yabsley, MS, Ph.D., an assistant professor of wildlife disease ecology at Georgia’s veterinary college. “Fipronil and selamectin are relatively safe insecticides for feline and canine use that, when used properly, will prevent the transmission of the causative agent of Lyme disease.
“Tick prevention for cats in the South has a heightened importance because of Cytauxzoon felis. This tick-borne parasite results in a very high mortality among infected cats but is very preventable. It’s a very sad disease and is an important reason to keep ticks off cats.”
“Seropositive dogs are sentinels that the owner lives in a Lyme-endemic area, but owners should know they won’t get Lyme disease from their dog,” Littman says. “If a tick repellent is used on the dog, the ticks won’t be able to attach to the dog and their mouthparts will be paralyzed after exposure to the product, so they won’t attach to people, either.”
Elizabeth Hodgkins, DVM, Esq., veterinary services manager at Summit VetPharm of Rutherford, N.J., says all staff members should be educated in tick-borne diseases and know the prevalence of Lyme disease in their area.
“Compliance is a direct function of awareness of the repercussions of not taking precautions and using preventions,” Dr. Hodgkins says. “About half of noncompliant owners are [noncompliant] due to a lack of understanding.”
The U.S. Environmental Protection Agency has intensified its evaluation of spot-on pesticide products for flea and tick control because of an increase in reported incidents, agency spokesman Dale Kemery says. A technical evaluation and review by veterinarians, the EPA, Health Canada and manufacturers looked into adverse reactions ranging from skin irritation to seizure to a pet’s death. “The majority of the incidents reported to EPA are related to flea and tick treatments with EPA-registered spot-on products,” Kemery says. “The report results are expected to be announced soon.”
Veterinary experts say all pharmaceuticals can be dangerous, especially if used improperly.
“The risk of disease is far greater than experiencing a harmful side effect,” Hodgkins says. “I hope the report isn’t presented in a way to scare consumers from using spot-on flea and tick preventives. Veterinarians need to discuss risk versus benefit for all drugs.”
To avoid improper application of tick products, owners should be instructed in their use, not simply expected to read the literature, she adds.