Following are highlights from the Companion Animal Parasite Council’s Lyme disease guidelines. Go to www.capcvet.org/capc-recommendations/lyme-disease for the complete guidelines.
Dogs and cats become infected with B. burgdorferi when feeding ticks inoculate the organisms. In North America, only Ixodes scapularis and Ixodes pacificus, the eastern and western black-legged tick, respectively, have been shown to transmit the infection to dogs.
- Most dogs exposed to B. burgdorferi appear to develop subclinical infections.
- Dogs with acute Lyme borreliosis may present with fever, shifting leg lameness, swollen joints, enlarged lymph nodes, lethargy, depression, and anorexia. In general, clinical improvement is observed following initiation of antibiotic therapy.
- Chronic disease is also associated with shifting leg lameness caused by transient, persistent polyarthritis accompanied by progressive joint changes; polyarthritis may persist even in the face of aggressive antibiotic therapy. Protein-losing glomerulopathy leading to acute progressive renal failure has also been described.
- Mild focal meningitis and encephalitis without concomitant neurologic signs have been described in experimentally, but not naturally, infected dogs.
Infection with B. burgdorferi is common in the Northeastern, Upper Midwestern, and West Coast states. In endemic areas, regional seroprevalence in dogs ranges from 1.4 percent in the West to as high as 13.3 percent in the Northeast. However, in nonendemic areas, such as the southern United States, infection is rarely documented in pets without a travel history to an endemic area.
Borrelia burgdorferi infection is more common in areas where tick infestation pressure is high and routine acaricide use is not practiced. In some surveys, over half of questing nymphal and adult ticks have been shown to harbor B. burgdorferi infections, creating a high risk of infection for pets living in a tick-infested environment.
A clinical diagnosis of Lyme borreliosis usually depends on the presence of compatible clinical signs and positive serology for B. burgdorferi. Although dogs with protein-losing nephropathy may develop azotemia, hypoalbuminemia, and proteinuria, hematology and serum chemistry do not reveal specific evidence of infection in most dogs with Lyme disease. Thromobocytopenia or leukopenia in a dog from an area where B. burgdorferi is endemic is more likely attributable to infection or coinfection with a rickettsial pathogen rather than an indication of Lyme borreliosis.
Serology is the mainstay of confirming a clinical impression of Lyme disease. Because of the prolonged incubation period, diseased dogs are almost always seropositive. However, because asymptomatic dogs in endemic areas are also often or even usually seropositive, accurate interpretation of a positive serologic test result is complicated.
- Sensitive and specific patient-side assays are available that identify the presence of antibodies caused by natural infection and not prior vaccination.
- It is important to remember that whole cell vaccines can invoke antibodies that are detectable by whole-cell-based indirect fluorescent antibody (IFA) or enzyme-linked immunosorbent assay (ELISA) tests. Therefore, previous vaccination or prior exposure to related organisms may result in false-positive test results when using whole-cell-based IFA or ELISA, necessitating a follow-up Western blot assay for any dogs testing positive on the initial whole-cell-based screening technique. For this reason, many veterinarians consider the specific C6-based assay the initial screening method of choice for evaluating a dog for exposure to and potentially infection with B. burgdorferi.
- The standard treatment for disease caused by B. burgdorferi infection in dogs is doxycycline at 10 mg/kg orally every 24 hours for 30 days. Longer courses of treatment may be necessary in some dogs, particularly those with nephropathy.
- Prophylactic use of antibiotics following a tick bite is not recommended in dogs given the high frequency of exposure in the face of a relatively low incidence of clinical disease. However, continued monitoring of such dogs for future signs of infection or disease may be warranted.
- Antibiotic treatment of a clinically normal, seropositive dog is controversial. Most seropositive dogs do not have any evidence of clinical disease. However, because the course of infection can be prolonged, treating in the subclinical phase is viewed by some veterinarians as potentially beneficial in preventing the development of chronic disease. Currently, CAPC recommends that seropositive dogs be tested for the presence of other, coinfecting tick-borne disease agents and for evidence of abnormalities on hematology or urinalysis and that a tick-control program be instituted. Antibiotic treatment of seropositive dogs in the absence of clinical or pathological abnormalities is not recommended. However, every conceivable precaution should be taken to minimize any chance that ticks could acquire B. burgdorferi from seropositive pets.
Control and prevention
- Vaccines are available to limit Lyme borreliosis in dogs, and experimental studies testing efficacies of some of these vaccines were reported in peer-reviewed journals. The decision to vaccinate against Lyme borreliosis should be based on a risk assessment of the individual dog that includes information about where the dog lives and how often it frequents a tick-infested area. Routine vaccination of dogs against Lyme disease is not warranted in areas of the United States where B. burgdorferi infection is not endemic.
- Vaccination against Lyme borreliosis does not replace the need for stringent tick-control programs in pets. Vaccines may not protect against all strains of B. burgdorferi, and ticks harbor multiple pathogens for which vaccines are not yet available. For this reason, CAPC recommends that all pets be maintained year-round on highly effective acaricides with residual activity against ticks.
- Attached ticks found on pets should be promptly removed to prevent transmission of B. burgdorferi or any other pathogens they may harbor. To avoid both zoonotic infection and accidental inoculation of pathogens into the pet during the removal process, ticks should be retracted using forceps or a commercial tick-removal device, and care should be taken to avoid contact with tick contents, ideally by wearing gloves. Careful attention to handwashing following tick removal is also recommended.
- Tick infestations and resultant infection with B. burgdorferi can be prevented by avoiding tick-infested areas whenever possible and by modifying the habitat around the home through such basic measures as keeping shrubbery and grass closely clipped to discourage both tick populations and the wildlife species that often harbor them from flourishing. Immature ticks on rodents may be controlled through the use of acaricide-treated cotton that the rodents then use to line their nest, or by bait stations constructed to allow self-application of acaricides to rodents. Broadcasting acaricides across large outdoor areas is difficult, expensive, and largely ineffective in controlling many tick species.
The Companion Animal Parasite Council is an independent, non-profit council established to create guidelines for the optimal control of internal and external parasites that threaten the health of pets and people, and to bring together broad expertise in parasitology, internal medicine, public health, veterinary law, private practice and association leadership. Learn more at www.capcvet.org/about-capc.