Borrelia (Lyme Disease)
Vaccination for Lyme borreliosis should be considered for dogs that live within or travel to regions with emerging or endemic Lyme disease. Lyme disease is caused by infection with tick-transmitted borrelial pathogens. Although at least 21 species of borrelial pathogens can cause Lyme disease, in North America disease is due almost exclusively to Borrelia burgdorferi.55,56 In 2014, species in the B burgdorferi sensu lato complex were awarded a new genus designation, Borreliella. However, this nomenclature is not yet routinely used by veterinarians and B burgdorferi refers to either.56
Lyme disease is transmitted by the bite of Ixodid ticks.55 In the northeastern, mid-Atlantic, and north-central United States and eastern Canadian provinces, the primary vector is Ixodes scapularis (black-legged tick, or deer tick), whereas on the Pacific coast, the primary vector is Ixodes pacificus (western black-legged tick). Although the geographic expansion of endemic areas may well occur, currently infections are largely restricted to clusters of states where these ticks, and appropriate mammalian disease hosts, are abundant.
Dogs that spend time outdoors in endemic regions are most likely to benefit from vaccination. Vaccination should be complemented with an ectoparasite control program as prevention of tick feeding prevents disease transmission.57,58 For dogs with travel planned to an endemic area, both initial vaccinations should be completed 2 to 4 wk before travel. In a recent large dataset (2013–2019), states with ≥5% seroprevalence in tested dogs included (in order of highest to lowest prevalence) Connecticut (15.5% seroprevalence), Massachusetts, Vermont, Maine, Pennsylvania, New Hampshire, Rhode Island, New York, New Jersey, West Virginia, Minnesota, Virginia, Maryland, Delaware, Wisconsin, and District of Columbia.59 In Canada, the disease is endemic in portions of Manitoba, eastern Ontario, southern Quebec, Nova Scotia, and New Brunswick.60,61 Dogs can serve as sentinels for infection in humans for this zoonotic disease, and regions with the greatest canine seroprevalence mirror regions with more human infections.59,62 Fortunately, although Lyme disease is zoonotic, there is no direct transmission from infected dogs to people, and infection in either species depends on vector transmission.63
Most dogs infected with B burgdorferi remain healthy.63 Only ≤10% develop a polyarthritis that is responsive to antimicrobial therapy.63 The most important potential consequence of infection is protein-losing nephropathy. For the estimated 1 to 5% of infected dogs that develop Lyme nephritis, the outcome is often fatal despite antimicrobial therapy.63–65 Predisposition to Lyme nephritis has been suggested for retriever breeds, perhaps warranting additional consideration for vaccination in these breeds.63,64,66
There are four types of Borrelia vaccines approved for use, each of which has been proved safe and efficacious. Vaccines for prevention of Lyme disease exert their protective effect in an unusual way. All available vaccines can induce canine antibodies that bind borrelial outer surface proteins that are expressed while the pathogen is in the tick (OspA). Having only OspA in a vaccine has been shown to be effective.67 It is also known that lipidation is a determinant of immunogenicity, and the lipidated recombinant OspA-only vaccine elicits a robust immune response.68 Some vaccines can also induce antibodies to an antigen that is expressed shortly after transmission to the dog (OspC).56,69,70 When the tick ingests antibodies to OspA from the vaccinated dog while feeding, the bacteria are killed before transmission. Antibodies to OspC extend protection against any bacteria that were not successfully killed inside the tick, thus acting synergistically with antibodies to OspA.69,70
Antibodies induced through vaccination may or may not result in positive serologic tests depending on test methodology.63,71–73 It is important to understand the impact of vaccination on tests used for either screening or disease diagnosis. Differentiation of vaccination from infection is possible for B burgdorferi.