Abstract
BackgroundDogs in the US are commonly infected with vector-borne pathogens, including heartworm and tick-borne disease agents. The geographic distribution of both arthropod vectors and the pathogens they transmit continues to expand.MethodsTo describe the current geographic distribution and prevalence of antigen of Dirofilaria immitis and antibody to Borrelia burgdorferi, Ehrlichia spp., and Anaplasma spp. in dogs, we summarized over 144 million test results from 2013 to 2019, inclusive, by county, state, and region. Canine seroprevalence by state was compared to population-adjusted human reports of tick-borne diseases.ResultsResults varied regionally, with D. immitis antigen and Ehrlichia spp. antibodies more frequently detected in the Southeast (2.6% and 5.2%, respectively) and antibody to B. burgdorferi and Anaplasma spp. most common in the Northeast (12.1% and 7.3%, respectively). Overall, percent positive test results to D. immitis decreased in the Southeast by 33.3% when compared to earlier summaries using the same strategy (from 3.9 to 2.6%). Geographic expansion of areas where dogs commonly test positive for Ehrlichia spp. was evident, likely because of a change in the test made in 2012 to allow detection of antibodies to E. ewingii concomitant with expansion of vector tick populations. Percent positive test results to Ehrlichia spp. increased in every region; this shift was particularly pronounced in the Southeast, where percent positive test results increased fourfold (from 1.3 to 5.2%). Continued geographic expansion of B. burgdorferi and A. phagocytophilum was apparent in the Northeast, Midwest, and Upper South, although canine seroprevalence of antibody to B. burgdorferi was much lower than prior surveys in many Lyme-endemic areas. Annual reports of human cases of Lyme disease, ehrlichiosis, and anaplasmosis were associated with percent positive canine results by state for the three tick-borne disease agents (R2 = 0.812, 0.521, and 0.546, respectively). Within endemic areas, percent positive test results for all three tick-borne agents demonstrated evidence of geographic expansion.ConclusionsLarge scale analysis of results from screening dogs in practice for evidence of vector-borne infections, including those with zoonotic importance, continues to be a valuable strategy for understanding geographic trends in infection risk over time.Graphical
Highlights
Dogs in the US are commonly infected with vector-borne pathogens, including heartworm and tick-borne disease agents
Each year in the US, millions of dogs are tested for antigen of heartworm (Dirofilaria immitis) and antibody to tick-borne disease agents, most commonly Borrelia burgdorferi, agent of Lyme borreliosis; Anaplasma spp., which cause anaplasmosis in people and animals; and Ehrlichia spp., causative agents of human and canine ehrlichiosis [1, 2, 4, 5]
Source of data Results for the present analysis and summary (2013– 2019) were generated using USDA-licensed test kits (IDEXX Laboratories, Inc.) and included: SNAP® 4Dx® Plus Test kit, an in-clinic enzyme-linked immunosorbent assay (ELISA) for detection of D. immitis antigen and canine antibodies to B. burgdorferi, Ehrlichia spp. (E. canis, E. ewingii), and Anaplasma spp. (A. phagocytophilum and A. platys); SNAP® HW RT Test kit, an in-clinic ELISA for the detection of D. immitis antigen in canine serum, plasma, or whole blood
Summary
Dogs in the US are commonly infected with vector-borne pathogens, including heartworm and tick-borne disease agents. Despite the widespread availability of preventives, ticks are common on dogs across the USA, and evidence suggests the prevalence of heartworm infection and of antibodies to tick-borne disease agents is increasing in some regions [9,10,11,12]. These increases likely result from a combination of factors including increased vector populations, resulting in more intense transmission, geographic spread of natural maintenance cycles for infection, and translocation of infected dogs [11,12,13,14,15,16]. We update our earlier publications by reporting the percent positive test results of dogs evaluated by veterinarians in the US from 2013 to 2019, documenting continued changes in both distribution of these infections and overall infection risk
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