RESEARCH Open Access Canine infection with Dirofilaria immitis, Borrelia burgdorferi, Anaplasma spp., and Ehrlichia spp. in the United States, 2010–2012 Susan E Little 1* , Melissa J Beall 2 , Dwight D Bowman 3 , Ramaswamy Chandrashekar 2 and John Stamaris 2 Abstract Background: The geographic distribution of canine infection with vector-borne disease agents in the United States appears to be expanding. Methods: To provide an updated assessment of geographic trends in canine infection with Dirofilaria immitis, Borrelia burgdorferi, Ehrlichia spp., and Anaplasma spp., we evaluated results from an average of 3,588,477 dogs tested annually by veterinarians throughout the United States from 2010 – 2012. Results: As in an earlier summary report, the percent positive test results varied by agent and region, with antigen of D. immitis and antibody to Ehrlichia spp. most commonly identified in the Southeast (2.9% and 3.2%, respectively) and antibody to both B. burgdorferi and Anaplasma spp. most commonly identified in the Northeast (13.3% and 7.1%, respectively) and upper Midwest (4.4% and 3.9%, respectively). Percent positive test results for D. immitis antigen were lower in every region considered, including in the Southeast, than previously reported. Percent positive test results for antibodies to B. burgdorferi and Ehrlichia spp. were higher nationally than previously reported, and, for antibodies to Anaplasma spp., were higher in the Northeast but lower in the Midwest and West, than in the initial report. Annual reports of human cases of Lyme disease, ehrlichiosis, and anaplasmosis were associated with percent positive canine test results by state for each respective tick-borne disease agent (R 2 = 0.701, 0.457, and 0.314, respectively). Within endemic areas, percent positive test results for all three tick-borne agents demonstrated evidence of geographic expansion. Conclusions: Continued national monitoring of canine test results for vector-borne zoonotic agents is an important tool for accurately mapping the geographic distribution of these agents, and greatly aids our understanding of the veterinary and public health threats they pose. Keywords: Anaplasma, Borrelia burgdorferi, Canine, Dirofilaria immitis, Ehrlichia Background In 2009, we reported results of a national veterinary clinic based survey of dogs in the United States for antigen to heartworm and antibody to tick-borne disease agents [1]. Based on reported results from testing over 3 million dogs from 2001 to 2007, this study was the first to document and map percent positive test results on a national level to four vector-borne disease agents, namely, Dirofilaria immi- tis, Borrelia burgdorferi, Anaplasma spp., and Ehrlichia spp. [1]. Dirofilaria immitis, the causative agent of heartworm disease, is transmitted to dogs by a number of different mosquito species and is present throughout much of the United States [2]. Borrelia burgdorferi and Anaplasma phagocytophilum are transmitted by Ixodes spp. ticks, while Ehrlichia spp. are known to be vectored by Rhipice- phalus sanguineus sensu lato as well as ticks in the genera Amblyomma, Dermacentor , and Ixodes [3,4]. Veterinarians and pet owners are aware of these infec- tions, and canine preventive medicine protocols commonly include recommendations for administering routine heart- worm prevention and tick control to dogs as well as vaccination to prevent transmission of B. burgdorferi, the agent of Lyme disease, in areas where transmission occurs [5]. However, not all dogs receive adequate veterinary care, * Correspondence: susan.little@okstate.edu 1 Department of Veterinary Pathobiology, Center for Veterinary Health Sciences, Oklahoma State University, Room 250 McElroy Hall, Stillwater, OK 74078, USA Full list of author information is available at the end of the article © 2014 Little et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Little et al. Parasites & Vectors 2014, 7:257 http://www.parasitesandvectors.com/content/7/1/257