A Bayesian spatio-temporal model for forecasting Anaplasma species seroprevalence in domestic dogs within the contiguous United States

PLOS ONE, Dec 2019

This paper forecasts the 2016 canine Anaplasma spp. seroprevalence in the United States from eight climate, geographic and societal factors. The forecast’s construction and an assessment of its performance are described. The forecast is based on a spatial-temporal conditional autoregressive model fitted to over 11 million Anaplasma spp. seroprevalence test results for dogs conducted in the 48 contiguous United States during 2011–2015. The forecast uses county-level data on eight predictive factors, including annual temperature, precipitation, relative humidity, county elevation, forestation coverage, surface water coverage, population density and median household income. Non-static factors are extrapolated into the forthcoming year with various statistical methods. The fitted model and factor extrapolations are used to estimate next year’s regional prevalence. The correlation between the observed and model-estimated county-by-county Anaplasma spp. seroprevalence for the five-year period 2011–2015 is 0.902, demonstrating reasonable model accuracy. The weighted correlation (accounting for different sample sizes) between 2015 observed and forecasted county-by-county Anaplasma spp. seroprevalence is 0.987, exhibiting that the proposed approach can be used to accurately forecast Anaplasma spp. seroprevalence. The forecast presented herein can a priori alert veterinarians to areas expected to see Anaplasma spp. seroprevalence beyond the accepted endemic range. The proposed methods may prove useful for forecasting other diseases.

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A Bayesian spatio-temporal model for forecasting Anaplasma species seroprevalence in domestic dogs within the contiguous United States

July A Bayesian spatio-temporal model for forecasting Anaplasma species seroprevalence in domestic dogs within the contiguous United States Funding: IDEXX Laboratories 2 . CSM was partially supported by Grant R 2 from the National 2 Yan Liu 1 2 Stella C. Watson 1 2 Jenna R. Gettings 1 2 Robert B. Lund 1 2 Shila K. Nordone 0 2 Michael J. Yabsley 2 Christopher S. McMahan 1 2 0 Department of Molecular and Biomedical Sciences, Comparative Medicine Institute, North Carolina State University, College of Veterinary Medicine , Raleigh, NC , United States of America, 3 Southeastern Cooperative Wildlife Disease Study, Department of Population Health, College of Veterinary Medicine and the Warnell School of Forestry and Natural Resources, The University of Georgia , Athens, GA , United States of America 1 Department of Mathematical Sciences, Clemson University , Clemson, SC , United States of America 2 Editor: J. Stephen Dumler, Johns Hopkins University , UNITED STATES - This paper forecasts the 2016 canine Anaplasma spp. seroprevalence in the United States from eight climate, geographic and societal factors. The forecast's construction and an assessment of its performance are described. The forecast is based on a spatial-temporal conditional autoregressive model fitted to over 11 million Anaplasma spp. seroprevalence test results for dogs conducted in the 48 contiguous United States during 2011±2015. The forecast uses county-level data on eight predictive factors, including annual temperature, precipitation, relative humidity, county elevation, forestation coverage, surface water coverage, population density and median household income. Non-static factors are extrapolated into the forthcoming year with various statistical methods. The fitted model and factor extrapolations are used to estimate next year's regional prevalence. The correlation between the observed and model-estimated county-by-county Anaplasma spp. seroprevalence for the five-year period 2011±2015 is 0.902, demonstrating reasonable model accuracy. The weighted correlation (accounting for different sample sizes) between 2015 observed and forecasted county-by-county Anaplasma spp. seroprevalence is 0.987, exhibiting that the proposed approach can be used to accurately forecast Anaplasma spp. seroprevalence. The forecast presented herein can a priori alert veterinarians to areas expected to see Anaplasma spp. seroprevalence beyond the accepted endemic range. The proposed methods may prove useful for forecasting other diseases. Institutes of Health. JRG is supported by The Boehringer Ingelheim Vetmedica-CAPC Infectious Disease Postdoctoral Fellowship. Introduction Canine anaplasmosis is caused by gram-negative intracellular bacteria of the family Anaplasmataceae within the order Rickettsiales [ 1 ]. Anaplasma spp. bacteria are transmitted through the bite of infected ticks, with different tick species transmitting distinct types of Anaplasma bacteria in different regions of the country. A. phagocytophilum is transmitted by Ixodes scapularis and I. pacificus and maintained in a vector-reservoir-host system similar to that of Borrelia burgdorferi (the causative agent of Lyme disease), with the highest canine A. phagocytophilum seroprevalence reported in the Northeast, upper Midwest and along the west coast of California [ 2 ]. Although an important canine pathogen, A. phagocytophilum is also zoonotic and causes human disease in the same regions where Lyme disease occurs. In contrast, A. platys is presumed to be transmitted by Rhipicephalus sanguineus, and has relatively low prevalence across the contiguous United States with a slightly higher prevalence seen in the southern states [ 2 ]. Dogs in the southern U.S. (Florida, Georgia, North and South Carolina, Tennessee and Texas) show equivalent seroconversion to both A phagocytophilum and A. platys [ 2 ], suggesting exposure to multiple tick vectors. Veterinary wellness exams commonly include annual screening for exposure to Anaplasma spp., as well as Ehrlichia spp., Borrelia burdgorferi and Dirofilaria immitis (heartworm disease agent) using a rapid, in-house enzyme-linked immunosorbent assay (ELISA) platform (SNAP14Dx1 and SNAP14Dx1 Plus Test, IDEXX Laboratories, Inc., Westbrook, ME, USA) [ 3, 4 ]. These tests detect antibodies to both A. phagocytophilum and A. platys on a single spot and therefore no in-house speciation is possible. Of four million dogs tested for exposure to Anaplasma spp. in 2015, over 100,000 dogs were seropositive. Seroreactivity on these tests are interpreted by veterinary clinicians to indicate tick exposure and a history of transmission of Anaplasma spp. Many, if not most, dogs remain asymptomatic following exposure to Anaplasma spp.. For example, in areas such as the northeastern US where disease is endemic, as many as 60% of dogs may have antibodies specific for Anaplasma spp. and the majority of these dogs do not have overt evidence of clinical disease [ 5, 6 (...truncated)


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Yan Liu, Stella C. Watson, Jenna R. Gettings, Robert B. Lund, Shila K. Nordone, Michael J. Yabsley, Christopher S. McMahan. A Bayesian spatio-temporal model for forecasting Anaplasma species seroprevalence in domestic dogs within the contiguous United States, PLOS ONE, 2017, Volume 12, Issue 7, DOI: 10.1371/journal.pone.0182028