Seroprevalence and evaluation of risk factors associated with seropositivity forBorrelia burgdorferiin Ontario horses

Abstract

Background Recently, the blacklegged tick (Ixodes scapularis), which is the vector of Borrelia burgdorferi, has undergone a range expansion from the northeastern and mid‐west United States to areas of southeastern Canada, including parts of Ontario. Understanding the seroprevalence of antibodies against B. burgdorferi in horses and risk factors for exposure is important for monitoring and preventing this emerging disease. Study design Cross‐sectional study of 551 horses in southern, central, and eastern Ontario, Canada. Objectives To assess the seroprevalence of B. burgdorferi in horses in Ontario, Canada; to evaluate risk factors associated with seropositivity; and, to compare the performance of two diagnostic tests. Methods Serum samples were obtained from clinically healthy horses in Ontario, Canada, along with completed questionnaires that were used for the risk factor analysis. Sera were tested with a Multiplex ELISA (Animal Health Diagnostic Center, Cornell University) and C6 ELISA (IDEXX SNAP® 4Dx® Plus test, IDEXX Laboratories). Results The seroprevalence of B. burgdorferi on at least one test was 17% (91/551), though only 15 (16%) horses tested positive with both tests. A spatial cluster of cases was detected in Eastern Ontario. The odds of being seropositive for B. burgdorferi on the C6 ELISA were significantly increased when oak trees were present by pastures (OR = 7.3 (1.8‐29.2), P = .005), while the odds were significantly decreased when regular tick checks were performed (OR = 0.1 (0.01‐0.7), P = 0.02). Main limitations Recruitment focused on known areas with blacklegged ticks as well as areas of higher horse density, which may have led to selection bias. Conclusions The expansion of blacklegged tick populations poses an ongoing risk for horses. Assessment of diagnostic testing options and risk factors is important for diagnosis and prevention, and with further investigation this information may be used to propose changes in management.

Equine attachment site preferences and seasonality of common North American ticks: Amblyomma americanum, Dermacentor albipictus, and Ixodes scapularis

“…In areas where Lyme disease is endemic or emerging, horses in pastures with oak trees are significantly more likely to be seropositive for B . burgdorferi [ 5 ]. Tick control practices were not recorded for the horses surveyed in the present study and likely varied between premises, but ticks were still commonly found (Table 1 ).…”

“…Ticks commonly infest horses in North America, causing localized inflammation and dermal trauma, and sometimes resulting in transmission of pathogens or systemic reactions [ 1 – 5 ]. Ixodid ticks most frequently identified from horses in the USA include Ixodes scapularis , which transmits Borrelia burgdorferi and Anaplasma phagocytophilum , both of which have been shown to cause equine disease; Amblyomma americanum , which can induce localized reactions; and Dermacentor variabilis , a species associated with equine tick paralysis and experimentally competent for transmission of Theileria equi [ 1 , 3 , 6 – 10 ].…”

Evaluation of 2 ELISAs to determine Borrelia burgdorferi seropositivity in horses over a 12-month period

“…10,12,18 The agreement between these 2 serologic tests and their ability to detect B. burgdorferi infections can vary, and few studies have analyzed B. burgdorferi antibodies in horses at more than one time. 16 Our objectives were to evaluate B. burgdorferi seropositivity in naturally exposed horses over a 12-mo period, and to determine the repeatability of these 2 common serologic tests using paired serum samples.…”

“…7,8,14 Using 2 ELISAs, a 2020 study in Ontario found 17% seroprevalence of B. burgdorferi in clinically healthy horses, although there were discrepancies in agreement between the 2 serologic tests used. 16 Additionally, a gold standard testing method does not exist for horses, which complicates clinical testing and assessment of available tests. 8 Two main Lyme disease serologic tests are used in North America.…”

“…Horses that had been identified as positive on a multiplex ELISA or C6 ELISA during a 2016 prevalence study in Ontario, Canada, were eligible for enrollment. 16 Twenty-two of 91 (24%) seropositive horses were available for retesting 1 y after the initial test. Our study was approved by the University of Guelph Animal Care Committee (Animal Use Protocol 3257).…”