Abstract
Tick-borne diseases are a growing public health concern as their incidence and range have increased in recent decades. Lyme disease is an emerging infectious disease in Canada due to northward expansion of the geographic range of Ixodes scapularis, the principal tick vector for the Lyme disease agent Borrelia burgdorferi, into central and eastern Canada. In this study the geographical distributions of Ixodid ticks, including I. scapularis, and environmental factors associated with their occurrence were investigated in New Brunswick, Canada, where few I. scapularis populations have been found to date. Density of host-seeking ticks was evaluated by drag sampling of woodland habitats in a total of 159 sites. Ixodes scapularis ticks (n = 5) were found on four sites, Ixodes muris (n = 1) on one site and Haemaphysalis leporispalustris (n = 243) on 41 sites. One of four adult I. scapularis ticks collected was PCR-positive for B. burgdorferi. No environmental variables were significantly associated with the presence of I. scapularis although comparisons with surveillance data in neighbouring provinces (Québec and Nova Scotia) suggested that temperature conditions may be too cold for I. scapularis (< 2800 annual degree days above 0°C [DD > 0°C]) across much of New Brunswick. In contrast, the presence of H. leporispalustris, which is a competent vector of tularaemia, was significantly (P < 0.05) associated with specific ranges of mean DD > 0°C, mean annual precipitation, percentage of clay in site soil, elevation and season in a multivariable logistic regression model. With the exception of some localized areas, temperature conditions and deer density may be too low for the establishment of I. scapularis and Lyme disease risk areas in New Brunswick, while environmental conditions were suitable for H. leporispalustris at many sites. These findings indicate differing ecological niches for two tick species of public health significance.
Highlights
Ticks are vectors of bacterial, viral and protozoal pathogens of importance for human and animal health [1]
A total of 243 H. leporispalustris were found on 41 sites with a range of 1 to 67 ticks per site, which corresponds to 25.8% of all sites visited
Ixodes scapularis ticks were found in only 4 of 159 sites in this study, which suggests that populations of this tick are currently rare in New Brunswick and that risk from Lyme disease is mostly very low
Summary
Ticks are vectors of bacterial, viral and protozoal pathogens of importance for human and animal health [1]. An increasing incidence of tick-borne diseases has been reported world-wide in recent years, which constitutes a critical concern for public and animal health [2, 3]. Northward expansion of the geographic range of I. scapularis, from the United States into Eastern and Central Canada, is occurring and has resulted in an increased risk for Lyme disease in parts of southern Canada [10]. The ticks are thought to be mostly introduced into Canada by migratory birds moving north in the springtime [12]. Mammalian hosts, such as the white-tailed deer Odocoileus virginianus Zimmermann, likely play a role in dispersing ticks mostly over short distances to nearby habitats [13]. Ticks carried by dispersing hosts, as well as the reservoir-competent hosts themselves, may be infected with B. burgdorferi and introduce the bacterium to locations where tick populations have become established resulting in the emergence of new Lyme disease risk areas [14]
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