Geography, Deer, and Host Biodiversity Shape the Pattern of Lyme Disease Emergence in the Thousand Islands Archipelago of Ontario, Canada

Abstract

In the Thousand Islands region of eastern Ontario, Canada, Lyme disease is emerging as a serious health risk. The factors that influence Lyme disease risk, as measured by the number of blacklegged tick (Ixodes scapularis) vectors infected with Borrelia burgdorferi, are complex and vary across eastern North America. Despite study sites in the Thousand Islands being in close geographic proximity, host communities differed and both the abundance of ticks and the prevalence of B. burgdorferi infection in them varied among sites. Using this archipelago in a natural experiment, we examined the relative importance of various biotic and abiotic factors, including air temperature, vegetation, and host communities on Lyme disease risk in this zone of recent invasion. Deer abundance and temperature at ground level were positively associated with tick abundance, whereas the number of ticks in the environment, the prevalence of B. burgdorferi infection, and the number of infected nymphs all decreased with increasing distance from the United States, the presumed source of this new endemic population of ticks. Higher species richness was associated with a lower number of infected nymphs. However, the relative abundance of Peromyscus leucopus was an important factor in modulating the effects of species richness such that high biodiversity did not always reduce the number of nymphs or the prevalence of B. burgdorferi infection. Our study is one of the first to consider the interaction between the relative abundance of small mammal hosts and species richness in the analysis of the effects of biodiversity on disease risk, providing validation for theoretical models showing both dilution and amplification effects. Insights into the B. burgdorferi transmission cycle in this zone of recent invasion will also help in devising management strategies as this important vector-borne disease expands its range in North America.

Analyzing the Potential Risk of Climate Change on Lyme Disease in Eastern Ontario, Canada Using Time Series Remotely Sensed Temperature Data and Tick Population Modelling

“…Much of the current research on Lyme disease risk mapping is focused on finding factors that correlate well with current tick presence [32], or projecting future tick habitat distribution due to climate change [2,33]. This study examined whether there is evidence that the geographic distribution of Lyme disease risk in eastern Ontario has changed between 2000 and 2013 due to climate change, where the capacity to sustain an endemic tick population was used as a proxy for Lyme disease risk.…”

“…Several of these factors have been previously studied, in terms of how they correlate with I. scapularis presence. For instance, in the Thousand Islands region, Ontario, host-species abundance was found to be strongly positively correlated with tick abundance, while species richness, a measure of biodiversity, is inversely associated [32]. Also, in the eastern United States, altitude and monthly mean vapour pressure were found to be predictors of tick density [38].…”

Evidence for Personal Protective Measures to Reduce Human Contact With Blacklegged Ticks and for Environmentally Based Control Methods to Suppress Host-Seeking Blacklegged Ticks and Reduce Infection with Lyme Disease Spirochetes in Tick Vectors and Rodent Reservoirs

“…Field evidence rather show that deer density is positively associated with both numbers of I. scapularis immatures infesting rodent reservoirs (Wilson et al 1985, 1988, 1990; Deblinger et al 1993; Rand et al 1994; Stafford et al 2003) and abundance of host-seeking B. burgdorferi -infected nymphs (Kilpatrick et al 2014, Werden et al 2014). …”

The Biological Survey of Canada: A Personal History

“…It appears that established populations of tick vectors and natural endemic cycles of B. burgdorferi have a limited but expanding geographic scope in Canada, accounting for the relatively low reported incidence of Lyme borreliosis in Canada compared to the United States of America. Established populations of B. burgdorferi-infected I. scapularis have been identified in a number of locations in Ontario, including at Long Point peninsula on the north shore of Lake Erie, Point Pelee National Park and Rondeau and Turkey Point Provincial Parks, around Lake Ontario in the vicinity of the Thousand Islands National Park (Werden et al 2014) and tick populations appear to be moving inland in much of eastern Ontario (Nelder et al 2014). Established populations of infected I. scapularis have also been detected in parts of Québec, Nova Scotia, New Brunswick, and southern Manitoba (http:// www.phac-aspc.gc.ca/id-mi/tickinfo-eng.php).…”