Emerging or re-emerging tick-borne pathogens are expected to increase in prevalence and become more geographically widespread in Canada. Borrelia burgdorferi, the bacterium causing Lyme disease, is the most common vector-borne pathogen in North America, but additional tick-borne pathogens have started to be detected more frequently through surveillance efforts in Canada. The spread and transmission of these tick-borne pathogens are modulated by changes in the abundance and distribution of tick and host populations. Abiotic factors, such as temperature, precipitation, and snow, may affect tick and host abundances as well as host dispersal. Furthermore, biotic factors, such as the abundance and diversity of hosts, may alter tick abundance and consequent tick-borne disease risk. In this dissertation, I assess the historical associations and spatiotemporal changes of the tick vectors, hosts, and pathogens in Canada as well as the impact of abiotic and biotic factors on these key players.
In Chapter 1, I present the first systematic assessment of the literature that identifies historical associations and spatiotemporal changes in the tick-host-pathogen disease systems in Canada over broad spatial and temporal scales. Borrelia burgdorferi was the most detected tick-borne pathogen and Ixodes scapularis harboured the greatest number of tick-borne pathogens. Several spatial outliers of high pathogen presence in ticks in addition to five spatiotemporal clusters were identified, which were located in areas of southern Canada with long-established tick populations. In addition, six spatiotemporal clusters of high pathogen presence were also identified, with four clusters associated with passive surveillance and two clusters related to active surveillance.
In chapter 2, I concurrently evaluated high-resolution environmental and host-related factors to determine the relative impacts of abiotic and biotic factors on questing I. scapularis abundance in Ontario and Quebec. High-resolution abiotic factors were derived from remote sensing satellite imagery and meteorological towers, while biotic factors related to mammal hosts were derived from active surveillance data that I collected in the field. Important abiotic and biotic drivers of questing I. scapularis abundance were identified, which included monthly mean precipitation, accumulated snow, and mammal species richness. These results demonstrate the need to incorporate host active surveillance data with high-resolution environmental factors when trying to determine the key drivers impacting the abundance and distribution of tick populations and tick-borne pathogens.
In Chapter 3, I analyzed the presence and prevalence of multiple tick-borne pathogens extracted from tick and small mammal specimens collected during field surveys in Ontario and Quebec. Three pathogen species were detected in ticks, which included Babesia odocoilei and B. burgdorferi in I. scapularis as well as Rickettsia rickettsii in Haemaphysalis leporispalustris. In small mammal hosts, three pathogen species were detected including B. odocoilei in one shrew, B. microti in one deer mouse, and Hepatozoon in one deer mouse and one white-footed mouse. My findings provide evidence that emerging or re-emerging tick-borne pathogens may be present outside currently defined risk areas identified by surveillance efforts in Canada.
Finally, in chapter 4, I examined the effect of biotic factors related to I. scapularis and mammal hosts on the presence, prevalence, and diversity of pathogens in Ontario and Quebec using data from field surveys. Local infection prevalence ranged from 0% to 25.4% in questing ticks and from 0% to 16.7% in small mammal hosts. Local pathogen presence and prevalence were not impacted by I. scapularis abundance nor the abundance and diversity of mammal hosts. However, mammal species richness was a key predictor of the number of pathogen species.
Collectively, my dissertation provides insight into the historical and contemporary relationships between ticks, hosts, and pathogens in Canada. My results demonstrate that additional tick species such as H. leporispalustris may be of public health importance due to their ability to maintain pathogens within the environment without needing a host. In addition, certain emerging or re-emerging tick-borne pathogens, such as B. odocoilei and R. rickettsii, were detected outside of currently defined risk areas in southeastern Quebec, which may impact future surveillance efforts in these regions. Furthermore, this work highlights the need for proactive and comprehensive surveillance efforts that test questing and feeding ticks of all life stages and species, as well as their hosts in areas outside currently defined risk areas or those targeted by sentinel surveillance to better determine the spread, transmission, and co-occurrence of tick-borne pathogens in Canada.
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/45760 |
| Date | 20 December 2023 |
| Creators | Crandall, Kirsten |
| Contributors | Kerr, Jeremy T., Millien, Virginie |
| Publisher | Université d'Ottawa / University of Ottawa |
| Source Sets | Université d’Ottawa |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
Page generated in 0.0023 seconds