Invasion of the Lyme Disease Vector Ixodes scapularis: Implications for Borrelia burgdorferi Endemicity

Abstract

Lyme disease risk is increasing in the United States due in part to the spread of blacklegged ticks Ixodes scapularis, the principal vector of the spirochetal pathogen Borrelia burgdorferi. A 5-year study was undertaken to investigate hypothesized coinvasion of I. scapularis and B. burgdorferi in Lower Michigan. We tracked the spatial and temporal dynamics of the tick and spirochete using mammal, bird, and vegetation drag sampling at eight field sites along coastal and inland transects originating in a zone of recent I. scapularis establishment. We document northward invasion of these ticks along Michigan's west coast during the study period; this pattern was most evident in ticks removed from rodents. B. burgdorferi infection prevalences in I. scapularis sampled from vegetation in the invasion zone were 9.3% and 36.6% in nymphs and adults, respectively, with the majority of infection (95.1%) found at the most endemic site. There was no evidence of I. scapularis invasion along the inland transect; however, low-prevalence B. burgdorferi infection was detected in other tick species and in wildlife at inland sites, and at northern coastal sites in years before the arrival of I. scapularis. These infections suggest that cryptic B. burgdorferi transmission by other vector-competent tick species is occurring in the absence of I. scapularis. Other Borrelia spirochetes, including those that group with B. miyamotoi and B. andersonii, were present at a low prevalence within invading ticks and local wildlife. Reports of Lyme disease have increased significantly in the invasion zone in recent years. This rapid blacklegged tick invasion--measurable within 5 years--in combination with cryptic pathogen maintenance suggests a complex ecology of Lyme disease emergence in which wildlife sentinels can provide an early warning of disease emergence.

Human Granulocytic Anaplasmosis in the United States from 2008 to 2012: A Summary of National Surveillance Data

“…31 Similarly, increasing ranges for I. scapularis have been documented along the Hudson River Valley, Michigan, and Virginia. [32][33][34] Comparing the maps presented here with our previous surveillance summary from 2000 to 2007, anaplasmosis appears to be increasing in geographic range as well as in IR, consistent with changes in the range of its tick vector. 30 More cases were reported during 2008-2012 than during 2000-2007; and, analysis of human data in tandem with ecological data may elucidate changing risk of exposure to human populations.…”

Human Risk of Infection with Borrelia burgdorferi, the Lyme Disease Agent, in Eastern United States

“…Using this threshold, the final model had 91% accuracy, 93% sensitivity, and 90% specificity. The model predicted the presence of infected nymphs in some negative sites for which other sources indicate emerging risk, such as eastern Maine, 30 the Illinois/Indiana border, 24,31 the New York/Vermont border, 32 southwestern Michigan, 33 and eastern North Dakota (Vaughan J, personal communication). The density of infected nymphs was often underestimated by the model in these regions, and bootstrap CIs often included the threshold value for infected nymphs, therefore the sites could not be assigned to a 95% confidence risk category.…”

“…Uninfected I. scapularis populations were also identified along two of these putative expansion fronts (Illinois/Indiana and New York/Vermont), consistent with a pattern of initial tick spread followed by the spread of B. burgdorferi. 34 An alternative invasion pattern was detected in Michigan, 33 where low-prevalence B. burgdorferi infection was detected in other tick species and in wildlife at inland sites before the arrival of I. scapularis. The authors suggested a cryptic B. burgdorferi transmission cycle by other vectorcompetent tick species in the absence of I. scapularis.…”

Comparative Efficacy of an Imidacloprid/Flumethrin Collar (Seresto®) and an Oral Fluralaner Chewable Tablet (Bravecto®) against Tick (Dermacentor variabilis and Amblyomma americanum) Infestations on Dogs: a Randomised Controlled Trial

“…The myriad of tick species and wide variety of tick lifestyles makes them difficult to control in domestic animals, and their ability to survive adversity allows them to successfully follow their hosts into new and diverse habitats. Those traits, along with other factors such as habitat destruction, climate change, and pet portability, will likely increase encounters between ticks and pets in the future (Bacon et al 2008;Chomel 2011;Diuk-Wasser et al 2012;Hamer et al 2010). New information is continually being learned regarding tick-borne diseases in the medical and veterinary communities.…”