Range Expansion of Tick Disease Vectors in North America: Implications for Spread of Tick-Borne Disease

Abstract

Ticks are the major vectors of most disease-causing agents to humans, companion animals and wildlife. Moreover, ticks transmit a greater variety of pathogenic agents than any other blood-feeding arthropod. Ticks have been expanding their geographic ranges in recent decades largely due to climate change. Furthermore, tick populations in many areas of their past and even newly established localities have increased in abundance. These dynamic changes present new and increasing severe public health threats to humans, livestock and companion animals in areas where they were previously unknown or were considered to be of minor importance. Here in this review, the geographic status of four representative tick species are discussed in relation to these public health concerns, namely, the American dog tick, Dermacentor variabilis, the lone star tick, Amblyomma americanum, the Gulf Coast Tick, Amblyomma maculatum and the black-legged tick, Ixodes scapularis. Both biotic and abiotic factors that may influence future range expansion and successful colony formation in new habitats are discussed.

Keywords: Amblyomma americanum; Amblyomma maculatum; Dermacentor variabilis; Ixodes scapularis; abiotic factors; biotic factors; climate change; habitats; hosts.

Figure 1

Maps showing the average minimum January temperatures (°F) in the continental United States: (A) 1970; (B) 2016. Dark Blue = –10 °F; medium blue = 11–20 °F; light blue = 21–30 °F; blue-green = 31–40 °F; gray = 41–50 °F. Photo credits Dr. R. Ryan Lash, Traveler’s Health Branch, DGMQ, Centers for Disease Control and Prevention, Atlanta, GA.

Figure 2

Map showing the current versus the historic geographic distribution of the Gulf Coast Tick, Amblyomma maculatum (yellow distribution based on [24] and CDC map). Dark black line and the four isolated black dots indicate the historic distribution based on Bishop and Trembley [32]. Asterisks in southeastern Arizona indicate new established populations as reported by Allerdice et al. [26]. Photo credit Dr. R. Ryan Lash, Traveler’s Health Branch, DGMQ, Centers for Disease Control and Prevention, Atlanta, GA.