Ixodes (Ixodes) scapularis (Acari: Ixodidae): Redescription of all Active Stages, Distribution, Hosts, Geographical Variation, and Medical and Veterinary Importance

Abstract

The blacklegged tick, Ixodes (Ixodes) scapularis Say, 1821, is redescribed, based on laboratory reared specimens originating in Bulloch County, Georgia. Information on distribution, host associations, morphological variation, and medical/veterinary importance is also presented. A great deal of recent work has focused on this species because it is the principal vector of the agent of Lyme disease (Borrelia burgdorferi Johnson, Schmidt, Hyde, Steigerwaldt & Brenner) in eastern North America. Its distribution appears to be expanding, and includes the state of Florida in the southeastern United States north to the provinces of Nova Scotia and Prince Edward Island, Canada, west to North and South Dakota, United States, and south to the state of Coahuila, Mexico. Although I. scapularis feeds on at least 125 species of North American vertebrates (54 mammalian, 57 avian, and 14 lizard species), analysis of the U.S. National Tick Collection holdings show that white-tailed deer, Odocoileus virginianus (Zimmermann), cattle, Bos taurus L., dogs, Canis lupus L., and other medium-to-large sized mammals are important hosts for adults as are native mice and other small mammals, certain ground-frequenting birds, skinks, and glass lizards for nymphs and larvae. This tick is a polytypic species exhibiting north-south and east-west morphological clines. Analysis of variance and Student-Newman-Keuls multiple comparisons revealed significant interpopulational variation that is expressed most significantly in the nymphal stage. Nymphs from northern (Minnesota, Massachusetts, Maryland) populations had relatively larger basis capituli with shorter cornua (except Maryland) than southern (North Carolina, Georgia) populations. Midwestern populations (Minnesota, Missouri) differed from eastern populations (Massachusetts, Maryland, North Carolina, Georgia) in idiosomal characters (broader scuta, larger coxae III, and IV). In addition to Lyme disease, this tick is also a primary vector of the agent of human and rodent babesiosis, Babesia microti Franca. Under laboratory conditions it has transmitted the agents of deer babesiosis, Babesia odocoilei Emerson & Wright, tularemia, Francisella tularensis McCoy & Chapin, and anaplasmosis, Anaplasma marginale Theiler. Moreover, I. scapularis can reach pest proportions on livestock, and females can cause tick paralysis in dogs.

A climate-based model predicts the spatial distribution of the Lyme disease vector Ixodes scapularis in the United States.

“…Areas that are suitable but not currently sustained are those that will experience the greatest increase in I. scapularis population density, because introductions should result in reproducing populations. The presence of these areas validates the idea that I. scapularis continues to expand its range (Dennis et al 1998;Keirans et al 1996). According to the model, notable increases in vector distribution are expected in Virginia, North Carolina, Georgia, Minnesota, Iowa, and Michigan.…”

“…I. scapularis is the primary vector of Borrelia burgdorferi, the agent of Lyme disease, in North America (Dennis et al 1998;Keirans et al 1996). Lyme disease is currently the most prevalent vectorborne disease in the United States, with more than 100,000 cases reported by the U.S. Centers for Disease Control and Prevention since its discovery in 1982 (Orloski et al 2000).…”

Effect of Climate Change on Lyme Disease Risk in North America

“…This trend is clearly shown by the spreading of suitable area north into Canada. Though I. scapularis has been collected from a variety of locations in Canada (Keirans, Hutcheson et al 1996;Scott, Fernando et al 2001), establishment has only been shown for a limited number of locations in southern Ontario (Lindsay, Artsob et al 1998;Barker and Lindsay 2000). Climate change may provide the conditions necessary to yield reproducing populations of I. scapularis either by the systematic advancement from south of the border by movement on mammal hosts or by adventitious introductions from attachment to bird hosts (Klich, Lankester et al 1996).…”

“…The tick, Ixodes scapularis, the primary vector of Lyme disease in North America (Keirans, Hutcheson et al 1996;Dennis, Nekomoto et al 1998), is highly dependent on climate patterns (Stafford 1994;Lindsay, Barker et al 1995;Bertrand and Wilson 1996). The abiotic environment plays a vital role in the survival of I. scapularis with both water stress and temperature regulating off-host mortality (Needham and Teel 1991;Bertrand and Wilson 1996).…”

An ecological approach to preventing human infection: Vaccinating wild mouse reservoirs intervenes in the Lyme disease cycle

“…Larval I. scapularis are not host-specific and have been found to feed on many vertebrate species (17). On the basis of previous studies (18,19), we anticipated that the impact of vaccination on reducing nymphal infection prevalence would correlate positively with the proportional role that mice play in infecting larvae.…”