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.
Reciprocal crosses between Ixodes dammini Spielman, Clifford, Piesman & Corwin from Massachusetts and Ixodes scapularis Say from Georgia produced offspring through the F3 generation when the experiment was discontinued. Reciprocal I. dammini x Ixodes pacificus Cooley & Kohls (California) and I. scapularis x I. pacificus crosses produced F1 progeny; however, all progeny were sterile. Assortative mating experiments between I. dammini and I. scapularis indicated that males and females of both species mated with the opposite sex of heterospecific or conspecific ticks when there was a choice. Conventional discriminant analysis of morphometric measurements of ticks from Georgia, North Carolina, Maryland, Massachusetts, and two populations of F1 hybrids indicated that there were recognizable differences. However, size-free (sheared) discriminant analysis indicated that these differences were largely size-dependent, with much overlap of the four eastern and two hybrid populations but no overlap with I. pacificus from California. Analysis of chromosomes (morphology and C band) indicated no differences between the Georgia and Massachusetts populations but showed a difference between them and the California population of I. pacificus. Analysis of isozymes showed that the genetic identity value for the Georgia and Massachusetts populations was within the normal range for conspecific populations, whereas the California population indicated congeneric but not conspecific relatedness to the Georgia and Massachusetts populations. Life cycle data collected under similar laboratory conditions showed no differences in length of feeding and molting periods among Georgia, Massachusetts, and California populations. These data and results of the work of other authors on tick host preferences and vector competence indicate that I. dammini is not a valid species separate from I. scapularis. Because the name Ixodes scapularis Say, 1821, has priority over the name Ixodes dammini Spielman, Clifford, Piesman & Corwin, 1979, I. dammini is relegated to a junior subjective synonym of I. scapularis (based on Article 23 of the International Code of Zoological Nomenclature).
We report an outbreak of equine piroplasmosis in southern Texas, USA, in 2009. Infection prevalence reached 100% in some areas (292 infected horses). Amblyomma cajennense was the predominant tick and experimentally transmitted Theileria equi to an uninfected horse. We suggest that transmission by this tick species played a role in this outbreak.
The isolation of the Lyme disease spirochete (Borrelia burgdorferi) from the southeastern United States is reported. Three isolates, two from cotton mice (Peromyscus gossypinus) and one from the black-legged tick (Ixodes scapularis), were recovered from Sapelo Island, Georgia, in July and September 1991. The spirochetes were characterized by indirect fluorescent antibody assay using a battery of five monoclonal antibodies, by sodium dodecyl sulfate/polyacrylamide gel electrophoresis (SDS/PAGE) of whole cell lysates, and by the polymerase chain reaction (PCR) assay using primers for three DNA target sequences found in B. techniques (20). Before culturing, mouse ears were cleaned with 95% ethanol and ear clips were sliced into small pieces or several 2-mm punches were taken from each ear. Ear clips or punches were cleaned again in 95% ethanol followed by a rinse in a 1:1 mixture of 10% Clorox and 95% ethanol. Ear punches were then placed into 1.25 ml BSK II medium (18) and small ear slices were placed in 4.5 ml of medium. All cultures were incubated in a 5% CO2 atmosphere at 33-34°C and examined for spirochetes by darkfield microscopy twice weekly for 2 weeks and, if spirochetes were not detected, weekly thereafter for 6 weeks. Spirochetal isolates were tested by indirect fluorescent antibody analysis (21, 22) using five monoclonal antibodies, including two B. burgdorferi-specific anti-outer surface protein A (OspA) monoclonals (H3TS and H5332), two B. burgdorferi-specific anti-outer surface protein B (OspB) monoclonals (HSTS and H6831), and a Borrelia (genus)-specific anti-flagellin monoclonal antibody (H9724).Preparation ofeach spirochetal culture for characterization by sodium dodecyl sulfate/polyacrylamide gel electrophoresis (SDS/PAGE) involved whole spirochetal lysates (23, 24). Aliquots of 20 ml each were centrifuged at 10,000 x g for 30 min. Supernatants were removed and spirochetal pellets were suspended in 1 ml of phosphate-buffered saline (PBS: 120 mM NaCl/2.7 mM KCl/10 mM Na2HPO4/10 mM KH2PO4, pH 7.4) with 5 mM MgCl2 by vortex mixing until evenly dispersed. Samples were centrifuged again at 10,000 x g for 15 min. After a second PBS/MgC12 wash, spirochetal pellets were resuspended in 0.1 ml of sterile distilled water and then frozen at -80°C for 30 min, thawed, and refrozen. After the final thaw, the suspended spirochetal pellets were vortex-mixed and an aliquot was then removed for total Abbreviation: LD, Lyme disease.tTo whom correspondence should be addressed. 7371
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