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Ixodes scapularis

Ixodes scapularis
Community contact: 
Catherine Hill

Ixodes scapularis, Black-legged tick, is a hard-bodied tick from the Ixodidae family. Ix. scapularis is the primary vector for Lyme disease transmitting the pathogenic bacterium Borrelia burgdorfei.

Ixodes ticks also can transmit Ehrlichia, a gram-negative obligate intracellular bacteria that is responsible for Ehrlichiosis.

Ticks that transmit Borrelia burgdorferi to humans can also carry and transmit several other parasites, such as Theileria microti and Anaplasma phagocytophilum, which cause the diseases babesiosis and human granulocytic anaplasmosis, respectively.

From Wikipedia: Ixodes scapularis is commonly known as the deer tick or blacklegged tick (although some people reserve the latter term for Ixodes pacificus, which is found on the West Coast of the USA), and in some parts of the USA as the bear tick. It is a hard-bodied tick (family Ixodidae) of the eastern and northern Midwestern United States. It is a vector for several diseases of animals, including humans (Lyme disease, babesiosis, anaplasmosis, etc) and is known as the deer tick due to its habit of parasitizing the white-tailed deer.

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Genome analysis of major tick and mite vectors of human pathogens

Ticks and mites (subphylum Chelicerata: class Acari) transmit a greater variety of human and animal pathogens than any other arthropod vector. Tick- and mite-borne diseases are global health problems caused by a variety of bacterial, viral and protozoan pathogens, which are responsible for significant morbidity and thousands of human deaths annually. The incidence of many tick-borne diseases is increasing worldwide - many are emerging zoonoses or exotic diseases that could be introduced to the U.S. The Acari are a diverse and basal group within the phylum Arthropoda, comprised of two lineages; the Acariformes or chigger mites and the Parasitiformes which includes the ticks (suborder Ixodida) and other medically important mites. Despite their impact on human health, little is known about the biology and genetic basis of vector competence in the Acari. The NIH funded Ixodes scapularis (Lyme disease tick) assembly represents the only available genome sequence of a medically important species within this entire diverse lineage. Unfortunately, application of this resource is limited by low sequence coverage and fragmentation of the assembly.

Here we propose immediate sequencing of the mite vector of scrub typhus, Leptotrombidium deliense, and additional sequencing of I. scapularis to expand genomic resources for this group (summarized in Table 1). These projects will provide the anchor for additional sampling of species at increasing evolutionary distance. We also identify six members of the Ixodida (Dermacentor variabilis, Amblyomma americanum, I. pacificus, I. ricinus, I. persulcatus and Ornithodorus turicata) that are considered high priority sequencing targets by the tick and mite research communities. The haploid genome size of these ticks is expected to exceed 1 Gbp. Recognizing the inherent challenges associated with de novo sequencing and assembly of such genomes and the likely rapid advances anticipated in genome sequencing and assembly technology, we propose extensive transcriptome sequencing of these species to position them for anticipated genome sequencing efforts. Should sequencing of L. deliense and I. scapularis prove successful, we identify two additional species of Ixodida (D. variabilis and O. turicata) as candidates for genome sequencing efforts.

Identifying new strategies to control tick and mite vectors and the pathogens they transmit is a central theme of tick and mite research programs worldwide. The genome sequence data needed to accomplish these goals are not yet in hand. This proposal represents the cooperative efforts of the international tick and mite research community to develop the critical resources to facilitate comprehensive genomic studies across this important, yet largely neglected group of arthropod vectors. It outlines our long term plan for implementing genomic research in major evolutionary groups and key vector species of the Acari, and identifies the steps the community will take to achieve this goal.

Cate A. Hill, Tick and Mite Genomes Consortium
Broad Institute
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Ixodes scapularis
Leptotrombidium deliense
Dermacentor variabilis
Ornithodoros turicata


The annotation of the Ixodes genome is a collaboration between VectorBase, JCVI with support from the Broad Institute. Each group generated a set of gene predictions which were merged into a single canonical set (IscaW1.1). The merging strategy will be described in the genome paper (in preparation).

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Release date: 
Monday, December 1, 2008


The Ixodes scapularis Wikel strain genome sequence is a joint effort between the Broad Institute and the J. Craig Venter Institute (JCVI).

Gene Count: 
24 925
Protein-coding gene count: 
20 486
Other gene count: 
4 439
Transcript count: 
24 925
Protein-coding transcript count: 
20 486
Other transcript count: 
4 439
Manually reviewed genes: 
Genes updated by VB users: 
Peptide Count: 
20 486
Exon Count: 
93 988
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Total gene updates: 


The Ixodes scapularis Wikel colony was established by Dr. S. Wikel (University of Connecticut Health Center) in 1996 using approximately 30 pairs of field collected adult male and female ticks from New York, Oklahoma and a Lyme disease endemic area of Connecticut. The colony has been continuously in-bred for approximatley twelve generations since establishment and has not been supplemented with field collected material. The colony is known to be a competent vector of various Borrelia burgdorferi (strains B31 and 297) and Babesia microti isolates. Dr. D. Sonenshine at Old Dominion University also maintains a satellite colony of the Wikel strain.

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