| Ixodes scapularis | |
|---|---|
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| Adult female deer tick | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Subphylum: | Chelicerata |
| Class: | Arachnida |
| Order: | Ixodida |
| Family: | Ixodidae |
| Genus: | Ixodes |
| Species: | I. scapularis |
| Binomial name | |
| Ixodes scapularis Say, 1821 | |
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| Synonyms[1] | |
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Ixodes scapularis is a hard-bodiedtick found in much of the eastern half of North America. It is commonly known as thedeer tick, owing to its habit ofparasitizing thewhite-tailed deer. It is also sometimes known as theblack-legged tick (although some people reserve that specific term forIxodes pacificus, which is found on the west coast of the US), and as thebear tick in some parts of the US.[2] It was also namedIxodes dammini until it was shown to be the same species in 1993.[3]
It is avector for several diseases of animals, including humans (Lyme disease,babesiosis,anaplasmosis,Powassan virus disease, etc.). It is also known to parasitize mice,[4] lizards,[5] migratory birds,[6] etc. especially while the tick is in the larval or nymphal stage.
As a nymph and adult,Ixodes scapularis has eight legs, while larvae have six.[7] Unlike ticks from other genera,[8] deer ticks do not have eyes.[3][8] The scutum is dark, inornate (plain), and, in unfed females, contrasts with the exposed orange or red remainder of theidiosoma.[3] There are nofestoons.[3][9]Ixodes ticks have an anal groove that resembles a horseshoe[9] on their underside anterior to the anal pore.[8][10] The palps of male deer ticks, part of the mouthparts orcapitulum, are shorter than those of the female.[7][11]: 5 Adult female deer ticks are approximately 3 to 4 mm long,[10] and may engorge while feeding,[7] while adult males are 2 to 3 mm long[10] and cannot engorge due to the rigidity of their scutum, which covers the entire male body.[7]
Ixodes scapularis has a 2-year life cycle, during which time it passes through three stages: larva, nymph, and adult. The tick must take a blood meal at each stage before maturing to the next. Deer tick females latch onto a host and drink its blood for 4–5 days. Deer are the preferred host of the adult deer tick, but it is also known to feed on small rodents.[12] After she is engorged, the tick drops off andoverwinters in theleaf litter of theforest floor. The following spring, the female lays several hundred to a few thousand eggs in clusters.[13] Transtadial (between tick stages) passage ofBorrelia burgdorferi is common. Vertical passage (from mother to egg) ofBorrelia is uncommon.[citation needed]
Like other ticks,I. scapularis is hardy. It can be active after a hardfrost, as daytime temperatures can warm it enough to keep it actively searching for a host. In the spring, it can be one of the firstinvertebrates to become active. Deer ticks can be quite numerous and seeminglygregarious.[citation needed]
Ixodes scapularis is the mainvector ofLyme disease in North America.[14] The CDC reported over 30,000 new cases of the disease in 2016 alone, the majority of which were contracted in the summer months, which is when ticks are most likely to bite humans.[15] While adult deer ticks are more likely to carry and transmitBorrelia burgdorferi, it is more common for the hard-to-spot nymphal stage to infect humans.[16]
It can also transmit otherBorrelia species, includingBorrelia miyamotoi.[17] Ticks that transmitB. burgdorferi to humans can also carry and transmit several other parasites, such asBabesia microti andAnaplasma phagocytophilum, which cause the diseasesbabesiosis andhuman granulocytic anaplasmosis (HGA), respectively.[18] Among early Lyme disease patients, depending on their location, 2%–12% will also have HGA and 2%–40% will have babesiosis.[19]
Co-infections complicate Lyme symptoms, especially diagnosis and treatment. It is possible for a tick to carry and transmit one of the co-infections and notBorrelia, making diagnosis difficult and often elusive. TheCenters for Disease Control's emerging infectious diseases department did a study in rural New Jersey of 100 ticks, and found 55% of the ticks were infected with at least one of the pathogens.[20]
Deer, the preferred mammalian hosts of adultI. scapularis, cannot transmitBorreliaspirochaetes to ticks. Ticks acquire Lyme disease microbes by feeding on infectedmice and other small rodents as nymphs or larvae.[12]
One of the keys of the success ofI. scapularis as aBorrelia vector relies on its ability to limit the proliferation of the spirochaete. This is due to the activity of domesticated amidase effector (dae) genes. Dae genes are a family ofhorizontally acquired genes related to type VI secretion amidase effector (tae) genes in certain bacteria which encode toxins honed to mediate interbacterial antagonism. Once transferred to eukaryotes tae genes confer novel antibacterial capabilities;[21] this provides a selective advantage to the tick and to other eukaryotes also: tae genes have been transferred from bacteria to eukaryotes at least in six independent events. In particular,I. scapularis have inherited the dae 2 family from a common ancestor between ticks and mites.[21] The product of dae2 expression has been shown to degrade bacterial peptidoglycan of different species and particularly fromB. burgdorferi, but does not limit initial acquisition of the bacterium by the tick. Dae2 contributes to the innate ability ofI. scapularis to controlB. burgdorferi levels after its acquisition. This has potential ramifications for Lyme disease transmission, as spirochaete load in the tick can influence transmission efficiency.[21][22]
A recent study has identified thealpha-gal sugar in the tick, and they have suggested that it may also be involved in the onset of red meat allergy (Alpha-Gal Syndrome or Mammalian Meat Allergy, MMA).[23]
| NCBI ID | 6945 |
|---|---|
| Ploidy | diploid |
| Genome size | 1,765.38 Mb |
| Number ofchromosomes | 15 pairs |
| Year of completion | 2008 |
The genome ofI. scapularis has been sequenced.[24]
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| Other | |
