''Ixodes scapularis'' is a hard-bodied

tick Ticks are parasitic arachnids of the order Ixodida. They are part of the mite superorder Parasitiformes. Adult ticks are approximately 3 to 5 mm in length depending on age, sex, and species, but can become larger when engorged. Ticks a ...

found in much of the eastern half of North America. It is commonly known as the deer tick, owing to its habit of parasitizing the

white-tailed deer The white-tailed deer (''Odocoileus virginianus''), also known Common name, commonly as the whitetail and the Virginia deer, is a medium-sized species of deer native to North America, North, Central America, Central and South America. It is the ...

. It is also sometimes known as the black-legged tick (although some people reserve that specific term for '' Ixodes pacificus'', which is found on the west coast of the US), and as the bear tick in some parts of the US. It was also named ''Ixodes dammini'' until it was shown to be the same species in 1993. It is a

vector Vector most often refers to: * Euclidean vector, a quantity with a magnitude and a direction * Disease vector, an agent that carries and transmits an infectious pathogen into another living organism Vector may also refer to: Mathematics a ...

for several diseases of animals, including humans (

Lyme disease Lyme disease, also known as Lyme borreliosis, is a tick-borne disease caused by species of ''Borrelia'' bacteria, Disease vector, transmitted by blood-feeding ticks in the genus ''Ixodes''. It is the most common disease spread by ticks in th ...

babesiosis Babesiosis or piroplasmosis is a malaria-like parasitic disease caused by infection with a eukaryotic parasite in the order Piroplasmida, typically a ''Babesia'' or '' Theileria'', in the phylum Apicomplexa. Human babesiosis transmission via ...

anaplasmosis Anaplasmosis is a tick-borne disease affecting ruminants, dogs, and horses, and is caused by ''Anaplasma'' bacteria. Anaplasmosis is an infectious but not contagious disease. Anaplasmosis can be transmitted through mechanical and biological vector ...

, Powassan virus disease, etc.). It is also known to parasitize mice, lizards, migratory birds, etc. especially while the tick is in the larval or nymphal stage.

Description

As a nymph and adult, ''Ixodes scapularis'' has eight legs, while larvae have six. Unlike ticks from other genera, deer ticks do not have eyes. The scutum is dark, inornate (plain), and, in unfed females, contrasts with the exposed orange or red remainder of the idiosoma. There are no

festoon A festoon (from French ''feston'', Italian ''festone'', from a Late Latin ''festo'', originally a festal garland, Latin ''festum'', feast) is a wreath or garland hanging from two points, and in architecture typically a carved ornament depicti ...

s. ''Ixodes'' ticks have an anal groove that resembles a horseshoe on their underside anterior to the anal pore. The palps of male deer ticks, part of the mouthparts or capitulum, are shorter than those of the female. Adult female deer ticks are approximately 3 to 4 mm long, and may engorge while feeding, while adult males are 2 to 3 mm long and cannot engorge due to the rigidity of their scutum, which covers the entire male body.

Behavior

''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. After she is engorged, the tick drops off and overwinters in the

leaf litter Plant litter (also leaf litter, tree litter, soil litter, litterfall, or duff) is dead plant material (such as leaves, bark, needles, twigs, and cladodes) that has fallen to the ground. This detritus or dead organic material and its constituen ...

of the

forest floor The forest floor, also called detritus or wikt:duff#Noun 2, duff, is the part of a forest ecosystem that mediates between the living, aboveground portion of the forest and the mineral soil, principally composed of dead and decaying plant matter ...

. The following spring, the female lays several hundred to a few thousand eggs in clusters. Transtadial (between tick stages) passage of ''

Borrelia burgdorferi ''Borrelia burgdorferi'' is a bacterial species of the spirochete class in the genus '' Borrelia'', and is one of the causative agents of Lyme disease in humans. Along with a few similar genospecies, some of which also cause Lyme disease, it m ...

'' is common. Vertical passage (from mother to egg) of ''Borrelia'' is uncommon. Like other ticks, ''I. scapularis'' is hardy. It can be active after a hard

frost Frost is a thin layer of ice on a solid surface, which forms from water vapor that deposits onto a freezing surface. Frost forms when the air contains more water vapor than it can normally hold at a specific temperature. The process is simila ...

, as daytime temperatures can warm it enough to keep it actively searching for a host. In the spring, it can be one of the first

invertebrate Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordata, chordate s ...

s to become active. Deer ticks can be quite numerous and seemingly

gregarious Sociality is the degree to which individuals in an animal population tend to associate in social groups (gregariousness) and form cooperative societies. Sociality is a survival response to evolutionary pressures. For example, when a mother was ...

As disease vector

''Ixodes scapularis'' is the main

in North America. 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. While adult deer ticks are more likely to carry and transmit ''Borrelia burgdorferi'', it is more common for the hard-to-spot nymphal stage to infect humans. It can also transmit other ''Borrelia'' species, including '' Borrelia miyamotoi''. Ticks that transmit '' B. burgdorferi'' to humans can also carry and transmit several other parasites, such as '' Babesia microti'' and ''

Anaplasma phagocytophilum ''Anaplasma phagocytophilum'' (formerly ''Ehrlichia phagocytophilum'') is a Gram-negative bacterium that is unusual in its tropism to neutrophils. It causes anaplasmosis in sheep and cattle, also known as tick-borne fever and pasture fever, an ...

'', which cause the diseases

and human granulocytic anaplasmosis (HGA), respectively. Among early Lyme disease patients, depending on their location, 2%–12% will also have HGA and 2%–40% will have babesiosis. 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 not ''Borrelia'', making diagnosis difficult and often elusive. The

Centers for Disease Control The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency under the Department of Health and Human Services (HHS), and is headquartered in Atlanta, ...

'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. Deer, the preferred mammalian hosts of adult ''I. scapularis'', cannot transmit ''Borrelia'' spirochaetes to ticks. Ticks acquire Lyme disease microbes by feeding on infected

mice A mouse (: mice) is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse (''Mus musculus' ...

and other small rodents as nymphs or larvae. One of the keys of the success of ''I. scapularis'' as a ''Borrelia'' 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 of horizontally 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; 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. The product of dae2 expression has been shown to degrade bacterial peptidoglycan of different species and particularly from ''B. burgdorferi'', but does not limit initial acquisition of the bacterium by the tick. Dae2 contributes to the innate ability of ''I. scapularis'' to control '' B. burgdorferi'' levels after its acquisition. This has potential ramifications for Lyme disease transmission, as spirochaete load in the tick can influence transmission efficiency. A recent study has identified the alpha-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).

Genome sequencing

The genome of ''I. scapularis'' has been sequenced.''Ixodes scapularis'' genome sequence at VectorBase
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References

External links