Ixodes scapularis | |
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Adult female deer tick | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Arthropoda |
Subphylum: | Chelicerata |
Class: | Arachnida |
Order: | Ixodida |
Family: | Ixodidae |
Genus: | Ixodes |
Species: | I. scapularis |
Binomial name | |
Ixodes scapularis Say, 1821 | |
Synonyms [1] | |
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Ixodes scapularis is commonly known as the deer tick or black-legged tick (although some people reserve the latter term for Ixodes pacificus , which is found on the west coast of the US), and in some parts of the US as the bear tick. [2] It was also named Ixodes dammini until it was shown to be the same species in 1993. [3] It is a hard-bodied tick found in the eastern and northern Midwest of the United States as well as in southeastern Canada. It is a vector for several diseases of animals, including humans (Lyme disease, babesiosis, anaplasmosis, Powassan virus disease, etc.) and is known as the deer tick owing to its habit of parasitizing the white-tailed deer. 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 the idiosoma. [3] There are no festoons. [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 or capitulum, 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 and overwinters in the leaf litter of the forest floor. The following spring, the female lays several hundred to a few thousand eggs in clusters. [13] Transtadial (between tick stages) passage of Borrelia burgdorferi is common. Vertical passage (from mother to egg) of Borrelia is uncommon.[ citation needed ]
Like other ticks, I. scapularis is hardy. It can be active after a hard frost, 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 invertebrates to become active. Deer ticks can be quite numerous and seemingly gregarious.[ citation needed ]
Ixodes scapularis is the main vector of Lyme 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 transmit Borrelia burgdorferi, it is more common for the hard-to-spot nymphal stage to infect humans. [16]
It can also transmit other Borrelia species, including Borrelia miyamotoi . [17] Ticks that transmit B. burgdorferi to humans can also carry and transmit several other parasites, such as Babesia microti and Anaplasma phagocytophilum , which cause the diseases babesiosis and human 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 not Borrelia, making diagnosis difficult and often elusive. The Centers 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 adult I. scapularis, cannot transmit Borrelia spirochaetes to ticks. Ticks acquire Lyme disease microbes by feeding on infected mice and other small rodents as nymphs or larvae. [12]
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; [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 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. [21] [22]
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). [23]
NCBI genome ID | 523 |
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Ploidy | diploid |
Genome size | 1,765.38 Mb |
Number of chromosomes | 15 pairs |
Year of completion | 2008 |
The genome of I. scapularis has been sequenced. [24]
Lyme disease, also known as Lyme borreliosis, is a tick-borne disease caused by species of Borrelia bacteria, transmitted by blood-feeding ticks in the genus Ixodes. The most common sign of infection is an expanding red rash, known as erythema migrans (EM), which appears at the site of the tick bite about a week afterwards. The rash is typically neither itchy nor painful. Approximately 70–80% of infected people develop a rash. Early diagnosis can be difficult. Other early symptoms may include fever, headaches and tiredness. If untreated, symptoms may include loss of the ability to move one or both sides of the face, joint pains, severe headaches with neck stiffness or heart palpitations. Months to years later, repeated episodes of joint pain and swelling may occur. Occasionally, shooting pains or tingling in the arms and legs may develop.
Tick-borne diseases, which afflict humans and other animals, are caused by infectious agents transmitted by tick bites. They are caused by infection with a variety of pathogens, including rickettsia and other types of bacteria, viruses, and protozoa. The economic impact of tick-borne diseases is considered to be substantial in humans, and tick-borne diseases are estimated to affect ~80 % of cattle worldwide. Most of these pathogens require passage through vertebrate hosts as part of their life cycle. Tick-borne infections in humans, farm animals, and companion animals are primarily associated with wildlife animal reservoirs. Many tick-borne infections in humans involve a complex cycle between wildlife animal reservoirs and tick vectors. The survival and transmission of these tick-borne viruses are closely linked to their interactions with tick vectors and host cells. These viruses are classified into different families, including Asfarviridae, Reoviridae, Rhabdoviridae, Orthomyxoviridae, Bunyaviridae, and Flaviviridae.
Borrelia burgdorferi is a gram-negative 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 makes up the species complex of Borrelia burgdorferi sensu lato. The complex currently comprises 20 accepted and 3 proposed genospecies. B. burgdorferi sensu stricto exists in North America and Eurasia and until 2016 was the only known cause of Lyme disease in North America.
The white-footed mouse is a rodent native to North America from southern Canada to the southwestern United States and Mexico. In the Maritimes, its only location is a disjunct population in southern Nova Scotia. It is also known as the woodmouse, particularly in Texas.
Ixodes holocyclus, commonly known as the Australian paralysis tick, is one of about 75 species in the Australian tick fauna and is considered the most medically important. It can cause paralysis by injecting neurotoxins into its host. It is usually found in a 20-kilometre wide band following the eastern coastline of Australia. Within that range, Ixodes holocyclus is the tick most frequently encountered by humans and their pets. Because the same area includes Australia's most densely populated regions, bites on people, pets and livestock are relatively common.
Dermacentor variabilis, also known as the American dog tick or wood tick, is a species of tick that is known to carry bacteria responsible for several diseases in humans, including Rocky Mountain spotted fever and tularemia. It is one of the best-known hard ticks. Diseases are spread when it sucks blood from the host. It may take several days for the host to experience symptoms.
Borrelia is a genus of bacteria of the spirochete phylum. Several species cause Lyme disease, also called Lyme borreliosis, a zoonotic, vector-borne disease transmitted by ticks. Other species of Borrelia cause relapsing fever, and are transmitted by ticks or lice, depending on the species of bacteria. A few Borrelia species as Candidatus Borrelia mahuryensis harbor intermediate genetic features between Lyme disease and relapsing fever Borrelia. The genus is named after French biologist Amédée Borrel (1867–1936), who first documented the distinction between a species of Borrelia, B. anserina, and the other known type of spirochete at the time, Treponema pallidum. This bacterium must be viewed using dark-field microscopy, which make the cells appear white against a dark background. Borrelia species are grown in Barbour-Stoenner-Kelly medium. Of 52 known species of Borrelia, 20 are members of the Lyme disease group, 29 belong to the relapsing fever group, and two are members of a genetically distinct third group typically found in reptiles. A proposal has been made to split the Lyme disease group based on genetic diversity and move them to their own genus, Borelliella, but this change is not widely accepted. This bacterium uses hard and soft ticks and lice as vectors. Testing for the presence of the bacteria in a human includes two-tiered serological testing, including immunoassays and immunoblotting.
Babesia, also called Nuttallia, is an apicomplexan parasite that infects red blood cells and is transmitted by ticks. Originally discovered by the Romanian bacteriologist Victor Babeș in 1888, over 100 species of Babesia have since been identified.
Powassan virus (POWV) is a Flavivirus transmitted by ticks, found in North America and in the Russian Far East. It is named after the town of Powassan, Ontario, where it was identified in a young boy who eventually died from it. It can cause encephalitis, inflammation of the brain. No approved vaccine or antiviral drug exists. Prevention of tick bites is the best precaution.
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 processes. Anaplasmosis can also be referred to as "yellow bag" or "yellow fever" because the infected animal can develop a jaundiced look. Other signs of infection include weight loss, diarrhea, paleness of the skin, aggressive behavior, and high fever.
Lyme disease, or borreliosis, is caused by spirochetal bacteria from the genus Borrelia, which has 52 known species. Three species are the main causative agents of the disease in humans, while a number of others have been implicated as possibly pathogenic. Borrelia species in the species complex known to cause Lyme disease are collectively called Borrelia burgdorferisensu lato (s.l.), not to be confused with the single species Borrelia burgdorferi sensu stricto, a member of the complex, which is responsible for nearly all cases of Lyme disease in North America.
Andrew Spielman was a prominent American public health entomologist and Professor of Tropical Public Health in the Department of Immunology and Infectious Disease at the Harvard School of Public Health (HSPH).
Ixodes ricinus, the castor bean tick, is a chiefly European species of hard-bodied tick. It may reach a length of 11 mm (0.43 in) when engorged with a blood meal, and can transmit both bacterial and viral pathogens such as the causative agents of Lyme disease and tick-borne encephalitis.
Amblyomma americanum, also known as the lone star tick, the northeastern water tick, or the turkey tick, is a type of tick indigenous to much of the eastern United States and Mexico, that bites painlessly and commonly goes unnoticed, remaining attached to its host for as long as seven days until it is fully engorged with blood. It is a member of the phylum Arthropoda, class Arachnida. The adult lone star tick is sexually dimorphic, named for a silvery-white, star-shaped spot or "lone star" present near the center of the posterior portion of the adult female shield (scutum); adult males conversely have varied white streaks or spots around the margins of their shields.
Human granulocytic anaplasmosis (HGA) is a tick-borne, infectious disease caused by Anaplasma phagocytophilum, an obligate intracellular bacterium that is typically transmitted to humans by ticks of the Ixodes ricinus species complex, including Ixodes scapularis and Ixodes pacificus in North America. These ticks also transmit Lyme disease and other tick-borne diseases.
Ixodes pacificus, the western black-legged tick, is a species of parasitic tick found on the western coast of North America. I. pacificus is a member of the family Ixodidae. It is the principal vector of Lyme disease in that region. I. pacificus larvae and nymphs typically feeds on lizards and small mammals, while adults typically feed on deer. It is an ectoparasite that attaches itself to the outside of its host and feeds on the host's blood. It can have a heteroxenous lifestyle or monoxenous life cycle depending on how many hosts it feeds on in each cycle. I. pacificus has a four stage life cycle that takes around 3 years to complete. These stages include egg, larva, nymph, and adult. They prefer dense woodland habitats or areas of brush and tall grass.
Ixodes hexagonus, also known by the common name hedgehog tick, is a tick species in the genus Ixodes. It is a parasite of the European hedgehog.
Borrelia miyamotoi is a bacterium of the spirochete phylum in the genus Borrelia. A zoonotic organism, B. miyamotoi can infect humans through the bite of several species of hard-shell Ixodes ticks, the same kind of ticks that spread B. burgdorferi, the causative bacterium of Lyme disease. Ixodes ticks are also the primary vector in the spread of babesiosis and anaplasmosis.
Borrelia mayonii is a Gram-negative, host-associated spirochete that is capable of causing Lyme disease. This organism can infect various vertebrate hosts such as humans via the bite of a black legged tick.
Ixodes angustus is a species of parasitic tick, whose range encompasses the majority of Canada and the United States, along with parts of northern Mexico. I. angustus is a member of the Ixodidae (hard-bodied) family of ticks. It is most abundant in cool, moist biomes such as riparian, boreal or montane zones. I. angustus is a host generalist and has been discovered feeding on more than 90 different host species, including humans and domestic dogs. I. angustus has been identified as a potential vector for Lyme disease but is not considered a principal vector due to the relative rarity with which it feeds on humans.