Ixodes scapularis, black-legged tick, deer tick

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Taxonomic lineage

cellular organisms - Eukaryota - Fungi/Metazoa group - Metazoa - Eumetazoa - Bilateria - Coelomata - Protostomia - Panarthropoda - Arthropoda - Chelicerata - Arachnida - Acari - Parasitiformes - Ixodida - Ixodoidea - Ixodidae - Ixodinae - Ixodes - Ixodes scapularis

Brief facts

• Ixodes scapularis belongs to the family Ixodidae, or hard-bodied ticks, (as opposed to the Argasidae - soft-bodied ticks).
• Ticks may be classified as nest-dwelling (nidicolous) parasites or as field-dwelling (non-nidicolous) parasites. Ixodes scapularis is a non-nidicolous tick.
• The species is distributed in the eastern and northern Midwestern United States and southeastern Canada.
• Adult ticks are about 3 mm and dark brown to black in color. Adults exhibit sexual dimorphism.
• The tick is a vector for several bacterial, rickettsial, viral and protozoan diseases of animals and humans. Important tick-borne diseases include Lyme disease (Borrelia burgdorferi), tick-borne relapsing fever, babesiosis (Babesia microni), Rocky Mountain spotted fever, and many others. Apart of pathogen transmission, tick bites can cause paralysis, toxicoses, and severe allergic reaction.
• Various laboratories are currently focused on the genomic and proteomic analysis of ticks and in particular, tick salivary gland proteins (the sialome) as a source of targets for vaccine development. Tick research offers an opportunity to study parasite/host/pathogen relationships.

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Importance of feeding habits of the vector

• Changing hosts during its life cycle facilitates acquisition of pathogens that can be transmitted to the next host. In many instances, pathogens acquired by larval feedings are passed to the subsequent life stages (so-called, trans-stadial transmission). Ixodes scapularis is known to be able to feed on more than 100 hosts in North America (at least 52 species of mammals, 60 species of birds, and 8 species of reptiles).
• The relatively slow feeding process and the firm attachment to the host enhance dispersal of the ticks as the host moves about in the environment. For example, Ixodes scapularis can travel for miles while feeding on birds. Some ticks are carried between continents in this manner. The slow feeding is associated with the need to produce new cuticle to accommodate the ever increasing volume of blood.
• Tick's saliva, metabolites, and excesses of fluids are secreted back to the host. During this process pathogens are transmitted to the host. Upon completion of feeding, the female can weigh 100 to 120 times its original weight, but because so much water is secreted back to the host, the total volume of blood ingested may be two to three times the amount calculated from post-feeding weight.

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Feeding stages

1. Appetence (hunger) - waiting for or actively seeking a host. Ixodes scapularis congregate along animal trails, rest on vegetation and wait for appropriate hosts to brush past them.
2. Engagement - adherence to the host's fur, feathers, or skin.
3. Exploration - searching the host's external surface for a suitable attachment site.
4. Penetration - insertion of the mouthparts into the host's skin, "tasting the host".
5. Attachment - feeding site is established
6. Ingestion - start of active feeding. There is little if any increase in the parasite's weight during first 24 hours of feeding.
7. Engorgement (satiation) - partial or complete blood meals taken. Tick's weight increases gradually and slowly over several days, followed by a rapid increase on the last day. It is believed that high dosages of Borrelia burgdorferi (Lyme disease) are transferred during the later period of feeding.
8. Detachment - withdrawal of mouthparts.
9. Disengagement - tick drops off of the host to complete its current life stage using obtained nutrients.

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Life cycle

I. scapularis is a three-host tick; the larva, nymph and adult stages each feed on separate hosts. Although the life cycle of the tick species is relatively long in the wild (2 years), one generation can be produced in the lab within 9 to 12 months.

• egg beginning in May, engorged adult females typically lay between 1000 to 3000 eggs on the forest floor at the site where they detached from their hosts
• larval eggs hatch into tiny six-legged larvae; peak of larval activity occurs in August; larvae attach and feed on a wide variety of mammals and birds, primarily on white-footed mice after feeding for three to five days, engorged larvae drop from the host to the ground where they overwinter
• molting in May, larvae molt into nymphs
• nymph nymphs feed on a variety of hosts for three to four days; engorged nymphs detach and drop to the forest floor where they molt into the adult stage, which becomes active in October; human exposure to blacklegged ticks is greatest during the summer months when high nymphal and human outdoor activity coincide
• adult adult ticks remain active through the winter on days when the ground and ambient temperatures are above freezing; adult female ticks feed for five to seven days while the male tick feeds only sparingly, if at all; adult ticks feed on large mammals, primarily upon white-tailed deer

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Brief notes on reproduction in Ixodes ticks

• Unlike all other ixodid genera (metastriate ticks) in which copulation occurs only during feeding, Ixodes ticks (prostriate ticks) can copulate before (preprandial mating) or during the blood meal. This is possible because Ixodes females are able to store sperm until engorgment after which they can complete their reproductive function and lay eggs. This mating strategy can extend the mating season to nine months or more.
• The mouthparts of male Ixodes ticks are more specialized for mating than those of other ticks; their structure seems poorly suited for host attachement and feeding. Usually Ixodes ticks' mating proceeds in the following behavioral sequence: the male touches female genital with his mouthparts, then, he inserts the mouthparts in her genital pore; the sac-like spermatophore then protrudes from his genital opening; he withdraws his mouthparts and grasps the inflated spermatophore with his chelicrae; the chelicerae are then used to tuck the margin of the spematophore into the female's genital pore; finally, the spermatophore everts itself into female's genital tract and deflates. Although mating pairs may remain in sexual contact for days, spermatophore generally passes from male to female in less than a minute.
• Some Ixodes ticks employ a form of sexual parasitism in which males gain nourishment from females during prolonged sexual contact. For example, male I. holocyclus actually imbibe hemolymph from a feeding female.

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Tissue

• tick
  • capitulum or gnathosoma
    • mouthparts
      • palps 2 four-segmented palps, each of which has numerous chemosensory organs; the palps are pressed against the skin during the feeding
      • chelicerae two sclerotized, 2-segmented tubular chelicerae extends from the basis capituli and are located medially to the palps
      • digits movable sharp digits are located laterally and are used to cut the skin
      • hypostome the organ is used as food canal and as holdfast organ; the size and shape of the hypostome and the arrangement of denticles (teeth) on its surface are important for species identification
  • body or idiosoma
    • legs 6 (nymph) or 8 legs (adult) are attached to the body
• • central
    nervous
    system MeSH in ticks called synganglia

Major Ixodes-born diseases in United States

Disease	Causative organism	Organism description	Disease description	Region
Lyme disease	Borrelia burgdorferi	Bacteria (spirochete); invade blood and tissues; white-footed mouse is believed to be a natural reservoir	Erythematous lesion at site of bite; fibromyalgia, malaise, fatigue, arthritis, neurologic manifestations (abnormalities in mood, memory, and sleep )	Connecticut, Midwest
Babesiosis	Babesia microti	Protozoa	Malaria-like blood parasitic disease; can be asymptomatic (especially in people with healthy spleen); mild to severe fevers and anemia	New York, Massachusetts, Minnesota
Anaplasmosis	Anaplasma phagocytophilum (Ehrlichia phagocytophilum)	Obligate intracellular gram-negative bacteria, rickettsia, infects neutrophils	Fever, severe headache, muscle aches (myalgia), chills and shaking, similar to the symptoms of influenza, can be fatal	California, Colorado, Connecticut, Florida, New Jersey, New York, Maryland, Minnesota, Wisconsin
Rickettsiosis (Rocky Mountain spotted fever (RMSF), also tick typhus)	Rickettsia parkeri	Obligate intracellular gram-negative bacteria, rickettsia, grow within damaged cells lining blood vessels	The onset of symptoms is abrupt with headache, high fever, chills, muscle pain, and then a rash; blood vessel inflammation (vasculitis) is common	Florida, Georgia, Kentucky, Mississippi, Oklahoma, and South Carolina

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Ixodes scapularis life cycle diagram

 

 
Photo credit: Dobson A et al. PLoS Med. 2006 Jun;3(6):e231.(PMID: 16729846)

Two Juvenile White-Footed Mice (Peromyscus leucopus) That Have Been Placed in a Plastic Pail before Being Marked with Ear Tags and Released.

Mice are important reservoirs for the pathogens that cause Lyme disease, human babesiosis, human granulocytic anaplasmosis, hantavirus pulmonary syndrome, and many other diseases. They thrive in low-diversity vertebrate communities that support few predators and competitors.

 

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Photo credit: Schwan TG and Piesman J Emerg Infect Dis. 2002 February; 8(2): 115–121.

Dorsal view of a female Ixodes scapularis (family Ixodidae, hard ticks), a vector of Borrelia burgdorferi (left), and a female Ornithodoros hermsi (family Argasidae, soft ticks), the vector of B. hermsii (right).

 

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Article: Sumner JW et al. Emerg Infect Dis. 2007 May; 13(5): 751–753.

Adult Amblyomma maculatum (the Gulf Coast tick), a vector of Rickettsia parkeri. A) Female; B) Male. Photographs courtesy of James Gathany, Centers for Disease Control and Prevention.

 

References

• Anderson JF, Magnarelli LA. Biology of ticks. Infect Dis Clin North Am. 2008
• Swanson SJ, Neitzel D, Reed KD, Belongia EA. Coinfections acquired from ixodes ticks. Clin Microbiol Rev. 2006 Oct
• Spach DH et al. Tick-borne diseases in the United States. N Engl J Med. 1993 Sep 23
• Kiszewski AE et al. Mating strategies and spermiogenesis in ixodid ticks. Annu Rev Entomol. 2001;46:167-82.
• Kaufman RW. Gluttony and sex in female ixodid ticks: how do they compare to other blood-sucking arthropods? J Insect Physiol. 2007 Mar;53(3):264-73.
• Major topic "ticks": free full text articles in PubMed

Websites

• Wikipedia: Ixodes scapularis
• VectorBase: I. scapularis

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