Ixodes scapularis, black-legged tick, deer tick

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.


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.

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.