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Dermacentor variabilis

Dermacentor variabilis
Dermacentor variabilis, U, Back, MD, Beltsville 2013-07-08-19.15.11 ZS PMax.jpg
Dermacentor Variabilis Male.jpg
Scientific classification
D. variabilis
Binomial name
Dermacentor variabilis
(Say, 1821)
Dermacentor variabilis range map.svg
Normal range in red; other reports in blue

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 (Francisella tularensis). It is one of the best-known hard ticks. Diseases are spread when it sucks blood from the host, which could take several days for the host to experience some symptoms.

Though D. variabilis may be exposed to Borrelia burgdorferi, the causative agent of Lyme disease,[1] these ticks are not competent vectors for the transmission of this disease.[2][3][4] The primary vectors for B. burgdorferi are the deer tick Ixodes scapularis in eastern parts of the United States, Ixodes pacificus in California and Oregon, and Ixodes ricinus in Europe. D. variabilis may also carry Anaplasma phagocytophilum, the causative agent of human granulocytic anaplasmosis, and Ehrlichia chaffeensis, the causative agent of human monocytic ehrlichiosis.[1]

Dermacentor ticks may also induce tick paralysis by elaboration of a neurotoxin that induces rapidly progressive flaccid quadriparesis similar to Guillain–Barré syndrome. The neurotoxin prevents presynaptic release of acetylcholine from neuromuscular junctions.


The lifecycle of ticks can vary depending on the species. Most ticks go through four stages: egg, six-legged larva, eight-legged nymph, and adult. After hatching from the eggs, ticks must eat blood at every stage to survive. Ticks can feed on mammals, birds, reptiles, and amphibians. Most ticks prefer to have a different host animal at each stage of their lives. Although some tick species, such as D. variabilis, prefer to feed on the same host during all life stages.[5]

Dermacentor species lifecycle

Distribution and seasonal activity

Within the United States, the normal range is in the eastern part of the country, with some reports in California. The northernmost geographical range of Nova Scotia and Massachusetts seasonal activity is from April to August with a peak in May to June.[6] In coastal Virginia, the adults are active from April to September or October, with peaks in May and July.[6] Seasonal activity in Ohio is from late April to September, with peaks in May to June and another smaller peak in August to September.[6] In Georgia, adults are active from late March to August, with peaks in early May, late May, and late June.[6] Florida adult activity is from April to July, with activity being restricted by high summer temperatures and low winter humidity. [6]

D. variabilis tick

Disease transmission

Ticks that are feeding cause the transmission of pathogens to the host. Depending on the tick species and its stage of life, preparing to feed can take from 10 minutes to 2 hours.[5] When the tick finds a feeding spot, it grasps the skin and cuts into the surface, where it then inserts its feeding tube.[5] Many species also secrete a cement-like substance that keeps them firmly attached during the meal.[5] The feeding tube can have barbs to help keep the tick in place.[5] Ticks also can secrete small amounts of saliva with anesthetic properties so that the animal or person cannot feel that the tick has attached itself.[5] Therefore, unless one feels the tick crawling, noticing the tick is difficult. If the tick is in a sheltered spot, it can go unnoticed, so can slowly suck the blood for several days. If the host animal has a blood-borne infection, the tick will ingest the pathogens with the blood.[5] Small amounts of saliva from the tick may also enter the skin of the host animal during the feeding process.[5] If the tick contains a pathogen, the organism may be transmitted to the host animal in this way.[5] After feeding, most ticks drop off and prepare for the next life stage.[5] At its next feeding, it can then transmit an acquired disease to the new host.[5]

Symptoms of Rocky Mountain Spotted Fever can first be noted by the appearance of a rash around the wrists and ankles that moves slowly up to the rest of the body and develops within 2–5 days. Other symptoms include depression, lethargy, anorexia, blood in the urine, irregular heartbeat, discolored spots along the skin (often bruised or purplish in color), inability to walk normally, loss of coordination, swelling or edema in the limbs, sudden bleeding from the nose or in the stools, difficulty with blood clotting, swollen lymph nodes, pain in the eyes, inflammation, hemorrhage, or conjunctivitis in the mucosal membranes.[7]

Symptoms of tularemia usually appear within 3–5 days, but can appear as late as 21 days after transmission. Oftentimes, patients experience chills, swollen lymph nodes, and an ulceration at the site of the bite.[8]

A tick bite does not automatically transfer diseases to the host. Instead, the tick must be attached to the host for a period of time, generally 6–8 hours, before it is capable of transferring disease.[8] Disease transmission can occur as quickly as 3-6 hours after a bite occurs.[9] Therefore, the earlier the tick is removed from a host, the less likely it is to contract the illness.

Treatments and prevention in dogs

The American dog tick is a rather colorful tick and is commonly found in highly wooded, shrubby, and long-grass areas. Tick numbers can be reduced by cutting the grass, which creates a low-humidity environment, which is undesirable to ticks. Pesticides can also be used and are most effective when applied to vegetation that has been cut to a short level.[8] Doxycycline is the medication of choice to treat Rocky Mountain spotted fever in dogs.[10] Doxycycline is given 7-21 days dependent on the dosage.[10] Tetracycline is effective and administered more frequently, being given for 14-21 days.[10] Other antibiotic choices would include enrofloxacin and chloramphenicol.[10] Veterinary-approved flea and tick preparations, such as Nexguard and Frontline, are recommended, along with other topicals, collars, and shampoos.[11] Regularly checking dogs and oneself for ticks after hiking or playing in grassy areas, and[11] removing ticks as soon as possible decrease the chances a dog will contract a secondary illness carried by the tick.[11] The use of tweezers is the most common removal method, but fine-point tweezers are the best to avoid tearing the tick and spreading possible infections in the bite area.[9] Spread the dog’s fur and grasp the tick closest to the skin and very gently pull straight upward in a slow, steady motion.[9] Another removal method is the use of a tick removal hook such as the Tick Twister or the Tick Stick, where one places the prongs on either side of the tick and twists upward.[9] Tick removal hooks might be the most useful in areas where ticks are a normal occurrence.[9] Removing the tick with fingers is never a good idea because the squeezing to grasp the tick could potentially inject more infectious material into the pet.[9] Applying rubbing alcohol to the bite area to thoroughly clean the wound is recommended.[9]

See also


  1. ^ a b Kevin Holden; John T. Boothby; Sulekha Anand & Robert F. Massung (2003). "Detection of Borrelia burgdorferi, Ehrlichia chaffeensis, and Anaplasma phagocytophilum in Ticks (Acari: Ixodidae) from a Coastal Region of California". J. Med. Entomol. 40 (4): 534–9. doi:10.1603/0022-2585-40.4.534. PMID 14680123.
  2. ^ Joseph Piesman & Christine M. Happ (1997). "Ability of the Lyme disease spirochete Borrelia burgdorferi to infect rodents and three species of human-biting ticks (blacklegged tick, American dog tick, lone star tick) (Acari:Ixodidae)". J. Med. Entomol. 34 (4): 451–6. doi:10.1093/jmedent/34.4.451. PMID 9220680.
  3. ^ F. H. Sanders & J. H. Oliver (1995). "Evaluation of Ixodes scapularis, Amblyomma americanum, and Dermacentor variabilis (Acari: Ixodidae) from Georgia as vectors of a Florida strain of the Lyme disease spirochete, Borrelia burgdorferi". J. Med. Entomol. 32 (4): 402–426. doi:10.1093/jmedent/32.4.402. PMID 7650697.
  4. ^ Stanley W. Mukolwe; A. Alan Kocan; Robert W. Barker; Katherine M. Kocan & George L. Murphy (1992). "Attempted transmission of Borrelia burgdorferi (Spirochaetales: Spirochaetaceae) (JDI strain) by Ixodes scapularis (Acari: Ixodidae), Dermacentor variabilis, and Amblyomma americanum". J. Med. Entomol. 29 (4): 673–7. doi:10.1093/jmedent/29.4.673. PMID 1495078.
  5. ^ a b c d e f g h i j k "How ticks spread disease | Ticks | CDC". 2019-04-09. Retrieved 2019-04-24.
  6. ^ a b c d e Burg, J. G. (2001). "Seasonal activity and spatial distribution of host-seeking adults of the tick Dermacentor variabilis". Medical and Veterinary Entomology. 15 (4): 413–421. doi:10.1046/j.0269-283x.2001.00329.x. ISSN 1365-2915.
  7. ^ "Rocky Mountain Spotted Fever in Dogs | petMD". Retrieved 2019-04-24.
  8. ^ a b c "American dog tick - Dermacentor variabilis (Say)". Retrieved 2016-05-05.
  9. ^ a b c d e f g "How to Remove a Tick from Your Dog". American Kennel Club. Retrieved 2019-04-24.
  10. ^ a b c d "Rocky Mountain Spotted Fever in Dogs". vca_corporate. Retrieved 2019-04-24.
  11. ^ a b c "Flea and Tick Prevention Tips: Keep Your Dogs Safe This Spring". American Kennel Club. Retrieved 2019-04-24.

External links