Canis ISSN: 2398-2942

Dermacentor andersoni

Synonym(s): Rocky Mountain wood tick

Contributor(s): Maggie Fisher, Susan E Shaw, Ian Wright




  • Class: Arachnida; subclass: Acari
  • Order: Metastigmata or Ixodida
  • Family: Ixodidae
  • Genus: Dermacentor
  • Species: D. andersoni

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Clinical Effects



  • Preferred hosts for the adults are large herbivores but dogs and people may be infested.
  • Nymphs and larvae usually parasitize small rodents.
  • Preferred habitats include grassland or shrubland with moist conditions and shrub cover.
  • Preferred environment is one of high humidity with mild winters.


  • Three host tick 3-host tick, ie each stage falls off the host into the environment after feeding, molts and finds another host for the next stage.
  • Life cycle may take 1 year, or 2 years with stages overwintering.

Pathological effects

  • Pruritus in susceptible dogs, local hypersensitivity with tick-bite site ulceration and secondary pyoderma Skin: deep pyoderma.
  • Tick paralysis if present in sufficient numbers, primarily a problem in calves.
  • Vector ofRickettsia rickettsi (Rocky Mountain spotted fever) in dogs and humans.
  • Vector of tularemia (Francisella tularensis), a human bacterial infection.
  • Adults can engorge with 0.5-2 ml of blood so potential for anemia if present in large numbers.
  • Potential vector for Colarado tick fever virus.


Control via chemotherapies

  • Amitraz Amitraz , Fipronil Fipronil , pyrethroids, pyriprole and isoxazolines are approved for treatment and prophylaxis in dogs.

Control via environment

Largely impractical except where infestation is confined to a limited space such as kennels.

  • Outdoor premises control of ticks includes use of carbamates and synthetic pyrethroids. Older insecticides have efficacy but their use is controlled by regulatory approval.
  • Synthetic pyrethroids for indoor control (and for use in cars, kennels and cages). Older drugs under regulatory control but may be used by commercial pest exterminators.
  • Management of garden habitat, keeping grass short and shrubbery to a minimum.


  • None available for tick control. See control of tick-borne diseases Tick control.

Other countermeasures

  • Checking for ticks every 24 hours and removal with a tick hook using a 'twist and pull' action.
  • Important to remove tick as soon as it is found to reduce risk of disease transmission.
  • If the tick is removed but the mouthparts remain this will increase the risk of local soft tissue reaction and disease transmission.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Niebylski M L, Peacock M G & Schwan T G (1999) Lethal effect of Rickettsia rickettsi on its tick vector (Dermacentor andersoni). Applied Environmental Microbiology 65 (2), 773-778 PubMed.

Other sources of information

  • Wall R & Shearer D S (Editors) (2008) Veterinary Ectoparasites: Biology, Pathology and Control, 2nd edn, Blackwell Science Ltd, London, pp 71-74.
  • Baker A S (1990) Mite and ticks of domestic animals: An identification and information source. The Natural History Museum, The Stationery Office, London, pp 176-179.