Dermacentor variabilis

Species of tick

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. It may take several days for the host to experience symptoms. Though D. variabilis may be exposed to Borrelia burgdorferi, the causative agent of Lyme disease, these ticks are not competent vectors for the transmission of this disease. The primary vectors for B. burgdorferi are the deer ticks 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. 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 life cycle 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 egg, a tick must obtain a blood meal at every stage to survive. Ticks can feed on mammals, birds, reptiles, and amphibians. Unlike most tick species, D. variabilis prefers the same host during all of its life stages.

Within North America, the normal range is in the eastern part of the continent, with some reports in California. At the northernmost extent of its geographical range, in Nova Scotia and Massachusetts, ticks are active from April to August, with a peak in May to June. In coastal Virginia, the adults are active from April to September or October, with peaks in May and July. In dogs additional symptoms may include lethargy, blood in the urine, irregular heartbeat, discolored spots on 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. 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. 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. The earlier the tick is removed from a host, the less likely it is to contract the illness.

The American dog tick 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. Doxycycline is given for 7–21 days dependent on the dosage. are recommended, along with other topicals, collars, and shampoos. Regularly checking dogs and oneself for ticks after hiking or playing in grassy areas and removing ticks as soon as possible decrease the chances a dog will contract a secondary illness carried by the tick. Tweezers are the most common removal method, but fine point tweezers are best to avoid tearing the tick and spreading possible infectious agents in the bite area. Spread the dog’s fur, grasp the tick as close to the skin as possible, and very gently pull straight upward in a slow, steady motion. Another removal method is a tick removal hook: one places the prongs of the device on either side of the tick and twists upward. Tick removal hooks are recommended in areas where ticks are common. Removing the tick with fingers is never a good idea because squeezing to grasp the tick could potentially inject more infectious material. Apply rubbing alcohol to the bite area afterward to thoroughly clean the wound.