Ticks are a common external (on the skin) parasite of many animals, including dogs. Ticks are not insects like fleas, flies, and lice, but are arachnids like mites and spiders. There are approximately 850 species of ticks worldwide. Scientists have classified ticks into two families based upon their structure: Ixodidae and Argasidae.
Ixodid Ticks
The tick family Ixodidae consists of ticks that have a hard outer covering called a scutum, and therefore, are termed hard-shelled ticks. Table 1 lists the most important hard-shelled ticks for dogs and cats.
Table 1: Ticks commonly found on dogs and cats
| Tick | Common Name | Geographic Distribution in U.S. | Tick-associated Disease(s) in Dogs and Cats* |
|---|---|---|---|
| Amblyomma americanum | Lone star tick | Southeast, Midsouth and coastal Northeast | Ehrlichiosis, tularemia, Rocky Mountain spotted fever, tick paralysis |
| Anblyomma maculatum | Gulf Coast tick | Gulf Coast to Midsouth and lower Midwest | Hepatozoonosis |
| Dermacentor variabilis | American dog tick | Eastern 2/3 of U.S.; West Coast | Ehrlichiosis, tularemia, Rocky Mountain spotted fever, cytauxzoonosis, tick paralysis |
| Dermacentor andersoni | Rocky Mountain wood tick | Northwest; Northern Rocky Mountain states | Rocky Mountain spotted fever, tularemia, cytauxzoonosis, tick paralysis |
| Ixodes scapularis | Eastern black-legged tick (deer tick) | States east of and adjacent to Mississippi River; Eastern TX and OK | Lyme disease, anaplasmosis, tick paralysis |
| Ixodes pacificus | Western black-legged tick | West Coast and Eastern NV | Lyme disease, anaplasmosis |
| Rhipicephalus sanguineus | Brown dog tick | Throughout U.S | Ehrlichiosis, Rocky Mountain spotted fever, babesiosis, anaplasmosis, hepatozoonosis, haemobartonellosis |
The geographic distribution of ticks in the United States may be increasing, as certain species are being found in areas they have not been identified in previously. This means that the tick-borne diseases caused by these ticks are also spreading across the United States. See links to articles on these diseases at the bottom of this article.
Argasid Ticks
The family Argasidae contains the argasid ticks, which are soft-shelled. Their body lacks a scutum. An argasid has its head located ventrally (on the underside of its body) and when the tick is viewed from above, the head cannot be seen. The soft-shelled ticks or Argasids are fewer in number. The most well known soft- shelled tick is Otobius megnini, also known as the Spinose Ear Tick. It is most common in the Southwest and usually attaches to the ears of animals.
Tick Anatomy
All ticks have three pairs of legs during the immature stage and four pairs as an adult. They crawl but cannot fly since they have no wings. Ticks possess a sensory apparatus called Haller's organ. This structure senses odor, heat, and humidity. This is how the ticks locate their food source. They climb upon tall grass (called questing) and when they sense an animal is close by, they crawl on.
A Tick's Diet
A tick's diet consists of only blood. The tick embeds its mouthparts into the animal's (or human's) skin and sucks the blood. Except for the eggs, ticks require a blood meal to progress to each successive stage in their life cycle.
The Tick Life Cycle
Most ticks are what we call three host ticks, that is, during their development which takes two years, they feed on three different hosts. All ticks have four stages to their life cycle: egg, larvae (seed tick), nymph, and adult. Let us look at the life cycle of the deer tick, as an example.
Adult female deer ticks lay eggs on the ground in spring. Later in the summer (depending on moisture and temperature), the eggs hatch into larvae. The larvae, which are the size of the period at the end of this sentence, find their first host, which is usually a bird or rodent, live off its blood for several days, then detach and fall back onto the ground. For deer ticks, this most commonly occurs in the month of August. On the ground, the well-fed larvae now molt into the next stage and are called nymphs.
Other species of ticks may be at peak activity for each life stage at different times of the year than the deer tick. Your local university or health department may have information on peak tick activity in your area.
Tick-Borne Diseases
Ticks can transmit or cause many different diseases in both pets and people. Anaplasmosis is a tick-borne disease that can cause fever, vomiting, diarrhea, bleeding, and occasionally neurological signs.
Babesiosis (Piroplasmosis) is an organism that infects the red blood cells of dogs and sometimes people. The red blood cells are destroyed, resulting in anemia.
Cytauxzoonosis is a tick-borne disease of cats that has a high mortality rate. Prevention is key, as an effective treatment is still being investigated.
Ehrlichiosis is another tick-borne disease that infects the white blood cells.
Haemobartonellosis in Dogs and Cats is a disease that targets red blood cells and is transmitted by both fleas and ticks.
Hepatozoonosis is a protozoal infection transmitted by ticks that can be fatal if not treated. Lyme Disease is a well known tick-borne disease that causes lameness and joint swelling.
Rocky Mountain Spotted Fever affects only dogs and humans with clinical disease, which can range in severity from no signs to multi-organ failure.
Tick Paralysis causes a reversible paralysis that resolves once the tick is removed.
Tularemia in Dogs and Cats causes ulcers, fever, and weight loss. Humans can be infected with tularemia.
See our article on Tick Control for more information on how to prevent tick-borne diseases in dogs.
Article by: Race Foster, DVM and Angela Walter, DVM