Internal and external parasites are a constant nuisance and threat to your pets, and in many cases, to you and your family as well. Most parasites are relatively easily picked up and transferred between animals, and many are Zoonotic (meaning they can infect humans as well); thankfully, most are also relatively easy to prevent and protect against. The following is a general overview of some of the most commonly seen pests.


Ectoparasites are parasites that live on the outside of the host (your pet). The most common of these include fleas, ticks, and lice. “But we don’t have fleas here in Arizona,” right? FALSE! Fleas and ticks are commonly seen here in Prescott and most other areas of the state. In fact, the Four Corners and Flagstaff areas routinely see fleas that carry the bacteria Yersinia Pestis, which causes the Plague, a disease that can be devastating in humans if not treated promptly. Fleas also routinely carry tapeworm eggs, and when ingested infest the pets intestines – but more on GI parasites later.

Ticks are also more prevalent in this area than people often believe. They thrive on the wildlife and in vegetated areas, and easily find hosts through a process called “questing,” during which they wait at the tips of grasses and leaves until a mammal brushes by, then they quickly climb aboard. Ticks may carry numerous diseases, and though historically Arizona has a low prevalence of many of these diseases (I.E. Lyme disease) case numbers of illnesses such as Rocky Mountain Spotted Fever have been on the rise in recent years according to the Centers for Disease Control and the Arizona Department of Health.

Internal Parasites

These are numerous and come in many shapes and sizes. From protozoal single celled organisms to large worms, many of these parasites are contracted through direct contact – meaning consumption of an infected animal, or fecal-oral transmission via ingestion of fecal matter, as most parasite eggs are shed in the feces.

Gastrointestinal worms include roundworms, tapeworms, hookworms, whipworms; those first three are relatively easily transmitted from an infested pet to you. The following table (courtesy of Merck Manual) discusses transmission and possible clinical signs that may be present when people are infected:

Heartworms are different in that they take up residence in the blood vessels around the heart and lungs. These parasites are deadly for pets, as they interfere with blood flow and lead to changes in the heart over time. Heartworms are transmitted by mosquitoes, and while we do not have a high prevalence of the disease in Yavapai County, we do still see cases and we recommend that dogs remain on preventative medication year-round.

Testing and Prevention

We recommend patients have an exam twice yearly. During these exams your pets are checked for external parasites. A fecal should also be performed to check for parasite eggs, and a deworming protocol will be determined based on the specific results.

A blood parasite test should be performed prior to starting monthly heartworm preventative, and every other year thereafter as long as the patient is on consistent preventative. If a patient is unable to take the monthly medication due to health or other concerns, the blood parasite test should be performed every 6 months to monitor for evidence of infection. This test specifically checks for heartworms, as well as the more prevalent tick borne diseases.

Healthy animals have as few parasites as possible; there are numerous flea and tick preventatives as well as heartworm and gastrointestinal worm preventatives available to keep patients healthy. The best parasite prevention and treatment protocol is one made with your veterinarian, together we will make decisions to keep your pet healthy and happy, and without unwanted guests.

Ashley Joy, DVM
Prescott Animal Hospital