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Pet Parasites in the West: A Regional Overview of Species and Risks

by Elizabeth Claire Alberts
Reviewed by Sarah J. Wooten, DVM on 02/23/2024. Published on 02/23/2024
Great Dane dog enjoying a Pacific Northwest park
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The western states of the U.S. are known for their wide-open spaces, stunning wilderness areas, and diverse wildlife. For dogs, cats, and pet parents who enjoy the outdoors, this region of the country can be a great place to visit or live. But pets who spend a lot of time outside in the western U.S. run the risk of being infested by parasites like ticks, fleas, and the mosquitoes that transmit heartworm disease. Even indoor pets are at risk. 

To keep your pet safe, it’s important to educate yourself about how parasite risks differ between geographical regions and states and know how to protect your dog or cat.

Keep reading for a regional guide to heartworm disease, fleas, and ticks in the Western states of Alaska, Arizona, California, Colorado, Hawaii, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington, and Wyoming.

Heartworm Disease in the West

A Border Collie on a trail in the Redwood forest in Northern California

Heartworms are an internal parasite that is spread to dogs and cats by mosquitoes. While both dogs and cats can get heartworms, dogs are the preferred host of heartworms. “Heartworms are transmitted through mosquito bites,” explains Los Angeles-based veterinarian Dr. Sehaj Grewal, the CEO of TheMelroseVet.com. “It takes about six months for the worms to mature and (start causing symptoms in pets.”

Heartworms not only affect the heart, they can also impact a pet’s lungs and blood vessels. Once these parasites are inside your pet, they can cause severe lung disease, heart failure, and damage to other organs if untreated, according to the American Heartworm Society. 

When compared to other parts of the U.S., such as the Atlantic and Gulf coasts, the incidence of heartworm disease in the West is generally lower. But that doesn’t mean it’s non-existent. Southwest states with warmer climates typically have more cases compared to states in the Pacific Northwest that experience frigid cold snaps over the winter. In Alaska, the only documented heartworm cases are in pets with a history of travel outside the state. However, as global temperatures rise in response to climate change and people travel more with their pets, cases of heartworm disease are popping up in new places.

In addition, heartworm disease is becoming more frequent in some states due to dog and cat relocation programs led by animal welfare organizations and pet adoption agencies, says Dr. Cassan Pulaski, a clinical assistant professor and director of the Parasitology Diagnostic Laboratory at the University of Georgia’s College of Veterinary Medicine. One of the effects of that is when these animals are relocated, if they are infested, they bring parasites with them, Dr. Pulaski says.

For example, increased animal relocation could be a contributing factor to a recent rise in heartworm cases in Colorado. According to a 2019 study published in Parasites & Vectors, animal shelters and rescue groups imported more than 114,000 dogs into Colorado between 2014 and 2017. Many of these imported dogs originated from states with high prevalence of heartworm disease, such as New Mexico, Texas, and Oklahoma. Around the same time, the state saw a 67.5 percent increase in heartworm disease in dogs in Colorado, between 2013 and 2017. 

Regardless of where you live in the West, the American Heartworm Society recommends year-round heartworm prevention — even regions with cold winters. 

Fleas in the West

A closeup of a flea in a pet's fur

Fleas are found in just about every U.S. state, making it hard to escape these pesky, blood-feeding insects. Yet, there are certain areas — and times — where fleas are more abundant, Dr. Pulaski says.

“When we think about the states that are the most problematic, they’re going to be states that are hot, warm, and very moist,” Dr. Pulaski says. “Fleas don’t particularly like cold, and they don’t like dry.”

So when temperatures rise, the risk of your pet getting fleas goes up, even in states where fleas aren’t as common. That being said, fleas can be a problem year-round (or nearly year-round) for many Western states. (Compared to other U.S. states, Alaska and Wyoming have shorter flea seasons.)

“Fleas are going to be emerging and going to be really happy at about 70 or 75 degrees [Fahrenheit],” Dr. Pulaski adds “but they can go into a dormant state at around 50 or so degrees and stay in that dormant state for a long time.” 

The most common flea to affect pets is the cat flea (Ctenocephalides felis), which, despite its name, affects both dogs and cats. Besides making your dog or cat itchy, cat fleas can lead to health conditions like anemia or flea allergy dermatitis and potentially transmit other parasites like tapeworms.

Dogs and cats can also carry various types of rodent fleas that are known to transmit the bubonic plague, according to the New Mexico Department of Health. Since 1970, more than half of plague cases in the U.S. have been reported in New Mexico. In 2017, fleas were found to be carrying the bacteria for the bubonic plague in two counties in northern Arizona. In 2023, Wyoming also recorded its first known case of bubonic plague in a pet cat, and a recent case of human plague in Oregon was likely caused by a pet cat.

Pets can get fleas from “infested animals or environments,” Dr. Grewal says. Spending time outside in “grassy or wooded areas increases the risk” of your pet getting fleas, he adds. Dr. Grewal recommends regular flea control and keeping your indoor and outdoor spaces clean.

Ticks in the West

A cat on a leash at the Grand Canyon

While there are many different ticks found in the western states of the U.S., three of the most common ones are the American dog tick (Dermacentor variabilis), the western blacklegged tick (Ixodes pacificus), and the brown dog tick (Rhipicephalus sanguineus). However, the prevalence of ticks varies for each state. In Alaska, for instance, ticks are not very common, but coastal states like California and Oregon tend to have relatively high tick activity.

If your dog or cat gets a tick, it doesn’t necessarily mean they will get a tick-borne disease. But left unnoticed and untreated, pets with ticks can be at risk of a range of issues, including serious illnesses like Lyme disease and Rocky Mountain spotted fever. 

“Pet owners should be aware of the specific tick species in their area and use preventive measures to protect against tick-borne diseases,” says Dr. Jessica Jensen, an Oregon-based veterinarian with the mobile pet care service, The Vets. “Regular grooming and tick checks are essential for effective tick control. Consultation with a veterinarian can provide personalized guidance based on local tick species and associated risks.”

Both you and your pet are most likely to encounter ticks while walking through wooded or bushy areas, or places with long grass. You can protect yourself by wearing repellent, shirts with long sleeves, and pants. As for your pet, talk to your veterinarian about regular tick and flea control. 

Below are common tick-borne diseases impacting pets in the West and the tick species that can cause them: 

  • Anaplasmosis: Western blacklegged tick (Ixodes pacificus)
  • Colorado tick fever: Rocky Mountain wood tick (Dermacentor andersoni)
  • Ehrlichiosis: Brown dog tick (Rhipicephalus sanguineus)
  • Lyme disease: Western blacklegged tick
  • Rocky Mountain spotted fever: Rocky Mountain wood tick, brown dog tick, American dog tick (Dermacentor variabilis), Pacific Coast tick (Dermacentor occidentalis)
  • Tick-borne relapsing fever: Soft ticks in the genus Ornithodoros
  • Tick paralysis: Rocky Mountain wood tick, American dog tick
  • Tularemia: American dog tick, lone star tick (Amblyomma americanum), Rocky Mountain wood tick

Ticks in Alaska

No matter the season, Alaska has a ton of outdoor activities you can enjoy with your furry friend. Together, you can explore state parks, relax at campgrounds, or go kayaking. While parasites are less of a concern in this cold Pacific Northwest state, there has been an increasing number of flea and tick cases there, due to the world’s changing climate and people transporting  infected pets into the state from other places. 

According to the state of Alaska’s Department of Fish and Wildlife, American dog ticks and brown dog ticks have occasionally been found on companion animals. If you do find a tick on your pet, the state recommends that you carefully remove it, put it into a container, and send it to the Alaska Submit-a-Tick program for testing and data collection. 

Types of Ticks in Alaska Dangerous for Pets

  • American dog tick
  • Brown dog tick 
  • Lone star tick (rare)
  • Rocky Mountain wood tick (rare)
  • Squirrel tick

Tick-Borne Diseases Found in Alaska

While ticks found in Alaska have the ability to carry and spread the bacteria that causes Rocky Mountain spotted fever, ehrlichiosis, tularemia, and other tick-borne diseases, so far researchers have not found any evidence that ticks currently in the state are carrying the germs that cause these diseases.

Ticks in Arizona

While most national parks in the U.S. do not permit pets, Arizona is an exception to the rule. You’re allowed to take your dog around the Rim Trail of the Grand Canyon and through many parts of the Petrified Forest National Park. But if your dog or cat is out adventuring in Arizona, you will need to be mindful of ticks, which can affect your pet year round.

In Arizona, ticks are moving into new locations and tick-borne diseases are spreading across the state, according to the University of Arizona. The most common tick found in Arizona is the brown dog tick, which can transmit several diseases to dogs and cats. Western blacklegged ticks and Rocky Mountain wood ticks are also found in Arizona, but they’re only found in a limited part of the state’s north, according to data collected by the Centers for Disease Control and Prevention (CDC). 

Types of Ticks in Arizona Dangerous for Pets

  • Brown dog tick
  • Rocky Mountain ticks
  • Western blacklegged ticks

Tick-Borne Diseases Found in Arizona

  • Anaplasmosis
  • Ehrlichiosis
  • Lyme disease
  • Rocky Mountain spotted fever

Ticks in California

California has it all — sandy beaches, snow-capped mountains, and wide stretches of desert. Adventure-loving dogs and cats have no shortage of activities to do in this coastal state. But California’s diverse climate means that ticks can affect your pet at any time of the year. Not only that, but longer periods of rain that are now occurring in the state have expanded the range of disease-carrying ticks and are keeping them out for longer periods. For instance, California has seen an uptick in Rocky Mountain spotted fever, a potentially fatal tick-borne disease that can affect both people and pets.

Types of Ticks in California Dangerous for Pets

  • American dog tick
  • Brown dog tick
  • Pacific Coast tick
  • Western blacklegged tick

Tick-Borne Diseases Found in California 

  • Anaplasmosis
  • Ehrlichiosis
  • Lyme disease
  • Rocky Mountain spotted fever
  • Tularemia

Ticks in Colorado

With its mountains, canyons, and waterways, Colorado has plenty of outdoor attractions for you to explore with your pet. However, you should be aware that ticks and the diseases they carry are becoming more prevalent in Colorado. 

According to CDC data, there are two ticks that mainly affect pets in the state: the brown dog tick and the Rocky mountain wood tick. However, a 2022 study published in the journal Ticks and Tick-borne Diseases found that ticks like the American dog tick are also present in Colorado. The lone star tick has also been making an occasional appearance, likely after being carried by animals from other states, according to the Colorado Tick-borne Disease Awareness Association.

Types of Ticks in Colorado Dangerous for Pets

  • American dog tick (rare)
  • Brown dog tick
  • Lone star tick (rare)
  • Rocky Mountain wood tick

Tick-Borne Diseases Found in Colorado

  • Colorado tick fever (rare)
  • Ehrlichiosis
  • Rocky Mountain spotted fever
  • Tick paralysis
  • Tularemia

Ticks in Hawaii

With its sun-soaked beaches, volcanic mountains, and stunning waterfalls, the Aloha state has much to offer you and your adventure-loving pet. While ticks are relatively rare in Hawaii, it is still possible for your pet to get them, especially as people move other pets and livestock into the state. 

According to the Hawaii Department of Health, the tick you need to be mindful of is the brown dog tick. Other tick species, including the American dog tick and the lone star tick, have been found on Hawaii, but these instances are incredibly rare. 

Types of Ticks in Hawaii Dangerous for Pets

  • Brown dog tick

Tick-Borne Diseases Found in Hawaii

  • Ehrlichiosis
  • Rocky Mountain spotted fever (rare)

Ticks in Idaho

Idaho is a great place for pets. There are pet-friendly restaurants, parks for unleashed play, and plenty of hiking trails for your dog — or cat — to explore the great outdoors. But you can also find at least three different types of ticks in Idaho, according to CDC data: the brown dog tick, American dog tick, and the Rocky mountain wood tick. American dog ticks can be found in areas of long grass and low-lying brush, brown dog ticks can be found in homes and dog kennels, and Rocky mountain wood ticks can be found along trails, grasslands, and lightly wooded areas.

Although rarer, Western blacklegged ticks — a tick known to carry Lyme disease — have also been found in parts of Northern Idaho, according to the University of Idaho. Pets can pick them up in grass, brushland, along trails, or even semi-rural or suburban areas where wild animals like deer — which are known to carry the ticks — are present. Western blacklegged ticks are very small and seem to know how to hide in your dog’s fur, making it really difficult to find them.

Types of Ticks in Idaho Dangerous for Pets

  • American dog tick
  • Brown dog tick
  • Rocky mountain wood tick
  • Western blacklegged tick

Tick-Borne Diseases Found in Idaho

  • Ehrlichiosis
  • Lyme disease
  • Rocky Mountain spotted fever
  • Tularemia

Ticks in Montana

With its mountains, rivers, and prairies, Montana is the perfect state to enjoy the outdoors with your furry friend. But you should know that ticks in Montana can be found along streams or rivers, or in sagebrush flats, grassy meadows, wetlands or woods. Other ticks are found in indoor environments like homes, kennels or sheds. 

There are at least four ticks known to affect companion animals in Montana, all of which can cause various tick-borne diseases. But luckily, Lyme disease is not one of them. The only incidences of Lyme disease in pets are believed to have originated in other states.

Types of Ticks in Montana Dangerous for Pets

  • American dog tick
  • Brown dog tick (rare)
  • Rocky Mountain wood tick
  • Winter tick (rare)

Tick-Borne Diseases Found in Montana

  • Anaplasmosis (rare)
  • Colorado tick fever (rare)
  • Ehrlichiosis 
  • Rocky Mountain spotted fever 
  • Tick paralysis
  • Tularemia

Ticks in Nevada

Nevada is famous for the city of Las Vegas, but there is also a trove of natural attractions you can explore with your furry friend — from canyons to lakes to wilderness areas. Nevada’s dry climate means that ticks aren’t as prevalent here as they are in neighboring coastal states like California and Oregon. But this doesn’t mean that they’re not around. 

According to the CDC, four different disease-harboring ticks that affect companion dogs (as well as people) can be found in the state. What’s more, ticks are present in Nevada year round, which means that your pet may need year-round protection. 

Types of Ticks in Nevada Dangerous for Pets

  • American dog tick (rare)
  • Brown dog tick
  • Rocky Mountain wood tick
  • Western blacklegged tick

Tick-Borne Diseases Found in Nevada 

  • Anaplasmosis
  • Ehrlichiosis
  • Lyme disease (rare)
  • Rocky Mountain spotted fever
  • Tularemia

Ticks in New Mexico

New Mexico is a state with a dry, temperate climate that is full of parks, trails, and campgrounds for you to explore with your pet. But like many parts of the U.S., ticks are on the rise in New Mexico. Data compiled by the CDC indicates that there are two main ticks to watch out for: the brown dog tick and the Rocky Mountain tick. There are also reports of lone star ticks appearing in the state.

Types of Ticks in New Mexico Dangerous for Pets

  • Brown dog tick (rare)
  • Lone star tick (rare)
  • Rocky Mountain wood tick

Tick-Borne Diseases Found in New Mexico

  • Anaplasmosis
  • Colorado tick fever
  • Ehrlichiosis
  • Lyme disease 
  • Rocky Mountain spotted fever
  • Tick paralysis
  • Tularemia

Ticks in Oregon

With its mild and cool climate, you can explore Oregon’s many state parks, beaches, and wilderness areas year round. However, ticks could pose a problem for you and your pet at any time of the year. Reports also suggest that ticks are expanding their range in Oregon due to warmer weather.

Dr. Jensen says that pet parents in states like Oregon should be aware of the local risks and implement preventative measures. “Regular tick checks, repellents, and veterinary-approved preventatives are crucial for reducing the risk of tick-borne diseases,” she says.

Types of Ticks in Oregon Dangerous for Pets

  • American dog tick
  • Pacific Coast tick
  • Rocky Mountain wood tick
  • Western blacklegged tick

Tick-Borne Diseases Found in Oregon

  • Colorado tick fever (rare)
  • Lyme disease
  • Rocky Mountain spotted fever
  • Tick paralysis
  • Tularemia

Ticks in Utah

Utah is a land-locked state with dozens of parks, trails, and campgrounds you can explore with your furry friend. While parasites tend not to be a problem during the state’s snow-packed winters, you need to be mindful of ticks, fleas, and the mosquitoes that cause heartworm disease when the temperatures rise. 

Utah State University indicates that the most common tick people and their pets encounter in Utah is the Rocky Mountain wood tick, which can transmit diseases like the Colorado tick fever. 

Types of Ticks in Utah Dangerous for Pets

  • Brown dog tick
  • Rocky Mountain wood tick
  • Western blacklegged tick

Tick-Borne Diseases Found in Utah

  • Colorado tick fever 
  • Lyme disease (rare in pets who have not left Utah)
  • Rocky Mountain spotted fever 
  • Tick paralysis
  • Tick-borne relapsing fever 
  • Tularemia

Ticks in Washington

Washington state is a great place to live or visit if you have an adventure-loving pet. This Pacific Northwest state has dozens of pet-friendly parks, trails, and beaches you can explore with your furry friend. 

Ticks can be found all over Washington state, and they can affect your dog or cat at any time of the year. Your pet is most likely to pick one up when exploring the outdoors — from trails to grassy meadows to wooded areas frequented by other wildlife. 

Types of Ticks in Washington Dangerous for Pets

  • Brown dog tick
  • Rocky Mountain wood tick
  • Western blacklegged tick

Tick-Borne Diseases Found in Washington

  • Anaplasmosis
  • Ehrlichiosis
  • Lyme disease
  • Rocky Mountain spotted fever
  • Tick paralysis
  • Tick-borne relapsing fever
  • Tularemia

Ticks in Wyoming

Wyoming has some of the nation’s most picturesque wilderness areas, and you can explore many of these places with your dog or cat. However, you should know that you can encounter ticks at nearly every part of the year in the state, according to the Wyoming Department of Health. There are at least three types of ticks that can affect your pet in Wyoming, the most common one being the Rocky Mountain wood tick.

Types of Ticks in Wyoming Dangerous for Pets

  • American dog tick
  • Brown dog tick
  • Rocky Mountain wood tick

Tick-Borne Diseases Found in Wyoming

  • Ehrlichiosis (rare)
  • Colorado tick fever (rare)
  • Rocky Mountain spotted fever
  • Tularemia

Living in the West: Protecting Your Pet From Parasites

A pet cat sits by a screened door

So, how does one protect their pets from parasites in the western U.S. states, especially if they want to spend a lot of time outside? Dr. Jensen says pet parents should “work with veterinarians to establish parasite prevention plans tailored to their specific location and pet’s lifestyle.”

“Regular veterinary check-ups and preventive medications are crucial to safeguarding pets from these parasites,” Dr. Jensen adds.

In addition to check-ups and medications, Dr. Grewal suggests keeping your yard clean and reducing possible mosquito breeding sites, and minimizing your pets’ exposure to high-risk areas, especially during peak parasite season in your state. 

Dr. Pulaski says it’s also important for all pets to be tested and protected against parasites, no matter how prevalent parasites are said to be in their state. However, she acknowledged that it is not always financially possible for every pet parent to give their dog or cat year-round protection.

“If doing full protection every day of the year is not available, I really think pet owners should talk to their vet about what is the highest risk in their area for this time of the year or this season,” Dr. Pulaski says. “This is how things like prevalence data and forecast maps can really help.”


References

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Authored by

Elizabeth Claire Alberts

Elizabeth is an American journalist currently based in Belgium. She spent three years working as a staff writer at The Dodo, where she covered stories on pet rescues, pet health, animal rights, and the human-animal connection. She now works as a senior staff writer at Mongabay, covering ocean, climate and wildlife issues, and does freelance writing for various media outlets.

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Reviewed by

Sarah J. Wooten, DVM

Dr. Sarah Wooten is a well known international influencer in the veterinary and animal health care spaces. She has 16 years experience in private practice and over 10 years experience in veterinary media work, and is a certified veterinary journalist.

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