Your Dog’s World Is Your World Too: Zoonotic and Vector-Borne Diseases Every Dog Owner Needs to Know.
A One Health Guide to Protecting Your Dog — and Your Family
Table of Contents
1. The Backyard Is Not as Safe as You Think
2. What Is One Health — and Why Does It Matter for Dog Owners?
3. The Tick: A Tiny Vector with an Outsized Threat
4. Lyme Disease: The Most Recognized Tick-Borne Threat
5. Rocky Mountain Spotted Fever: Deadly and Deceptive
6. Ehrlichiosis and Anaplasmosis: The Overlooked Pair
7. Leptospirosis: The Disease Hiding in Puddles
8. Heartworm Disease: A Mosquito-Borne Zoonotic Concern
9. Brucellosis: The Underrecognized Threat
10. Your Dog as a Sentinel: An Early Warning System for Human Health
11. Climate Change Is Expanding the Threat
12. What You Can Do: Vaccines, Prevention, and Partnership
1. The Backyard Is Not as Safe as You Think
Picture a perfect Saturday morning. You open the back door, and your dog bolts outside, nose to the ground, tail spinning like a helicopter. He rolls in the grass, splashes through a puddle left by last night’s rain, and disappears into the shrubs at the edge of the yard. You smile. This is what dogs are made for.
But here’s what you might not see: the deer tick clinging to a blade of grass at the edge of the lawn, waiting for a warm body to brush past. The standing water in the flower pot where mosquito larvae are hatching. The trail of urine left by a raccoon that passed through the yard at 3 a.m., carrying bacteria that can survive in moist soil for weeks.
Your dog’s world — the yard, the park, the hiking trail, the puddle — is also a landscape of invisible biological risk. And because dogs live so close to us, sharing our beds, our couches, and our daily routines, the diseases they encounter in that world can become our diseases too.
This is not a reason to keep your dog indoors or to live in fear. It is a reason to be informed. The good news is that many of the most serious zoonotic and vector-borne diseases that affect dogs — and the people who love them — are preventable. Some can be addressed with vaccines. Others require year-round parasite prevention. All of them benefit from a relationship with a veterinarian who understands the risks in your specific region.
This blog post is your guide to understanding those risks, recognizing the diseases, and taking the steps that protect your whole family — the two-legged and four-legged members alike.
2. What Is One Health — and Why Does It Matter for Dog Owners?
Before we dive into specific diseases, it helps to understand the framework that scientists, veterinarians, and public health officials use to think about the connection between animal health and human health. That framework is called One Health.
“One Health is an integrated, unifying approach that aims to sustainably balance and optimize the health of people, animals and ecosystems. It recognizes that the health of humans, domestic and wild animals, plants, and the wider environment are closely linked and interdependent.” — World Health Organization [1]
The CDC defines One Health as “a collaborative, multisectoral, and transdisciplinary approach — working at the local, regional, national, and global levels — with the goal of achieving optimal health outcomes recognizing the interconnection between people, animals, plants, and their shared environment” [2].
For dog owners, One Health is not an abstract concept. It plays out every time your dog comes inside after a walk, every time a tick drops off his coat onto your carpet, every time he drinks from a stream on a hiking trail. The health decisions you make for your dog — whether to vaccinate, whether to use parasite prevention, whether to schedule that annual wellness exam — are also health decisions for your family.
Approximately 60% of all known infectious diseases in humans are zoonotic in origin, meaning they originated in or are shared with animals. And dogs, as our closest animal companions, are uniquely positioned at the intersection of human and animal health. They go where we go, live where we live, and encounter the same environmental risks we do — often before we do.
3. The Tick: A Tiny Vector with an Outsized Threat
Ticks are not insects — they are arachnids, more closely related to spiders and scorpions than to flies or mosquitoes. And unlike many other parasites, they are remarkably efficient disease vectors, capable of transmitting multiple pathogens in a single bite.
In the United States, the tick species most relevant to dog owners include:
• The black-legged tick (Ixodes scapularis), also called the deer tick — the primary vector for Lyme disease, anaplasmosis, and babesiosis in the Northeast and Upper Midwest
• The American dog tick (Dermacentor variabilis) — a primary vector for Rocky Mountain spotted fever
• The brown dog tick (Rhipicephalus sanguineus) — found worldwide, capable of completing its entire life cycle indoors, and a vector for Rocky Mountain spotted fever and ehrlichiosis
• The lone star tick (Amblyomma americanum) — a vector for ehrlichiosis and other pathogens, increasingly common in the Southeast and South Central states
• The Asian longhorned tick (Haemaphysalis longicornis) — an invasive species whose full pathogen transmission potential in the U.S. is still being studied [3]
What makes ticks particularly dangerous is their stealth. A tick bite is often painless. The tick may feed for several days before dropping off, and many people — and dogs — never notice the attachment. By the time symptoms appear, the pathogen has already been transmitted.
Dogs are exposed to ticks far more frequently than most people realize. Every walk through tall grass, every romp in a wooded area, every sniff along a hedgerow is a potential tick encounter. And because dogs cannot tell us when they feel unwell, tick-borne diseases can progress significantly before they are diagnosed.
4. Lyme Disease: The Most Recognized Tick-Borne Threat
Lyme disease is caused by the spirochete bacterium Borrelia burgdorferi, transmitted primarily by the black-legged tick. It is one of the most common vector-borne diseases in both dogs and humans in the United States, and its geographic range is expanding.
According to 2024 data from the Companion Animal Parasite Council (CAPC), more than 7% of dogs tested in Wisconsin were positive for Lyme disease exposure, and over 10% of dogs tested in parts of New England showed positive results [3]. These are not small numbers. In high-risk areas, Lyme disease is not a rare event — it is a routine threat.
What It Looks Like in Dogs
In dogs, Lyme disease can be tricky to identify. Many infected dogs never show obvious symptoms, yet they carry the bacteria and can develop complications over time. When symptoms do appear, they typically include:
• Fever and lethargy
• Loss of appetite
• Shifting leg lameness — the dog may limp on one leg, then another, seemingly at random
• Swollen lymph nodes
• In severe cases, kidney disease (Lyme nephritis), which can be fatal
The Human Connection
Dogs do not directly transmit Lyme disease to humans. However, they serve as tick transport vehicles. A dog that walks through tick-infested areas can carry ticks into the home, where those ticks may then attach to human family members. A dog with a high tick burden is a signal that the surrounding environment has a high tick burden — and that human family members are also at risk.
Prevention: The Vaccine Advantage
Lyme disease is one of the few tick-borne diseases for which a vaccine is available for dogs. The CAPC recommends vaccination against Borrelia burgdorferi in all dogs living in or traveling to endemic or emerging areas [4]. Combined with year-round tick prevention products, vaccination provides a powerful two-layer defense.
5. Rocky Mountain Spotted Fever: Deadly and Deceptive
Despite its name, Rocky Mountain spotted fever (RMSF) is most commonly reported east of the Mississippi River, with more than 60% of cases concentrated in North Carolina, Oklahoma, Arkansas, Tennessee, and Missouri [5]. It is caused by the bacterium Rickettsia rickettsii and is transmitted by the American dog tick, the Rocky Mountain wood tick, and the brown dog tick.
RMSF is one of the most severe tick-borne diseases in the United States. Without prompt treatment, it can be fatal in both dogs and humans. The case fatality rate in untreated humans can exceed 20%, and even with treatment, outcomes depend heavily on how quickly the diagnosis is made.
What Makes RMSF Particularly Dangerous
The classic triad of RMSF — fever, headache, and rash — does not always appear together, and the rash may not develop until several days into the illness, if at all. This makes early diagnosis challenging. In dogs, symptoms include fever, loss of appetite, vomiting, diarrhea, muscle pain, and in severe cases, neurological signs and hemorrhage.
The brown dog tick is of particular concern because, unlike most tick species, it can complete its entire life cycle indoors. This means that a home with an infested dog can become a year-round reservoir for RMSF-carrying ticks — a scenario that has been associated with unusually high incidence and case fatality rates in parts of Arizona and northern Mexico [5].
Prevention
There is currently no vaccine for RMSF in dogs or humans. Prevention relies entirely on tick control — using veterinarian-recommended tick prevention products on your dog year-round, performing thorough tick checks after outdoor activities, and treating your home and yard if an infestation is suspected.
6. Ehrlichiosis and Anaplasmosis: The Overlooked Pair
Ehrlichiosis and anaplasmosis are two distinct tick-borne diseases that are often discussed together because they share similar transmission routes, clinical presentations, and prevention strategies. Both are caused by bacteria that infect white blood cells, and both can affect dogs and humans.
Ehrlichiosis
Canine ehrlichiosis is caused primarily by Ehrlichia canis, transmitted by the brown dog tick. It is widespread across North and South America, Europe, Asia, and Africa. In the United States, states with the highest proportion of positive dogs include Missouri (11%) and Arkansas (17%) [3].
The disease progresses through three phases: an acute phase with fever, lethargy, and swollen lymph nodes; a subclinical phase where the dog appears to recover but the bacteria persist; and a chronic phase that can involve severe anemia, bleeding disorders, and neurological signs. The chronic phase can be life-threatening and is much harder to treat than early-stage disease.
Importantly, new species of Ehrlichia have been identified in parts of Wisconsin and Minnesota, underscoring the importance of testing even in regions not traditionally considered high-risk [3].
Anaplasmosis
Anaplasmosis in dogs is caused by Anaplasma phagocytophilum, transmitted by the same black-legged tick that carries Lyme disease. This means that in endemic areas, a single tick bite can potentially transmit both Lyme disease and anaplasmosis simultaneously.
Clinical signs in dogs include fever, lethargy, low platelet count (which can cause bleeding), and low white blood cell count. In humans, anaplasmosis presents similarly — with fever, headache, muscle aches, and malaise — and can be severe in immunocompromised individuals.
2024 CAPC data showed that trends in Anaplasma exposure in dogs continued to show increasing prevalence beyond historically high-risk areas, expanding along the West Coast and moving southward across the country [3]. Neither ehrlichiosis nor anaplasmosis has a vaccine available for dogs, making tick prevention the cornerstone of protection.
7. Leptospirosis: The Disease Hiding in Puddles
Not all zoonotic diseases that threaten dogs are vector-borne. Leptospirosis is a bacterial disease caused by Leptospira bacteria, and it spreads through a very different route: contaminated water and soil.
The bacteria are shed in the urine of infected animals — including wildlife such as raccoons, opossums, deer, and rodents — and can survive in fresh water and moist soil for weeks to months in warm conditions [6]. When a dog drinks from a puddle, wades through a stream, or sniffs contaminated soil, the bacteria can enter through mucous membranes or small cuts in the skin.
A Truly Global Zoonosis
Leptospirosis is among the leading zoonotic disease causes of illness worldwide. An estimated 1 million cases occur globally each year, resulting in nearly 60,000 deaths [6]. The disease is significantly underdiagnosed and underreported, meaning the true burden is likely even higher.
In dogs, leptospirosis can cause kidney failure, liver failure, and in severe cases, death. In humans, the disease presents with fever, muscle aches, headache, and vomiting — symptoms that can easily be mistaken for influenza. Without treatment, it can progress to kidney failure, jaundice, respiratory distress, and meningitis. In 5–10% of severe cases, multiorgan failure and death can occur [6].
A 2025 systematic review and meta-analysis published in Open Forum Infectious Diseases highlighted the critical need for a One Health approach to leptospirosis, noting positive associations between human and animal seroprevalences and the link between environmental positivity and domestic animal infection rates [7].
Urban Dogs Are Not Exempt
Many dog owners assume leptospirosis is a rural disease — something that affects farm dogs or hunting dogs, not city pets. This is a dangerous misconception. Urban environments, with their populations of rats and other wildlife, can be significant sources of Leptospira contamination. A dog that walks through a city park, sniffs a storm drain, or drinks from a puddle after heavy rain is at risk.
The Vaccine Option
A vaccine for leptospirosis is available for dogs and is recommended by the CAPC for dogs with potential exposure to contaminated water or wildlife. Given the broad geographic distribution of the disease and the difficulty of predicting wildlife movement, many veterinarians now recommend the leptospirosis vaccine as a core or near-core vaccine for dogs in a wide range of environments.
8. Heartworm Disease: A Mosquito-Borne Zoonotic Concern
Heartworm disease is caused by Dirofilaria immitis, a parasitic roundworm transmitted through the bites of infected mosquitoes. Dogs are the primary natural host, and in untreated dogs, adult worms can grow up to 12 inches long and live in the heart, lungs, and associated blood vessels, causing severe lung disease, heart failure, and death.
Heartworm disease has seen persistently high levels throughout the southern United States, with some of 2024’s highest prevalence — 3–5% of all dogs tested — recorded along the Gulf Coast [3]. The incidence continues to increase in the mid-Atlantic region, pushing northward into the densely populated Northeast.
The Zoonotic Dimension
While dogs are the primary host, Dirofilaria immitis can infect humans. Human dirofilariasis is considered rare, but it is not negligible. When an infected mosquito bites a human, the larvae can migrate to the lungs, where they form coin-shaped lesions that are often discovered incidentally on chest X-rays and can be mistaken for lung tumors [8]. The CDC notes that the main natural hosts for D. immitis are dogs and wild canids, making infected dogs a reservoir that sustains the mosquito transmission cycle in a community.
Prevention Is the Only Practical Strategy
There is no vaccine for heartworm disease. Prevention relies on monthly or long-acting preventive medications prescribed by a veterinarian. The CAPC recommends year-round heartworm prevention for all dogs, regardless of geographic location, because mosquito activity is increasingly year-round in many parts of the country due to climate change [4].
9. Brucellosis: The Underrecognized Threat
Brucellosis in dogs is caused by Brucella canis, a bacterium that is maintained primarily in domestic dogs. It is a disease that many dog owners have never heard of — yet it is more common than most people realize, and it carries real zoonotic risk.
A 2026 review published in the journal One Health estimated a pooled global canine prevalence of 7.96%, with substantially higher values in breeding, kennel, and shelter settings [9]. In dogs, infection causes reproductive failure, persistent bacteremia, and a high proportion of asymptomatic carriers capable of intermittent shedding — meaning an infected dog may look and act completely healthy while still being capable of spreading the bacteria.
Human Risk
Human infection with B. canis is infrequently reported but likely underestimated. A scoping review found that 80% of human infections with known exposure were associated with direct dog contact [9]. In humans, brucellosis presents with fever, chills, malaise, swollen lymph nodes, and splenomegaly — symptoms that are nonspecific and easily attributed to other causes, contributing to underdiagnosis.
People at highest risk include dog breeders, veterinary professionals, shelter workers, and anyone who handles reproductive fluids or tissues from infected dogs. The CDC notes that brucellosis in dogs cannot be cured — infected dogs remain carriers for life [10].
What Dog Owners Should Know
There is no vaccine for B. canis in dogs. If you are adopting a dog from a shelter, rescue, or breeder, ask whether the dog has been tested for brucellosis. If you are a breeder, testing all dogs before breeding is essential. If your dog tests positive, work closely with your veterinarian and local health department to understand the implications for your household.
10. Your Dog as a Sentinel: An Early Warning System for Human Health
One of the most powerful — and underappreciated — aspects of the One Health relationship between dogs and humans is the role dogs play as sentinel species. A sentinel species is one that, by virtue of its biology and behavior, detects environmental health threats before humans do.
Dogs are ideal sentinels for vector-borne and zoonotic diseases for several reasons:
• They spend more time outdoors than most humans and in closer contact with the ground, vegetation, and wildlife habitats where vectors live
• They are tested regularly by veterinarians, generating surveillance data that can reveal disease trends in a community
• They share the same geographic environment as their owners, meaning their exposure reflects human exposure risk
• They often develop disease before their human companions, providing an early warning signal
Research published in Scientific Reports demonstrated that pet insurance claims for vector-borne diseases in dogs can be used to predict the occurrence of those same diseases in humans in the same geographic areas [11]. In other words, when dogs in a community start testing positive for Lyme disease or anaplasmosis at higher rates, it is a signal that human risk in that community is also rising.
When your dog tests positive for a tick-borne disease, it is not just information about your dog. It is information about your neighborhood, your yard, and your family’s risk.
This is why annual testing for vector-borne diseases in dogs is not just good veterinary medicine — it is a public health act. The data generated by routine veterinary testing contributes to surveillance systems that help track disease trends, identify emerging threats, and guide public health responses.
11. Climate Change Is Expanding the Threat
The geographic distribution of ticks, mosquitoes, and the diseases they carry is not static. Climate change is actively reshaping the landscape of vector-borne disease risk in the United States and around the world.
Warmer temperatures allow ticks to survive in regions that were previously too cold for them. Milder winters mean ticks remain active for longer periods of the year. Shifting rainfall patterns create new areas of standing water that support mosquito breeding. The CAPC’s 2024 Pet Parasite Forecast noted that climate change is a major driver of the continued expansion of heartworm, Lyme disease, ehrlichiosis, and anaplasmosis throughout the United States [12].
The black-legged tick, historically concentrated in the Northeast and Upper Midwest, has been documented expanding its range southward and westward. For the first time, the 2024 CAPC forecast included eastern Montana in its Lyme disease risk map. Anaplasmosis is showing increasing prevalence along the West Coast. Heartworm risk is pushing northward into the densely populated Northeast and into states like North and South Dakota and Montana [12].
Urbanization compounds the problem. When people build new neighborhoods or clear land, they often create ideal habitats for vectors and their wildlife hosts, while simultaneously bringing pets and people into closer contact with those vectors. Human travel and pet relocation for adoption further spread infected vectors or hosts to new areas.
The practical implication for dog owners is straightforward: the risk map is changing, and it is changing in the direction of greater risk for more dogs in more places. A dog owner in a region that was not historically considered high-risk for Lyme disease or heartworm may find that their veterinarian is now recommending vaccines or preventives that were not previously discussed. This is not alarmism — it is science.
12. What You Can Do: Vaccines, Prevention, and Partnership
The diseases described in this post can sound overwhelming. But the message is not one of helplessness — it is one of empowerment. There is a great deal you can do to protect your dog and your family, and most of it is straightforward.
Ask Your Veterinarian About Vaccines
Vaccines are available for two of the diseases discussed in this post: Lyme disease and leptospirosis. Both are highly effective when used as part of a comprehensive prevention strategy. Whether your dog needs these vaccines depends on factors including your geographic location, your dog’s lifestyle, and local disease prevalence. Your veterinarian is the best person to assess your dog’s individual risk and make a tailored recommendation.
Do not wait for your dog to show symptoms before having this conversation. Ask at your next wellness visit: “Is my dog at risk for Lyme disease or leptospirosis? Should we be vaccinating?”
Use Year-Round Parasite Prevention
For the diseases without vaccines — RMSF, ehrlichiosis, anaplasmosis, heartworm — year-round parasite prevention is the primary defense. The CAPC recommends year-round broad-spectrum parasite control with efficacy against heartworm, intestinal parasites, fleas, and ticks for all dogs [4]. There are many excellent products available — your veterinarian can help you choose the right combination for your dog’s lifestyle and your local risk profile.
Test Annually
Annual testing for heartworm and tick-borne diseases is recommended for all dogs. Testing serves two purposes: it detects disease early, when treatment is most effective, and it contributes to the community-level surveillance data that helps track disease trends. A simple blood test at your annual wellness visit can screen for heartworm, Lyme disease, ehrlichiosis, and anaplasmosis simultaneously.
Practice Environmental Awareness
• Perform thorough tick checks on your dog — and yourself — after every outdoor excursion
• Avoid letting your dog drink from standing water, puddles, or slow-moving streams
• Pick up dog feces promptly to reduce environmental contamination
• Be aware of wildlife activity in your area — raccoons, deer, and rodents are reservoirs for multiple zoonotic pathogens
• Wash your hands after handling your dog, especially after outdoor activities
Schedule Regular Wellness Visits
The CAPC recommends preventive physical examinations at least every 6 to 12 months for dogs [4]. These visits are not just about vaccines and parasite prevention — they are an opportunity for your veterinarian to assess your dog’s overall health, discuss regional disease risks, and catch problems early. Think of your veterinarian as a partner in One Health: someone who is protecting not just your dog, but your whole family.
A Final Word: Your Dog Is Counting on You
The diseases described in this post are real, they are present in communities across the United States, and their geographic reach is growing. But they are also, in large part, preventable. The tools exist: vaccines for Lyme disease and leptospirosis, year-round parasite prevention for the diseases without vaccines, annual testing to catch infections early, and a trusted veterinary partner to guide you through the decisions that are right for your dog and your region.
One Health is not a slogan. It is a reality that plays out every day in the relationship between you, your dog, and the world you share. When you protect your dog, you protect your family. When you vaccinate, you reduce the reservoir of disease in your community. When you test annually, you contribute to the surveillance data that helps scientists and public health officials track and respond to emerging threats.
The next time your dog bolts out the back door into the morning sun, tail spinning, nose to the ground — smile. And then make sure he’s protected for every adventure that follows.
Talk to your veterinarian today. Ask about vaccines for Lyme disease and leptospirosis. Ask about year-round parasite prevention. Ask about annual testing. Your dog — and your family — will thank you.
References
[1] World Health Organization. (2024). One Health. WHO Europe. https://www.who.int/europe/initiatives/one-health
[2] Centers for Disease Control and Prevention. (2025). About One Health. CDC. https://www.cdc.gov/one-health/about/index.html
[3] Lashnits, E. (2025). Annual Review: Vector-Borne Disease in 2024 and What To Expect in 2025. The Vetiverse. https://www.thevetiverse.com/en/latest/annual-review-vector-borne-disease-in-2024-and-what-to-expect-in-2025/
[4] Companion Animal Parasite Council. (2025). General Guidelines for Dogs and Cats. CAPC. https://capcvet.org/guidelines/general-guidelines/
[5] Centers for Disease Control and Prevention. (2024). Clinical Overview of Transmission and Epidemiology: Rocky Mountain Spotted Fever. CDC. https://www.cdc.gov/rocky-mountain-spotted-fever/hcp/clinical-overview/index.html
[6] Centers for Disease Control and Prevention. (2026). Clinical Overview of Leptospirosis. CDC. https://www.cdc.gov/leptospirosis/hcp/clinical-overview/index.html
[7] Antoniolli, A., Guis, H., Picardeau, M., Goarant, C., & Flamand, C. (2025). One Health Field Approach Applied to Leptospirosis: A Systematic Review and Meta-Analysis. Open Forum Infectious Diseases, 12(1), ofae757. https://academic.oup.com/ofid/article/12/1/ofae757/7934896
[8] Centers for Disease Control and Prevention. (2024). About Dirofilariasis. CDC. https://www.cdc.gov/dirofilariasis/about/index.html
[9] Storoni, C., et al. (2026). Brucella canis in dogs: An underrecognized zoonotic pathogen requiring a one health response. One Health, 23, 101506. https://pubmed.ncbi.nlm.nih.gov/42440889/
[10] Centers for Disease Control and Prevention. (2026). Brucellosis and Animals. CDC. https://www.cdc.gov/brucellosis/php/animal-health/index.html
[11] Nature Scientific Reports. (2025). Using pet insurance claims to predict occurrence of vector-borne and zoonotic disease in humans in the United States. Scientific Reports. https://www.nature.com/articles/s41598-025-99229-9
[12] American Veterinary Medical Association. (2024). CAPC forecasts continuing spread of parasitic diseases. AVMA. https://www.avma.org/news/capc-forecasts-continuing-spread-parasitic-diseases
