Tick-Borne Diseases in Dogs: Lyme, Ehrlichiosis & More

Tick-borne diseases represent one of the most significant and growing threats to canine health worldwide. When an infected tick attaches to your dog and begins feeding, it can transmit dangerous pathogens — bacteria, protozoa, or viruses — directly into your dog's bloodstream. The transmission doesn't happen instantly; most tick-borne pathogens require the tick to be attached for 24 to 48 hours before transmission occurs, which is why prompt tick removal is so critical. However, some diseases like Powassan virus can be transmitted in as little as 15 minutes of attachment.

"Tick-borne diseases are among the most under-diagnosed conditions in veterinary medicine. Many of these infections have vague early symptoms — lethargy, mild fever, reduced appetite — that owners easily attribute to a bad day. By the time more specific signs develop, the disease may have progressed significantly. I always tell owners: if your dog has had tick exposure and seems even slightly off, get a blood test." — Dr. Sarah Chen, DVM

The risk landscape has shifted dramatically over the past two decades. Climate change has expanded tick habitats into regions previously considered safe, and milder winters mean ticks remain active for longer periods — in many areas, year-round. The blacklegged tick (deer tick), the American dog tick, the brown dog tick, and the lone star tick are the primary species responsible for transmitting disease to dogs in North America, while Ixodes ricinus is the main culprit across Europe and the UK. Each species carries different pathogens, meaning your dog's risk profile depends partly on geography.

What makes tick-borne diseases particularly insidious is that dogs can be infected with multiple pathogens simultaneously — a phenomenon called co-infection. A single tick may carry more than one pathogen, or a dog may be bitten by multiple infected ticks over time. Co-infections are harder to diagnose and treat because symptoms overlap and can mask one another. Understanding the major tick-borne diseases, their symptoms, and the importance of proper tick removal is essential for every dog owner, regardless of where you live.

Lyme disease, caused by the spirochete bacterium Borrelia burgdorferi, is the most prevalent tick-borne disease affecting dogs in the Northern Hemisphere. It is transmitted primarily by blacklegged ticks (Ixodes scapularis in eastern North America and Ixodes pacificus on the West Coast) and by Ixodes ricinus in Europe. The bacterium requires approximately 36 to 48 hours of tick attachment to transfer to the host, making daily tick checks a powerful preventive measure.

Only about 5 to 10 per cent of dogs exposed to Borrelia burgdorferi actually develop clinical disease, but when they do, the consequences can be severe. Symptoms typically appear two to five months after the tick bite, making it difficult for owners to connect the illness to a specific exposure event. The hallmark signs include shifting-leg lameness — your dog may limp on one leg, seem to improve, and then begin limping on a different leg. This occurs because the bacteria trigger joint inflammation that moves between joints. Affected dogs often have swollen, warm, and painful joints, particularly the larger joints like the elbows, shoulders, and stifles.

Beyond lameness, dogs with Lyme disease commonly show generalised signs: fever (often 103 to 105 degrees Fahrenheit), lethargy, reduced appetite, and swollen lymph nodes. The most serious complication is Lyme nephritis — a potentially fatal kidney disease that causes protein loss through the kidneys, leading to swelling of the limbs and abdomen, vomiting, weight loss, and eventually kidney failure. Certain breeds, including Labrador Retrievers, Golden Retrievers, and Bernese Mountain Dogs, appear predisposed to this devastating complication.

Diagnosis involves a combination of clinical signs, tick exposure history, and blood testing. The commonly used SNAP 4Dx test can detect antibodies to Borrelia burgdorferi in the clinic within minutes. However, a positive result only confirms exposure — not necessarily active infection. Your vet may recommend a quantitative C6 antibody test (Lyme Quant C6) to differentiate between past exposure and active infection. Treatment typically involves a 30-day course of the antibiotic doxycycline, which is highly effective when started early. Dogs usually show improvement within 24 to 48 hours of beginning antibiotics, though the full course must be completed to prevent relapse.

Ehrlichiosis and anaplasmosis are closely related tick-borne diseases caused by bacteria that invade and destroy specific types of blood cells. Canine monocytic ehrlichiosis (CME), caused by Ehrlichia canis, is transmitted by the brown dog tick and targets white blood cells called monocytes. Canine granulocytic anaplasmosis, caused by Anaplasma phagocytophilum, is spread by blacklegged ticks and attacks a different type of white blood cell — granulocytes. A related organism, Anaplasma platys, targets platelets and causes cyclic thrombocytopenia.

Ehrlichiosis progresses through three distinct phases. The acute phase begins one to three weeks after infection and causes fever, lethargy, swollen lymph nodes, loss of appetite, and sometimes nasal discharge or difficulty breathing. Many dogs clear the infection during this phase with appropriate treatment. Without treatment, however, the disease enters a subclinical phase lasting weeks to months where the dog appears outwardly normal but the bacteria persist in the spleen. Some dogs remain in this phase indefinitely; others progress to the chronic phase, which is far more serious. Chronic ehrlichiosis causes severe bone marrow suppression, leading to dangerous drops in all blood cell types — a condition called pancytopenia. Dogs may develop uncontrolled bleeding, secondary infections, chronic weight loss, and swollen limbs.

Anaplasmosis tends to present more acutely. Dogs typically develop sudden-onset fever, joint pain, lethargy, and loss of appetite within one to two weeks of the infecting tick bite. Vomiting, diarrhoea, coughing, and laboured breathing may also occur. Blood work commonly reveals low platelet counts (thrombocytopenia), which can lead to bruising or small pinpoint bleeding spots on the gums and skin. Fortunately, most dogs respond rapidly to treatment.

Both diseases are diagnosed through a combination of clinical signs, blood work abnormalities, and specific antibody testing. The SNAP 4Dx Plus test screens for both Ehrlichia and Anaplasma antibodies alongside Lyme disease and heartworm. Treatment for both conditions is doxycycline, typically prescribed for 28 days. Prognosis for acute and subclinical cases is excellent, but chronic ehrlichiosis carries a more guarded outlook. This is why consistent year-round tick prevention is so vital — catching these diseases early or, better yet, preventing tick bites entirely makes all the difference.

Rocky Mountain Spotted Fever (RMSF), caused by Rickettsia rickettsii, is one of the most acute and potentially deadly tick-borne diseases in dogs. Despite its name, RMSF occurs throughout the Americas — not just in the Rocky Mountain region. It is transmitted by the American dog tick, the brown dog tick, and the Rocky Mountain wood tick. Unlike Lyme disease, RMSF can be transmitted within just a few hours of tick attachment, making rapid removal even more urgent.

RMSF causes widespread inflammation of small blood vessels (vasculitis), which leads to a range of severe symptoms. Dogs typically develop sudden high fever (104 to 106 degrees Fahrenheit), severe lethargy, loss of appetite, joint and muscle pain, and swollen lymph nodes within two to fourteen days of the tick bite. Skin lesions — including reddened, bruised-looking patches or small haemorrhages on the gums, whites of the eyes, and skin — are classic signs. Neurological symptoms such as wobbliness, head tilt, and seizures can develop if the blood vessels in the brain become inflamed. Without prompt treatment, RMSF can cause organ failure and death within days. Fortunately, dogs treated early with doxycycline typically improve dramatically within 24 to 72 hours.

Babesiosis is a protozoal disease caused by Babesia species that invade and destroy red blood cells, leading to haemolytic anaemia. Dogs may present with pale gums, dark-coloured urine, weakness, jaundice (yellowing of the skin and eyes), and fever. Treatment depends on the species involved and may include antiprotozoal medications such as imidocarb dipropionate or a combination of atovaquone and azithromycin. Severe cases may require blood transfusions.

Other notable tick-borne threats include hepatozoonosis (contracted when dogs ingest infected ticks), tick paralysis (caused by a neurotoxin in tick saliva rather than an infectious organism), and bartonellosis. Tick paralysis is especially alarming — a single attached female tick can cause progressive weakness starting in the hind legs and ascending toward the head, potentially leading to respiratory failure. The good news is that symptoms resolve rapidly once the tick is found and removed. Given the wide range of serious diseases ticks can transmit, maintaining a robust preventative care schedule that includes year-round tick control is one of the best investments you can make in your dog's health.

If you suspect your dog may have a tick-borne disease — whether you found an engorged tick, noticed unexplained lameness, or your dog has a persistent fever — the first step is a thorough veterinary examination. Your vet will start by assessing vital signs, checking for enlarged lymph nodes, examining joints for swelling or pain, and inspecting gums for pallor or petechiae (tiny red bleeding spots). A complete history of tick exposure, travel to endemic areas, and current preventive medications is essential for guiding the diagnostic workup.

Blood work is the cornerstone of tick-borne disease diagnosis. A complete blood count (CBC) often reveals hallmark changes: low platelet counts are common in ehrlichiosis, anaplasmosis, and RMSF; low red blood cell counts suggest babesiosis or chronic ehrlichiosis; and elevated white blood cell counts may indicate an active infection. A chemistry panel helps assess kidney and liver function, which can be compromised in several tick-borne diseases. Urinalysis is particularly important if Lyme disease is suspected, as protein in the urine can signal the onset of Lyme nephritis.

Point-of-care antibody tests such as the SNAP 4Dx Plus provide rapid screening for Lyme disease, Ehrlichia, and Anaplasma antibodies in just eight minutes. For more detailed or confirmatory testing, your vet may send blood to an external laboratory for PCR (polymerase chain reaction) testing, which detects the actual DNA of the pathogen and can identify active infections. Specific quantitative antibody levels — such as the Lyme Quant C6 — help distinguish between old exposure and current disease requiring treatment.

Treatment for most bacterial tick-borne diseases centres on antibiotics, with doxycycline being the first-line choice for Lyme disease, ehrlichiosis, anaplasmosis, and RMSF. The standard course is 28 to 30 days, and it's critical to complete the entire prescription even if your dog improves quickly. Supportive care may include anti-inflammatory medications for joint pain, anti-nausea drugs, IV fluids for dehydrated patients, and blood transfusions for dogs with severe anaemia. Babesiosis requires different drugs — typically imidocarb injections or a combination of atovaquone and azithromycin. Follow-up blood work four to six weeks after treatment completion helps confirm the infection has been cleared. Dogs that have recovered from a tick-borne illness should remain on vigilant parasite prevention programs to prevent reinfection.

Preventing tick-borne diseases is far easier, safer, and less expensive than treating them. A multi-layered approach — combining tick-repelling products, environmental management, daily tick checks, and smart outdoor habits — gives your dog the best protection. The single most effective step is using a veterinarian-recommended tick preventative consistently and year-round. Even in colder climates, ticks can become active on any day the temperature rises above 4 degrees Celsius (about 40 degrees Fahrenheit), and mild winters increasingly mean ticks never fully enter dormancy.

Modern tick preventatives fall into three main categories: oral medications (like fluralaner, sarolaner, and afoxolaner), topical spot-on treatments (such as fipronil or permethrin-based products), and medicated tick collars (like the seresto collar). Oral preventatives have become increasingly popular because they provide systemic protection — when a tick bites a treated dog, it ingests the active ingredient and dies, typically before it can transmit pathogens. Topical treatments repel and kill ticks on contact, while collars release active ingredients across the skin over several months. Your vet can help you choose the best option based on your dog's health, lifestyle, and risk factors.

Environmental management plays an important supporting role. In your garden, keep grass trimmed short, remove leaf litter and brush piles, and create a buffer zone of gravel or wood chips between wooded areas and your lawn. Ticks thrive in shaded, humid environments, so reducing these habitats around your home minimises the tick population near your dog's main living space. When walking your dog in wooded or grassy areas, try to stick to cleared paths and avoid letting your dog roam into tall vegetation where questing ticks wait on blade tips and leaf edges.

Daily tick checks should become a non-negotiable part of your routine, especially during peak tick season (spring through autumn in most regions). Run your hands systematically over your dog's entire body, paying special attention to the ears, around the eyes, under the collar, between the toes, around the tail base, and in the groin area — ticks gravitate toward warm, hidden spots. If you find a tick, remove it promptly and correctly using fine-tipped tweezers or a tick removal tool. Finally, discuss the Lyme disease vaccine with your vet. While not effective against other tick-borne diseases, the Lyme vaccine can provide an additional layer of protection for dogs living in or travelling to high-risk areas. Combining these strategies with a broader parasite awareness plan will significantly reduce your dog's chances of contracting a tick-borne disease.