CONDITION
Lyme Disease (Borreliosis)
Lyme disease is an infection caused by bacteria of the Borrelia burgdorferi sensu lato group, transmitted when an infected tick feeds on a dog or cat for a prolonged period. The condition is named after a town in Connecticut where it was first recognised in people, and the bacteria are carried by Ixodes ticks in the UK and much of Europe. In pets, the infection can remain silent for weeks or months, or it may trigger signs that range from intermittent lameness and joint pain to more generalised illness. Many owners arrive at this page because their pet has been found to carry ticks after woodland walks, or because a limp has appeared and disappeared without obvious injury, or because a blood test has returned a positive result. Cats can test positive for antibodies, but it is not known whether the infection makes them ill. Dogs can develop shifting leg lameness, lethargy, or occasionally signs of kidney involvement. This page explores what Lyme disease can look like in dogs, how the bacteria behave once inside the body, the ways in which infection is detected and distinguished from other causes of similar signs, and the range of approaches used when treatment is considered appropriate.
Why this matters now
Lyme disease is transmitted through the bite of infected Ixodes ticks. In the UK and Europe the principal vector is Ixodes ricinus, the sheep or castor bean tick, while in North America the principal vectors are the black-legged tick (also called the deer tick, Ixodes scapularis) in the northeastern, mid-Atlantic, and north-central United States, and the western black-legged tick (Ixodes pacificus) along the Pacific coast, with the geographic distribution of the disease closely following the range of these tick species. In the UK, Ixodes ricinus is most active in spring and early summer, with a second period of activity in autumn; in hotter areas activity can almost stop during summer, and the exact pattern varies with climate and habitat. European guidance states that a tick must be attached for at least 16 to 24 hours before Borrelia is passed on, and the North American consensus statement puts transmission usually after 36 to 48 hours of attachment. Early tick removal therefore reduces the risk, but these figures are not a guaranteed safe limit for any one bite. Dogs in endemic areas may encounter infected ticks frequently, and seroconversion (the development of antibodies indicating exposure) is common in these regions, though only a minority of seropositive dogs develop clinical disease. The delay between tick bite and the appearance of clinical signs, which can span weeks to months, means that by the time symptoms emerge, the original tick exposure may be long forgotten.
When clinical Lyme disease does develop, it most commonly manifests as an acute or episodic polyarthritis (inflammation affecting multiple joints), producing lameness that may shift between limbs and may wax and wane over time. This joint involvement can appear suddenly, sometimes with significant discomfort, and may resolve spontaneously before recurring. A subset of affected dogs may develop Lyme nephritis, a serious and potentially life-threatening form of immune-mediated kidney disease characterised by protein loss through the kidneys. This renal form can progress rapidly to kidney failure. The relationship between the duration of infection and the likelihood of developing serious complications is not straightforward, and some dogs may develop nephritis without prior obvious joint disease.
Signals & patterns
Early signals
Shifting-leg lameness
One of the more characteristic presentations of Lyme disease is lameness that appears to move between different legs over time. A dog may be lame on one leg, appear to improve, then develop lameness on a different leg. This shifting pattern reflects the migratory nature of the joint inflammation.
Joint swelling and warmth
Affected joints may feel swollen, warm, and tender to the touch, and the swelling may be subtle or more obvious depending on the degree of inflammation.
General malaise and reluctance to move
Dogs with early Lyme disease may show a general reduction in activity, stiffness on rising, and reluctance to engage in normal activities such as walks or play. This can be accompanied by a mildly elevated temperature and a subdued demeanour.
Intermittent appetite reduction
Mild, intermittent decreases in appetite may accompany episodes of joint inflammation, reflecting the general malaise associated with the systemic inflammatory response rather than a specific gastrointestinal effect.
Later signals
Persistent or worsening lameness
While early Lyme arthritis may be episodic and self-resolving, some dogs develop more persistent joint inflammation that becomes less responsive to time alone. The lameness may become more consistently present and may affect the dog's willingness to exercise and overall quality of life.
Signs of kidney involvement
Lyme nephritis may manifest through increased thirst and urination, reduced appetite, weight loss, lethargy, vomiting, and peripheral oedema (swelling of the limbs or face). These signs may develop relatively suddenly and can progress rapidly. Lyme nephritis is the most serious potential complication: in the 49-dog series that first described it, the disease was uniformly fatal, although milder forms may exist.
Progressive lethargy and weight loss
Dogs that develop systemic complications may show progressive decline in energy levels and body condition, reflecting the cumulative effects of chronic inflammation, discomfort, and in cases of nephritis, protein loss and metabolic disruption.
Click to read about the biological mechanisms
How this is usually investigated
Investigating Lyme disease in dogs involves a combination of serological testing, clinical assessment, and exclusion of other conditions that can produce similar signs. The interpretation of test results requires careful consideration of the dog's geographic location, exposure history, and clinical picture, as positive serology does not always equate to clinical disease.
Point-of-care antibody screening
Quantitative C6 antibody testing
Urinalysis and urine protein assessment
Joint fluid analysis
Blood tests
Options & trade-offs
Management of clinical Lyme disease centres on antibiotic therapy to address the bacterial infection, alongside supportive care for any complications. The approach may vary depending on whether the dog has uncomplicated Lyme arthritis or has developed the more serious renal manifestation.
Antibiotic therapy
Doxycycline is the most commonly used antibiotic for treating Lyme disease in dogs, typically administered for a course of four weeks. UK-authorised doxycycline tablets for dogs do not list Lyme disease among their uses, so it is prescribed under the veterinary medicines cascade. The antibiotic targets the Borrelia spirochaetes and most dogs with uncomplicated Lyme arthritis show significant improvement within 1 to 3 days of starting treatment.
Trade-offs: While most dogs respond well to antibiotic therapy, some may experience recurrence of clinical signs after completing treatment. Improvement is expected within 1 to 3 days, and lack of response may prompt reconsideration of the diagnosis. Improvement does not prove Lyme disease, because doxycycline also treats co-infections such as anaplasmosis and has anti-inflammatory effects of its own. Gastrointestinal side effects from doxycycline occur in some dogs and can be managed with dietary adjustments.
Anti-inflammatory and analgesic support
Pain management during active episodes of Lyme arthritis may include anti-inflammatory medications to reduce joint swelling and discomfort while the antibiotic therapy takes effect.
Trade-offs: Anti-inflammatory medications provide symptomatic relief but do not address the underlying infection. Their use alongside antibiotics can help maintain comfort and mobility during the acute phase. As with any anti-inflammatory therapy, potential gastrointestinal and renal effects require consideration, particularly in dogs being monitored for Lyme nephritis.
Renal-directed therapy for Lyme nephritis
Dogs that develop Lyme nephritis require a more intensive management approach that may include immunosuppressive therapy to address the immune-mediated component, medications to reduce proteinuria, dietary modification, and supportive care for declining renal function.
Trade-offs: Lyme nephritis is far more serious than Lyme arthritis, and it is described as the only fatal form of Lyme disease in dogs. Early detection through routine urinalysis monitoring of Lyme-positive dogs may allow earlier intervention. The decision to pursue aggressive treatment involves considering the severity of renal compromise, response to initial therapy, and quality of life.
Prevention strategies
Tick prevention through topical or oral tick-control products represents the primary strategy for reducing Lyme disease risk. Vaccination against three Borrelia species found in Europe is available and may be considered for dogs in endemic areas, though the decision involves weighing individual risk factors.
Trade-offs: No tick prevention method is 100% effective, and regular tick checks after outdoor activity remain valuable even in dogs on preventive products. Lyme vaccination protocols vary among veterinary professionals, with some advocating vaccination in high-risk areas and others relying primarily on tick prevention. The cost-benefit analysis depends on geographic risk, lifestyle factors, and individual health considerations.
Common misconceptions
"A positive Lyme test means the dog has Lyme disease"
Antibody tests for Lyme disease detect exposure to the Borrelia organism, not necessarily active clinical disease. In endemic areas, a substantial proportion of dogs test positive for Lyme antibodies without ever developing clinical signs. A positive test indicates that the dog's immune system has encountered the bacterium, but clinical disease only develops in a minority of exposed dogs. Positive serology in the absence of clinical signs is generally not considered an indication for antibiotic treatment, though it may prompt urinalysis screening for subclinical proteinuria.
"Lyme disease always causes a bull's-eye rash in dogs as it does in humans"
The characteristic erythema migrans rash (the expanding circular rash seen at the tick bite site in human Lyme disease) is rare in dogs. This is partly because the skin reaction is difficult to see under fur, but also because the cutaneous response to Borrelia infection may differ between species. The absence of a visible skin lesion does not exclude Lyme disease in dogs.
"Lyme disease in dogs is a chronic, lifelong condition"
Most dogs with uncomplicated Lyme arthritis respond well to antibiotic therapy, often showing improvement within days of starting treatment. While some dogs may experience recurrence, the acute joint inflammation typically resolves with appropriate treatment. Lyme nephritis, however, is a separate and serious complication: it is uncommon, with protein loss in the urine found in fewer than about 2% of seropositive dogs, and can progress rapidly to kidney failure. The characterisation of Lyme disease as inevitably chronic does not reflect the experience of the majority of clinically affected dogs.
Related conditions
Lyme Nephritis
Lyme nephritis is an uncommon but serious immune-mediated kidney complication associated with Borrelia infection, and awareness of it shapes monitoring after a Lyme diagnosis.
Anaplasmosis
Anaplasmosis is transmitted by the same Ixodes ticks that carry Borrelia, so co-infection occurs, and the two produce overlapping signs of fever, lethargy, and shifting lameness.
Ehrlichiosis
Ehrlichiosis is another tick-borne bacterial infection producing fever and lethargy, and it features alongside Lyme disease in the differential picture for dogs with tick exposure.
Babesiosis
Babesiosis is a tick-transmitted parasitic infection considered alongside Lyme disease in dogs with tick exposure and non-specific illness, particularly where travel or an unusual tick population is involved.
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Immune-Mediated Polyarthritis
Immune-mediated polyarthritis is a key differential for the shifting-leg lameness and joint pain seen in Lyme disease, and distinguishing the two changes the treatment approach considerably.
Understanding Lyme disease involves recognising the distinction between exposure and clinical disease, appreciating the role of geographic risk and tick ecology, and being aware of the spectrum of possible manifestations from self-resolving arthritis to serious renal disease. For dogs living in or travelling to endemic areas, awareness of tick prevention strategies, familiarity with the early signs of Lyme arthritis, and understanding the value of routine screening and urinalysis monitoring all contribute to informed management of this tick-borne infection.
Last reviewed: 10 October 2026 · Dr Alastair Greenway MRCVS