Lyme disease in dogs: symptoms and what a positive test means

Reading time: about 8 min

With some diseases, it isn’t easy to say, “Don’t worry, most dogs do well.” If you have seen a dog seriously affected by one, that experience stays with you. Irene’s Labrador, Pekwa, suffered severe Lyme disease at about six years of age. It took months to reach the diagnosis, and the distress wasn’t only about ticks: for a long time, nobody knew why the dog was unwell. I understand why reliable tick prevention feels especially important after an experience like that.

At the same time, I’ve always wanted to understand exactly which risk we are reducing and which risks may accompany the preventive product itself. Years ago, Dr Karen Becker’s discussions of Lyme disease made me ask how many infected dogs actually become ill. Today, I would frame the question more precisely: what does exposure to Borrelia mean, what does a positive test tell us, when is clinical disease likely, and how can we choose appropriate prevention without dismissing either side of the risk equation?

What is Lyme disease and how do dogs get it?

Lyme borreliosis is caused by bacteria belonging to the Borrelia burgdorferi sensu lato complex, transmitted by infected ticks. In Europe, we need to consider local Ixodes species, including Ixodes ricinus, which also occurs in Estonia. American sources often focus on the black-legged tick Ixodes scapularis. That distinction matters: figures and prevention practices from one part of the United States cannot automatically be applied to a dog in Estonia.

Infection requires exposure to a tick carrying the organism. Not every tick carries Borrelia, not every bite leads to infection, and not every infected dog develops clinical illness. These are three different stages. Removing an attached tick promptly makes sense because the risk of transmission rises with attachment time. However, “36 hours” is not a universally safe cut-off. Tick species, bacterial factors, previous feeding and other circumstances are not things an owner can assess reliably at home.

A dog does not transmit Lyme disease to a person simply through petting, sleeping in the same bed or having a positive blood test. For people and dogs alike, the central source of infection is an infected tick. Tick control can therefore help reduce risks in the household, although the dog itself is not the usual direct source of human infection.

Do most dogs exposed to Borrelia remain healthy?

Many have no symptoms. The 2018 ACVIM consensus notes that most dogs testing seropositive for Borrelia do not show clinical signs of disease. This is an important reason to distinguish detection of antibodies from active illness. But I wouldn’t put it as “exactly 95% of all dogs bitten by a tick are protected, and 5% fall ill”. That combines exposure to an infected tick, infection, antibody response and clinical illness, and ignores regional differences in the data.

Some dogs encounter the organism without visible disease; others develop fever and lameness; in rare cases, more serious kidney disease has been associated with infection. We cannot use a population percentage to predict which group an individual dog will enter. Pekwa’s experience does not cancel out the fact that many dogs never become ill. Equally, an average statistic does not make Pekwa’s suffering any less real.

Lyme disease symptoms in dogs: what should make you pay attention?

One of my first warning signs is a dog behaving differently from usual after spending time outdoors. Perhaps the dog becomes subdued, avoids exercise, eats less or starts limping. That does not automatically mean Lyme disease, but it is a reason to observe the situation more closely.

Possible signs of canine Lyme disease include:

• Lameness that may come and go, recur, or affect different legs.
• Joint pain or inflammation, sometimes with swelling or warmth around a joint.
• Stiff or painful movement, especially after resting or when starting to walk.
• Reluctance to walk, exercise, climb stairs or play as usual.
• Fever and general malaise.
• Reduced appetite or refusal to eat.
• Tiredness, lethargy and more sleep than usual.
• Behavioural changes, such as withdrawal or reduced interest in surroundings.
• Enlarged lymph nodes, which may sometimes be visible or palpable.

Not all of these signs need to occur together. One dog may primarily show lameness, another fever and a generally poor condition. None is unique to Lyme disease. Injuries, other tick-borne infections and several joint conditions can produce similar problems.

How soon after a tick bite do symptoms appear?

There is an important nuance here. If a dog becomes lethargic or starts limping only a couple of days after a forest walk, it is worth taking seriously, but that rapid onset is not typical of canine Lyme disease.

Illness linked to Borrelia may appear weeks or even months after infection. An owner may no longer remember any tick exposure. On the other hand, some other tick-borne infections can cause symptoms much sooner.

Redness at the bite site does not automatically indicate Lyme disease either. The characteristic expanding ring-shaped rash described in people is not an equally typical or reliable diagnostic sign in dogs.

Can Lyme disease affect a dog’s kidneys?

Although joint problems and general illness are better-known manifestations, a serious kidney disorder referred to as Lyme nephritis has also been described in dogs.

Possible signs of kidney involvement include loss of appetite, vomiting, marked lethargy, changes in drinking or urination and sometimes swelling. A dog showing these signs needs prompt veterinary assessment.

It is essential to distinguish two facts: a dog with positive Borrelia antibodies can have kidney disease, but the positive test alone does not prove that Borrelia caused the kidney damage. Other possible causes must be investigated as well.

Does canine Lyme disease have three stages?

Human Lyme disease is often described in terms of early localised, early disseminated and late disease. It is not justified to automatically apply the same three-stage model with fixed percentages to dogs.

Many dogs exposed to Borrelia never become visibly ill. Some develop joint problems and general symptoms, while serious forms have been described less commonly. There is no reliable universal percentage chart predicting how many tick bites in dogs lead to a first, second or third disease stage.

For me, noticing changes in the dog’s wellbeing and behaviour matters more than trying to assign it to a stage, particularly if tick exposure is known. Unexplained lameness, fever or marked lethargy warrant veterinary advice. Vomiting, severe weakness, swelling or changes in urination mean that assessment should not be delayed.

What does a positive Lyme disease test mean?

4Dx-type screening tests and other antibody tests may indicate prior exposure to the organism. A positive result does not, by itself, prove that Lyme disease is causing the dog’s current lameness. Antibodies can persist long after exposure. Conversely, an early negative test cannot always exclude a very recent infection, because antibodies take time to develop.

A diagnosis should not rest on one positive line on a test strip. The veterinarian must consider medical history, examination findings, symptoms, likely tick exposure and, when indicated, additional blood and urine tests. Testing for other tick-borne diseases may also be appropriate. When symptoms and laboratory findings do not fit together, the answer is not to forget the whole dog and focus only on a test result.

One of the most important “but why?” questions for me is this: if antibodies are positive but the dog is entirely well, what exactly would we achieve with antibiotics? The ACVIM working group did not agree unanimously, but most members did not recommend automatic antibiotic treatment for every asymptomatic seropositive dog without proteinuria. There must be a reasonable expectation of clinical benefit.

How is a dog with clinical Lyme disease treated?

Antibiotic treatment is a standard part of care when clinical canine Lyme disease is suspected. ACVIM describes doxycycline as one preferred drug and discusses approximately four weeks of treatment for classical Lyme arthritis. The veterinarian chooses the exact drug, dose and duration based on the dog’s condition, concurrent illnesses and possible alternative diagnoses. If the dog does not improve as expected, the diagnosis should be reconsidered rather than merely extending antibiotics indefinitely.

You may find online discussion of human studies on a single preventive dose of doxycycline after a tick bite. This must not be turned into a home instruction for dogs. Giving one tablet after every tick bite is not an established evidence-based standard of canine prevention. Antibiotics are best used when there is a reasonable likelihood of clinical benefit.

Chemical or natural tick prevention?

I don’t think it is right to present registered tick-control products as entirely risk-free. As with any active substance, the safety information for the specific preparation, the dog’s age and health, possible interactions, adverse effects and directions for use all matter. Some dogs tolerate one formulation better than another. This is a sensible subject for discussion with a veterinarian, not a reason to treat all products as interchangeable.

The opposite extreme would be to assume that good food, a strong immune system or a naturally scented spray offers the same protection as an effective, tested tick-control product. Integrative veterinarians often emphasise nutrition, general health, skin and coat care, and regular tick checks and removal. These can be valuable parts of overall care, but they do not prove that a dog cannot acquire Borrelia. Possible repellent effects of some plant products are not the same as demonstrated reduction of disease risk.

Lyme vaccination is used in some countries, particularly in North America. Whether it is appropriate or available depends on local circumstances, authorised products and the dog’s exposure risk. The 2018 ACVIM group did not reach consensus on vaccination. Karen Becker has expressed concerns about it, but that does not justify claiming that every vaccine causes autoimmune disease. Vaccination also does not stop ticks attaching to a dog and cannot replace tick control.

For my own dogs, I’ve wanted to consider both sides: reducing exposure to ticks without choosing a product simply because it is the easiest option. It is possible to make an informed decision. The key is understanding the risk that remains when effective tick control is not used.

After outdoor walks, check the dog carefully, especially around the ears, under the collar and harness, in the armpits, between the toes and under the tail. Remove attached ticks as soon as possible using a suitable tool, close to the skin and gently. There is no need to oil a tick or attempt to suffocate it with chemicals. If the dog becomes unwell, mention possible tick exposure to the veterinarian, even if you don’t remember a particular bite.

Can nutrition and inflammation affect the course of illness?

Overall health can influence immune responses and recovery, and here the integrative perspective has a reasonable place. A balanced diet, adequate energy and nutrients, adjusted activity and attention to other health problems can help support a sick dog. The biological mechanisms by which omega-3 fatty acids influence inflammatory mediators have been studied, but this does not mean that fish oil treats borreliosis or that fatty acid ratios predict an individual dog’s infection.

Nor can we reliably claim that ticks choose dogs “full of toxins” or that liver cleanses, heavy-metal detox courses or supplements prevent Lyme disease. When a dog is ill, finding the actual cause and supporting recovery according to its needs are more useful. Supportive care cannot replace necessary treatment for bacterial disease. At the same time, I wouldn’t mock integrative veterinarians for exploring whether a healthier animal may be less attractive to parasites. That remains a separate hypothesis, not proven protection.

FendaF’s practical check after a tick encounter

Remove the tick promptly and note the date if useful. Over the following weeks, monitor the dog’s usual movement, appetite, temperature, energy and urination. Do not give antibiotics preventively on your own. Contact a veterinarian if fever, lameness, marked lethargy, vomiting or urinary changes occur. If the Lyme test is positive, ask whether it indicates exposure alone or whether signs of clinical illness are present, and whether urine testing is appropriate.

In summary

Pekwa’s story reminds me why Lyme disease should never be dismissed lightly. At the same time, not every tick bite results in illness and not every positive blood test means a disease that needs treatment. Sensible prevention, diagnosis and treatment must fit between those two realities. The question isn’t simply “am I more afraid of ticks or medication?” but “what risk does each action actually reduce, and what do we know about it?”

Sources

• Littman et al. (2018). ACVIM consensus update on Lyme borreliosis in dogs and cats. Journal of Veterinary Internal Medicine.
• ESCCAP. Control of Vector-Borne Diseases in Dogs and Cats, Lyme borreliosis.
• ESCCAP. Control of Ectoparasites in Dogs and Cats.
• FendaF. How safe are chemical tick treatments for dogs? Related reading.

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