Is Diarrhea a Symptom of Lyme Disease in Dogs? | Tick Talk

Picture this: your dog has been limping off and on for a few days, seems tired, and runs a low fever. You Google the symptoms and wonder if Lyme disease could be the cause. Then you notice a loose stool and ask yourself — is diarrhea a symptom of Lyme disease in dogs? It’s a fair question, but the answer is more about what Lyme typically looks like versus what it doesn’t.

The honest answer is that diarrhea is not listed among the classic Lyme disease signs by any major veterinary authority. The most common symptoms center on joints, energy levels, and appetite. Diarrhea has other, far more likely causes in dogs — and even when Lyme is present, gastrointestinal upset is usually not the reason.

What Lyme Disease Actually Looks Like in Dogs

Lyme disease in dogs is caused by the bacterium Borrelia burgdorferi, transmitted through the bite of an infected black-legged tick. Most dogs exposed to the bacteria never become ill — clinical signs, when they appear, surface two to five months after the tick bite.

According to Cornell University’s College of Veterinary Medicine, the most common symptoms are lameness, swollen lymph nodes, joint swelling, fever, and lethargy. The American Veterinary Medical Association (AVMA) adds loss of appetite and lameness that comes and goes.

The Gastrointestinal Piece

Neither source lists diarrhea as a primary sign. Gastrointestinal symptoms are not the hallmark of Lyme disease in dogs, though they can occur if the infection progresses to a kidney complication called Lyme nephritis. That’s an advanced, serious condition — not the typical picture.

Why Lyme and Diarrhea Get Confused

Dog owners sometimes tie Lyme to diarrhea because other tick-borne illnesses present differently. Ehrlichiosis and tularemia, for example, list nausea, vomiting, and diarrhea among their direct symptoms. When a dog has a tick-borne illness with an upset stomach, the assumption can be Lyme — but it’s more likely one of these other infections.

• Ehrlichiosis: The Washington State Department of Health notes nausea, vomiting, and diarrhea as symptoms of ehrlichiosis, helping differentiate it from Lyme.
• Tularemia: The Alaska Department of Fish and Game lists coughing or diarrhea as possible signs of tularemia in pets, not Lyme.
• Anaplasmosis: Another tick-borne disease that sometimes includes vomiting and diarrhea, though joint pain and fever are more common.
• Babesiosis: Can cause fever, anemia, and dark urine — diarrhea is occasionally reported but is not a primary sign.

The takeaway: if your dog has diarrhea and you suspect a tick-borne disease, ask your vet about ehrlichiosis or anaplasmosis before assuming Lyme.

When Diarrhea Could Be Related to Lyme

There is one scenario where diarrhea may tie into Lyme disease: when the infection triggers severe kidney inflammation, known as Lyme nephritis. This rare complication can cause vomiting, lethargy, loss of appetite, and weight loss — and in some advanced cases, diarrhea may be reported.

However, Lyme nephritis is not a typical outcome. Most dogs with Lyme never develop it. The Ohio Department of Health recommends that dog owners watch for lameness, fever, and lethargy rather than gastrointestinal signs like diarrhea. Dogs are considered dead-end hosts for the bacteria, meaning they cannot transmit Lyme directly to humans, but they can still get sick — just not usually with diarrhea.

If your dog has diarrhea and also shows joint pain, fever, or lethargy, a veterinarian can run a C6 antibody test to check for Lyme. But standalone diarrhea is far more likely caused by something else.

Steps to Take if Your Dog Has Diarrhea

When a dog has loose stools, the odds overwhelmingly point to everyday causes, not Lyme disease. Follow these steps to identify the real culprit.

1. Check for dietary indiscretion: Did your dog eat something unusual — table scraps, garbage, or a new treat? Dietary indiscretion is the number one cause of diarrhea in dogs.
2. Consider intestinal parasites: Microscopic parasites like Giardia and roundworms can cause diarrhea. A fecal exam by your vet can rule them out.
3. Watch for other symptoms: If diarrhea is accompanied by vomiting, fever, lethargy, or joint pain, the list of possible causes widens and warrants a vet visit.
4. Rule out stress or diet change: A sudden switch in food, a boarding stay, or a stressful event can upset a dog’s gut for a day or two.
5. Evaluate for tick-borne illness only if other signs fit: If your dog has lameness, swollen lymph nodes, or a fever along with diarrhea — and lives in or has traveled to a tick-endemic area — ask your vet about tick-borne diseases.

Remember: a single episode of diarrhea in an otherwise alert, playful dog is usually not an emergency. But if it persists beyond 24 hours or includes blood, call your veterinarian.

Diagnosing and Treating Lyme Disease in Dogs

When Lyme disease is suspected, diagnosis relies on blood tests — not gastrointestinal symptoms. The Merck Veterinary Manual describes the C6 antibody test and quantitative C6 test as the standard tools. These measure antibodies to Borrelia burgdorferi, not responses from the gut.

Treatment typically involves a course of doxycycline, an antibiotic that resolves the infection in most dogs. Some dogs may have lingering joint pain and require additional support. Vaccination against Lyme is available in endemic areas and can reduce the risk of infection.

Cornell University’s Riney Canine Health Center offers a comprehensive overview of Lyme disease in dogs, covering prevention, diagnosis, and the realities of Lyme nephritis. It’s a trusted resource for understanding what to expect.

The Bottom Line

Diarrhea is not one of the typical signs of Lyme disease in dogs. The hallmark symptoms are lameness, fever, lethargy, joint swelling, and loss of appetite. Unless the infection has progressed to the rare kidney complication Lyme nephritis, diarrhea is almost certainly due to another cause — such as something your dog ate, a parasite, or a different tick-borne illness like ehrlichiosis.

If your dog has diarrhea along with joint pain or a fever, and you live in a tick-heavy region, a quick C6 test from your veterinarian can either confirm or rule out Lyme. For the vast majority of dogs, a case of loose stools means checking the kitchen trash, not the tick prevention schedule.