Lyme Disease in Dogs
Lyme disease is a clinical disorder caused by a microscopic organism, the spirochete (Borrelia burgdorferi), and is spread by ticks. There are other species of Borrelia, but B. burgdorferi seems to be the only spiral-shaped bacteria that infects small mammals, especially mice. Ticks then feed on the mammals and carry the bacteria to their victims.
The tick vectors for B. burgdorferi are hard-shelled Ixodes ticks. In the US, these are primarily I scapularis (the deer tick) in the northeast and Midwest and I pacificus (the western black-legged tick) on the Pacific coast. The deer tick is the most common tick to spread the disease, although other ticks can pass it along as well.
The life cycle of the tick is important to understanding the transmission of lyme disease. The stages of maturation of a tick include:
- Larvae (larval ticks only have 6 legs)
- Nymph (nymph ticks have 8 legs)
The tick can become infected with the bacteria at any point when they are larvae or nymph, if they feed on an infected host. Ticks themselves are considered reservoir hosts and have to be feeding on a mammal for over 24 hours for the bacteria to spread. During a blood meal, stable transmission takes over 53 hours into feeding to spread. The likelihood of transmission of the bacteria if the tick is attached for under 24 hours is very low.
The disease is named after the initial discovery in human beings that occurred in 1975 in Lyme, Connecticut. Lyme disease can affect different organs and body systems and is most common in canine species.There appears to be no breed or sex predisposition. Outside, hunting and working dogs are more likely to be exposed to ticks than dogs kept indoors. Female dogs that are infected before pregnancy can transmit the spirochetes to the unborn puppies.
Human data from the Centers of Disease Control reports 30,000 new cases of lyme disease yearly, but this data may under represent the actual number of cases in the United States. The prevalence in veterinary species is less well known, but the Companion Animal Parasite Council notes the prevalence of lyme disease in dog populations to be 1.4% on the west coast and as high as 13.3% on the east coast. The prevalence is low in nonendemic areas like the south.
The most consistent clinical sign in dogs is lameness with swollen joints that are warm to the touch. Lyme disease can also cause cardiac (heart), renal (kidney), and neurological symptoms.
Common clinical signs include:
- Recurrent lameness in a joint (with complete recovery)
- Shifting leg lameness
- Reluctance to move (pain)
- Swelling in one or more joints
Lyme nephritis is a severe, but rare, disease that dogs can develop from B. burgdorferi and is thought to be secondary to immune complex accumulation in the kidneys.
Clinical signs associated with lyme nephritis include:
- Weight loss
- Muscle wasting
- Poor appetite
- Bad breath/halitosis
Diagnosis of Lyme Disease in Dogs
Lyme disease is usually diagnosed by the presence of clinical symptoms and by blood testing. Certain diagnostic tests must be performed to confirm the diagnosis of Lyme disease and exclude other diseases that may have similar symptoms.
A complete medical history and physical examination should be obtained by your veterinarian. Special attention should be paid to joints, lameness evaluation, and auscultation (stethoscope examination) of the heart. Diagnosis is based on physical exam, history, clinical signs, rule-outs, positive serology, and response to antibiotics.
- The first step in diagnosis is a snap ELISA test, which looks for antibodies and is readily available with rapid results. If a positive test is noted on ELISA, then further confirmatory testing should be pursued. Vaccinated dogs can test positive on ELISA snap. The ELISA also tests for 2 other common tick-borne diseases, ehrlichia and anaplasmosis, which present symptoms similar to lyme disease.
- Additional confirmatory testing can be done with Western blot and line immunoassay (LIA). Western blot is useful to distinguish between antibody levels generated due to infection vs. those due to vaccination.
- Peptide-based testing that is specific for infection-derived antibodies is available, and is commonly referred to as the C6 test. This indicates exposure to the antigen, but doesn’t mean clinical disease is present.
- Joint fluid analysis may be done in arthritic or lame joints. This test can also help determine the cause of the lameness and rule out other infections.
- Radiographs (X-rays) may be performed on swollen or lame joints. Swelling in the joint (effusion) is a common finding with Lyme disease, but the radiographs should otherwise be normal.
- Additional full PCR testing for tick-borne diseases may be necessary.
Your veterinarian may recommend additional diagnostic tests to exclude or diagnose other conditions or to better understand the impact of Lyme disease on your pet. These tests ensure optimal medical care and are selected on a case-by-case basis.
Tests may include:
- Complete blood count (CBC) may be needed to evaluate your dog for other problems such as infections, inflammations, or platelet-related diseases.
- Serum biochemistry tests that can evaluate liver, kidneys, and electrolytes.
- Urinalysis may be recommended to evaluate the kidneys and bladder.
- Coagulation (blood-clotting) profile may be completed to evaluate for bleeding abnormalities.
Treatment of Lyme Disease in Dogs
Treatment of Lyme disease must be based on the severity of the condition and other individualized factors that must be analyzed by your veterinarian. If your dog has only a positive titer and no clinical signs, no treatment may be recommended. In this situation, regular follow-up visits to your veterinarian are important to ensure the condition does not progress. If the Lyme disease affects other organ systems, such as the heart or kidneys, additional treatment is necessary.
This may include prescription antibiotics, which usually provide improvement in clinical signs in 24 to 48 hours. This is thought to be due to a decrease in bacterial load, and not elimination of the bacteria, since the antibodies stay persistent for long periods. Improvement is usually noted within three days of initiation of antibiotic therapy, or for 14 to 21 days (recommendations vary from two to four weeks) with drugs like tetracycline (often avoided in growing dogs), doxycycline, minocycline, cephalexin, amoxicillin, or ampicillin. An injectable antibiotic known as Convenia can also be used. Doxycycline is preferred over other antibiotics.
Dogs should be monitored after treatment for resolution of clinical signs, as well as periodically for protein in urine (proteinuria).
Most cases of lyme disease respond well with a course of antibiotics. In more severe cases or in cases of lyme nephritis, treatment is more intense and clinical outcome is poor, even fatal. Golden and Labrador Retrievers tend to be overrepresented in breeds that develop lyme nephritis. In one study of lyme nephritis, 49/49 dogs were euthanized 1-8 weeks after diagnosis. Dogs with lyme nephritis often need treatment with blood pressure medications, platelet inhibitors, gastroprotectants, anti-nausea medications, and fluid therapy.
Other medical problems can lead to symptoms similar to those encountered in Lyme disease. It is important to exclude these conditions before establishing a definite diagnosis.
- Degenerative joint disease
- Drug reaction (sulfadiazine reaction in Doberman Pinschers)
- Ehrlichiosis, which is also a tick-borne disease, is caused by parasite infection and diagnosed with Ehrlichia serology and platelet counts.
- Immune-mediated polyarthritis
- Musculoskeletal injury or trauma
- Osteochondritis dissecans (OCD), which is an inflammation of the bone and cartilage.
- Osteopathy (any bone disease)
- Panosteitis (inflammation of every part of a bone)
- Rheumatoid arthritis
- Rocky Mountain spotted fever
- Septic arthritis
- Systemic lupus erythematosus
Follow-up Care for Dogs with Lyme Disease
Optimal treatment for your dog requires a combination of home and professional veterinary care.
Follow-up can be critical and may include the following:
- Administer any veterinarian-prescribed medications. Observe your dog’s general activity level, appetite, and interest.
- Schedule regular veterinary visits to monitor your pet’s condition.
- Blood samples should be checked to monitor the Lyme disease titer.
- Of course, the precise follow-up depends on the severity of your dog’s disease, response to therapy, and your veterinarian’s recommendations.
- Be certain to contact your veterinarian if you are experiencing any problems treating your pet.
The best prevention from lyme disease is minimizing tick exposure and tick attachment to your dog. Year-round monthly tick preventative is recommended, especially in endemic areas. This can be topical or oral preventatives. There are also tick collars that can be used, but need to consistently be worn at all times to be preventative. After being exposed to an area that might have ticks, checking for ticks is very important. They tend to attach between the toes, around the face, muzzle and ears, but they can be anywhere.
It is important to look for ticks on your pets and yourself after being outside. Ticks can be carried into the home with pets and then attach to humans to transmit disease.
If you live in an area at high risk for Lyme disease, discuss vaccination with your veterinarian. For more information on the risk of Lyme disease in your state or county, go to capcvet.org. This website will let you filter infection rates of Lyme disease in dogs in your state and county by disease.