Testing for Lyme Disease in Dogs

By Kristiina Ruotsalo, DVM, DVSc, Dip ACVP & Margo S. Tant, BSc, DVM, DVSc

Diagnosis

December 3, 2008

What is Lyme disease? How does my dog get infected?

lyme_disease_-_testing-1Lyme disease is an infectious disease caused by bacteria called Borrelia. The bacteria are most commonly carried by the deer tick, also called a black-legged tick. Infection occurs when a dog is bitten by an infected tick, although the tick must remain attached to the dog for at least two days before it is able to pass the infection onto the dog. The tick itself becomes infected by feeding on infected mice, birds, deer, and other animals.

Where is Lyme disease found?  

In the United States, Lyme disease has been reported in every state, but over 95% of cases are from the Northeastern, Mid-Atlantic, and upper Midwestern states (New England states to Virginia, Wisconsin and Minnesota), with a small number of cases reported along the West Coast, especially Northern California. In Canada, Lyme-positive dogs are found mostly in southern Ontario and southern Manitoba, with a small number of cases in southern Quebec and the Maritime provinces.

Does being outdoors put my dog at greater risk for catching Lyme disease?

Yes. Dogs that spend a lot of time outdoors are more likely to be infected, especially if they visit wooded areas where deer ticks are abundant. The highest risk areas are deciduous (hardwood) forests that have moist sandy or loamy soil and thick vegetation. This includes forested woodlands in the country as well as wooded areas in city parks.

"The risk of infection is greatest in the warmer months of the year."

The risk of infection is greatest in the warmer months of the year from spring through autumn when ticks are most active.

What should I do if I find a tick on my dog?

lyme_disease_-_testing-2The tick should be removed promptly but carefully so that none of the tick's mouthparts are left in the dog's skin. If you are not sure how to do this, then take your dog to a veterinarian to have the tick removed safely. The tick can be sent to the laboratory to see if it is a deer tick, and if it is, then it can also be tested to see if it is infected with Lyme disease.

If the tick is an infected deer tick, then the dog should be monitored signs of infection and your veterinarian may recommend antibiotic treatment. Your veterinarian can also advise you about how to protect your dog against further tick bites using tick control products.

Can infection be spread directly from one dog to another dog or from my dog to my family?

Direct spread of Lyme disease from one dog to another dog has not been reported, even when infected and uninfected dogs have lived together for long periods.

Spread of Lyme disease from dogs to people has not been reported either, but people are equally at risk for Lyme disease if they are bitten by an infected tick.

What are the signs of Lyme disease?

The most common sign is lameness, but a small percentage of dogs develop severe life-threatening kidney disease. Younger dogs are more likely to show clear signs of illness than mature dogs. In some dogs, the signs may be vague and may not appear for several months after a bite from an infected tick. Many dogs do not show any signs of illness at all.

Lameness: Severely infected dogs may show sudden lameness involving one or more joints. Affected joints are swollen and painful, and the lameness may shift from one leg to another. Joint fluid collected from sore joints shows large numbers of inflammatory cells. Other signs include fever, lethargy, poor appetite, and sometimes enlarged lymph nodes. Routine blood tests from infected dogs are not helpful in diagnosing the disease.

"Long-term infection may lead to progressive and permanent damage to the joints."

For many dogs, the lameness is mild and passes quickly, so pets may not get proper treatment. Although the lameness resolves, the dog remains infected and may continue to experience episodes of lameness that shifts from leg to leg. This long-term infection can lead to progressive and permanent damage to the joints.

Kidney failure: A less common but more serious consequence of Lyme disease is sudden kidney failure accompanied by protein loss in the urine. In some dogs, kidney involvement appears at the same time as lameness, but in other dogs it appears 3-6 weeks after an episode of lameness. Dogs with kidney involvement show signs of lethargy, poor appetite, vomiting, and weight loss. Routine laboratory tests on these dogs show abnormalities typical of kidney failure, including protein loss in the urine.

How is Lyme disease diagnosed?

The traditional blood tests for diagnosing Lyme disease have replaced by two new tests called the C6 Test and Quant C6 test.
The C6 test is a preliminary blood test that detects antibodies against a very specific protein called “C6”. This protein is unique to the Borrelia bacteria, and the presence of antibodies to C6 suggests active Lyme infection. The C6 antibodies can be detected three to five weeks after a dog is bitten by an infected tick, and may be found in the blood stream even before the dog shows signs of illness. The C6 test is offered as part of a package of tests that looks for other tick-borne diseases. The test can be done by your veterinarian in-clinic or the blood sample can be sent to the laboratory for testing.

If the C6 Test is positive, what is the next step?

A positive C6 Test means antibodies to C6 were found. The next step is to do a Quant C6 test, which determines if the levels of antibody are high enough to justify treatment. If the value of the Quant C6 is higher than 30 IU/mL and signs of illness are present then antibiotic treatment should be considered. If the Quant C6 is less than 30 IU/mL and there are no signs of illness, then treatment may not be necessary.

In addition to doing the Quant C6 test, your veterinarian may want to take samples of blood and urine to assess kidney function and to look for protein in the urine. A positive test for protein in the urine could signal serious underlying kidney disease.

To treat or not to treat?

The decision to treat Lyme disease is somewhat controversial since many infected dogs show no signs of illness.  
Factors that would support treatment include:

•    a moderate to high value of Quant C6
•    signs of illness compatible with Lyme disease at the time of testing
•    a history of illness compatible with Lyme disease within the past year
•    the presence of abnormal levels of protein in the urine.

What is the treatment for Lyme disease?

Several different antibiotics are listed for use in treating Lyme disease, but doxycycline and amoxicillin are two that are commonly used. Most dogs show improvement within 24 to 48 hours of starting treatment. The duration of antibiotic treatment can vary, but most dogs are treated for 30 days.

Dogs that develop kidney failure and/or urinary protein loss will also require additional treatment for the kidney problem. The amount of treatment needed depends on the severity of illness and may include hospitalization with intravenous fluid therapy, antibiotics, and other medications.

How can I tell if treatment is working?

A dog's response to therapy can be assessed by repeating the Quant C6 test six months after treatment is complete. Dogs that start with a moderate to high Quant C6 value typically show a 50% reduction or more in the Quant C6 at six months, indicating that treatment has been successful. Dogs that have a lower initial Quant C6 value may not show such dramatic reductions in the Quant C6 at six months, although the value should still be lower than the starting point if treatment has been successful. A persistently high Quant C6 suggests treatment may not have been complete or that the dog became re-infected after treatment was stopped.

Is treatment 100% effective?

Scientists are divided on this topic. Some studies suggest that that even long-term antibiotics may not completely clear infection; dogs may get sick again at some point after antibiotic treatment is stopped. Other studies suggest that complete clearance of infection is possible with antibiotic treatment. Further research is required to answer this question.

Is there a vaccine against Lyme disease?

There are several vaccines available. Not all dogs need to be vaccinated, and the decision to vaccinate would be determined by factors such as the level of Lyme disease in your community, the amount of time your dog spends outside, and the potential for side effects from the vaccine itself. Vaccination does not interfere with the C6 or Quant C6 tests.

How can I prevent Lyme disease in my dog?

The best way to prevent Lyme disease is to have a good tick control program for your dog. The use of commercial products to prevent tick bites can greatly reduce the risk of Lyme disease. There are a number of effective products available, and your veterinarian can advise you on which one is best for your pet. In addition, if your dog spends a lot of time outdoors, always carefully inspect your dog's skin and hair coat to look for ticks after coming inside; prompt removal of ticks reduces the chances that Lyme disease will be transmitted to your dog. Annual C6 testing is also a good idea for dogs that live in high-risk areas, since early detection and proper treatment of Lyme disease will prevent any long-term damage.

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