Lyme Disease

Laurie Anne Walden, DVM

Deer tick (Ixodes scapularis). Public domain image from CDC.

Lyme disease is the most common tick-borne disease in humans in the United States.[1] Dogs can be infected with the bacteria that cause Lyme disease but are much less likely than people to develop symptoms.
 
Transmission
Lyme disease is caused by infection with Borrelia burgdorferi bacteria, which are transmitted through tick bites. The tick responsible for infection in the eastern United States is Ixodes scapularis, the deer tick (also called the blacklegged tick). Deer ticks persist in the environment because they’re maintained in populations of deer and other wild animals. For this reason, Lyme disease is endemic—always present in the environment—in some parts of the country.
 
Deer ticks are smaller than American dog ticks and can be hard to see on animals with fur. The immature nymph stage, which can also transmit B burgdorferi, is tiny and even harder to spot.
 
Ticks live in woods, grassy areas, and underbrush. Ticks can’t jump or fly; they wait on the tip of a branch or grass blade until a person or animal brushes past, then they latch on. Adult deer ticks can be active when the weather is cool, so Lyme disease isn’t just a summertime risk.
 
Ticks transmit bacteria to the host animal while they’re taking a blood meal. It takes a day or two for B burgdorferi to pass from a tick into a host, so removing ticks within 24 hours reduces the risk of Lyme disease.
 
Humans and dogs don’t spread Lyme disease directly to each other, but dogs can bring ticks into the home. Infection in one host species also means that another host species living in the same environment is at risk. If a dog has a positive test for B burgdorferi, for example, that means the dog has been exposed to ticks carrying the bacteria, and people in the dog’s household are at risk for Lyme disease from the same ticks.
 
Symptoms
Most dogs (95%) infected with B burgdorferi don’t develop any symptoms. In dogs that become ill, symptoms start 2 to 5 months after infection and include fever, loss of appetite, and lameness that can shift from one leg to another. Some infected dogs develop kidney disease.
 
Cats can be infected with B burgdorferi, but whether they actually get sick from the infection is unknown.
 
Diagnosis
Many dogs are routinely tested for B burgdorferi antibodies at the same time as their annual heartworm test. Antibody tests show whether a dog has been exposed to the bacteria. The American College of Veterinary Internal Medicine recommends yearly antibody tests for all dogs living in or near areas where Lyme disease is endemic.[2] Dogs that test positive have further blood and urine tests to check kidney function and uncover other problems. A positive antibody test in a healthy dog also indicates a possible risk of Lyme disease for people living in the same environment.
 
Diagnosing Lyme disease in dogs with symptoms is not always straightforward. The same symptoms are caused by many different conditions. A positive antibody test means that at some point the dog was bitten by a tick carrying B burgdorferi, not necessarily that the infection is causing the current symptoms. A diagnosis is usually based on antibody test results (possibly more than 1 type of test), symptoms consistent with Lyme disease, lack of evidence of other causes of symptoms, and response to treatment.
 
Treatment
Dogs with symptoms of Lyme disease are treated with antibiotics. Dogs that develop kidney disease need additional treatment.
 
Prevention
Tick control is the best way to prevent Lyme disease. Many tick preventives are available for dogs; some are given by mouth and others are applied to the skin. Your veterinarian can suggest products best suited to your dog. Some products are available only by prescription.
 
The CDC website has lots of information about preventing tick bites in people and pets. See “Preventing Tick Bites” in the Lyme disease section of the CDC website: https://www.cdc.gov/lyme/prev/index.html
 
Vaccines for Lyme disease are available for dogs. Your veterinarian can advise you on whether you should consider having your dog vaccinated.
 
References
1. Lyme disease. Centers for Disease Control and Prevention. Accessed June 25, 2022. https://www.cdc.gov/lyme/index.html
2. Littman MP, Gerber B, Goldstein RE, Labato MA, Lappin MR, Moore GE. ACVIM consensus update on Lyme borreliosis in dogs and cats. J Vet Intern Med. 2018;32(3):887-903. doi:10.1111/jvim.15085
 
Ixodes scapularis image source: CDC

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