A Tick-Borne Illness in Dogs
“Many dogs that are bitten by an infected tick and become infected with
Borrelia burgdorferi bacteria do not develop any symptoms.”
Despite being caused by the same bacteria, Lyme disease in dogs and people are very different. The “bulls-eye” rash common in most human cases of the disease is not often reported in dogs. Symptoms usually develop soon after a tick bite in people, while in dogs they arise weeks or months after infection, if at all.
Overview/Snapshot of the Disease
In the United States, the great majority of Lyme disease cases are reported from states in the Northeast, northern mid-Atlantic region, upper Midwest, and northern California coast. The disease is caused by infection with a type of bacteria called Borrelia burgdorferi, which can only be spread by certain types of ticks.
The best host is the deer tick Ixodes scapularis. In far western states (e.g., California, Oregon and Washington), Ixodes pacificus is responsible for transmitting the disease, but this species is not nearly as effective in this role as is its cousin to the east. Therefore, dogs at high risk for developing the disease are those that live in or travel to the aforementioned parts of the country and are likely to be bitten by ticks while in the area.
Lyme Disease Symptoms
Many dogs that are bitten by an infected tick and become infected with Borrelia burgdorferi bacteria do not develop any symptoms. These individuals are able to mount an effective immune response that, although it does not eliminate the bacteria from their body, it does keep the infection suppressed to a level where it is unlikely to cause any harm.
If, however, sufficient numbers of bacteria are able to avoid a dog’s immune system, clinical signs begin to arise several weeks or months after infection. These can include:
- Lameness. Dogs may first favor one leg and then another, or a limp might go away all together only to reappear some time later.
- Swollen lymph nodes
In some cases, long-term infection with Borrelia burgdorferi bacteria can lead to kidney disease.
Borrelia burgdorferi bacteria are usually transmitted from infected wildlife like deer or mice to dogs through the bites of certain types of ticks. When ticks feed, they inject enzymes brought up from their guts to prevent the formation of blood clots. If a tick has previously fed on a Lyme-infected host, the bacteria will be transmitted along with these substances when it bites a different animal.
For bacteria to be passed on to your dog, a tick needs to be attached to his skin for at least 48 hours. If the tick is removed before this time, the chance of a dog becoming infected is very low. However, Ixodes ticks are extremely small and are often overlooked even if a dog is thoroughly checked by his owner.
Lyme Disease Treatment
Veterinarians can usually diagnose Lyme disease based on a dog’s history, clinical signs, a physical exam, tests that reveal exposure to Borrelia burgdorferi, and additional procedures that can help eliminate other potential causes of a dog’s symptoms.
Once diagnosed, a two or three week course of an inexpensive antibiotic is very effective at suppressing bacterial numbers to the point where a dog’s own immune system can regain control and the symptoms of the disease resolve. Unfortunately, some of these dogs can still go on to develop kidney disease in the future.
Avoiding tick bites is the best way to prevent your dog from contracting Lyme disease. Many different safe and effective tick control products are available through veterinarians or pet supply stores. Preventative vaccines are also available and can be useful for dogs that live in or travel to parts of the country where this disease is very common.