Lyme disease is one of the most common of all infectious diseases transmitted by ticks. It affects domestic dogs and other mammals, including people, when they are bitten by infected ticks. Lyme disease has been reported on most continents and can cause very severe illness. The ticks that carry the infective bacteria prefer to live in warm, or temperate, climates. Lyme disease was first officially identified in people in 1975, as a result of an acute outbreak of arthritis in several rural Connecticut communities. One of these was the town of Old Lyme, located in the southeastern part of the state. In the United States, Lyme disease occurs mainly in wooded areas of the mid-Atlantic to northeastern coastal states, and in northern California, the upper Midwest (especially Wisconsin and Minnesota) and the coastal Pacific Northwest. Most cases of Lyme disease are reported from March through October, during the warm months in areas where the ticks that carry this disease live.
Causes of Lyme Disease (Borreliosis)
Lyme disease is caused by a single-celled, spiral-shaped bacterium known as Borrelia burgdorferi. The main reservoir for these bacteria in the United States is the white-footed mouse. The bacteria can also live and replicate inside of other small mammals, lizards and birds. The organisms are transmitted to larger animals by tiny, hard-shelled, slow-feeding ticks. The ticks become infected with the bacteria when they feed on the blood of infected animals – especially the white-footed mouse. Ticks are considered to be intermediate reservoirs for Borrelia burgdorferi. These ticks are also known as "deer ticks," because their preferred host is the white-tailed deer. So, the "bad bugs" like to live inside of the white-footed mouse and other small mammals. The "bad ticks" become infected by feeding on one of these animals, and then eventually transfer the infection of Borrelia burgdorferi to deer, dogs or other larger mammals that they bite.
Dogs develop Lyme disease when they are bitten by an infected immature or adult female tick that feeds on them for a long period of time. There is some disagreement about how long an infected deer tick must be attached to a dog for the infection to be transferred. Some experts maintain that a dog can become infected in as little as 5 hours, while others suggest that the tick must remain attached to the dog for at least 20, 50 or even 70 hours to transmit the infectious microorganisms. In any event, it is clear that infected ticks need to feed on a dog's blood for many hours before they can transfer Borrelia burgdorferi to the dog through the site of the bite. The actual transfer occurs when the tick regurgitates infectious microorganisms into the bite wound in its saliva, after it finishes feeding.
The infective bacteria multiple rapidly in and under the dog's skin around the area of the tick bite, which causes a lot of local irritation and potential infection. People with Lyme disease typically develop a raised, red area at the inoculation site during this initial period of the disease. This is called an erythema migrans. Dogs do not develop these lesions. Within a matter of weeks to months after the bacteria are injected from a tick into a dog, they migrate throughout the dog's body in its bloodstream. The bacteria tend to lodge in the connective tissues of joints, muscles, tendons and other areas that have high collagen content, such as skin, heart and lymph nodes, where they continue to replicate in large numbers.
The bacterial infection triggers an immune response in the dog's body. This, together with the localized concentration of bacteria in and around joints, tendons and muscles, are responsible for the limping and lameness seen in most dogs with Lyme disease.
Prevention of Lyme Disease (Borreliosis)
The only way to prevent a dog from developing Lyme disease is to prevent it from coming into prolonged contact with infected ticks. Because these ticks only regurgitate infective bacteria in their saliva at the end of a long blood meal, Lyme disease can be avoided by preventing ticks from attaching to dogs in the first place. This can be accomplished through appropriate use of repellent sprays, anti-tick collars, dips, powders, dusts and liquid spot-on treatments. Amitraz collars and various topical preparations (such as Frontline, Advantix and others) reportedly are quite effective at controlling ticks. Area treatment with insecticides usually is not necessary. Your veterinarian is the best one to advise you about appropriate tick control protocols for your pet in your geographical area.
Here are some other common-sense ways for owners to protect their dogs (and themselves) from tick bites:
Avoid dense undergrowth. Walk dogs on closely mowed grass, dirt or paved walkways whenever possible.
Wear long-sleeved shirts and long pants tucked into socks when out in endemic areas. Light-colored clothes make ticks more visible and easier to brush or pick off.
Apply topical tick repellent to clothing and exposed areas of skin; apply topical veterinarian-approved tick repellant to all areas of the dog's coat and skin, avoiding only the eyes and mouth.
Inspect dogs thoroughly for ticks immediately after venturing outdoors in areas where ticks are known to be present in large numbers.
Keep lawns mowed and weeds pulled to reduce the number of places for ticks to hide.
Eliminate areas of dense, undisturbed vegetation from areas that the dog has regular access to.
Discourage wild animals (raccoons, skunks, deer, mice, rats and other rodents) from coming into contact with domestic dogs. Wild animals can harbor the ticks that transmit the bacteria causing Lyme disease.
It's a good practice for owners to go over their dog's skin and coat regularly, especially after the dog has spent time outside and has been exposed to dense brush, grass or other thick vegetation. Dogs (and people) who spend a lot of time outdoors should be checked daily for ticks. Unfortunately, immature deer ticks are tiny and can be difficult to detect, especially on dogs with dark coats. Even adult deer ticks are small – about the size of the head of a pin. They can easily be mistaken for freckles, moles or specks of dirt.
It is best to remove ticks before they latch on. However, Lyme disease can also be prevented if a tick is removed after it has attached but before it has finished feeding. If a tick is found, it should be mechanically removed from the dog's body as quickly as possible, using gentle traction. Owners should grasp the tick with tweezers at the point where its mouthparts enter the dog's skin and pull straight outward with firm, constant pressure. Specialized tick-removal devices are also commercially available. Gloves should be worn to prevent contact with the tick's blood. Once removed, the tick should be placed in rubbing alcohol in a sealed container and disposed of in an outdoor garbage receptacle. Tossing a tick into the toilet, or "squishing" it in a paper towel and throwing it into a waste basket, are not reliable disposal methods.
Vaccines against Lyme disease are available for domestic dogs. Currently, these vaccines usually are only recommended for dogs that live in or travel to high-risk areas. Lyme disease vaccines work by preventing migration of the infective bacteria from an attached tick's gut to its salivary glands during the course of the tick's blood meal. Regular booster shots have been shown to improve the protection afforded by Lyme disease vaccines.
Deer ticks have a specialized 2-to-3 year life cycle, depending upon climatic conditions and the availability of host animals for them to feed on. Adult females lay their eggs in warm weather, often in the middle of summer. On average, a single female lays approximately 2,000 eggs. She only does so once during her life. The larvae hatch a few weeks later and can live without feeding for up to 8 months. Larval-stage ticks become infected by Borrelia burgdorferi when they feed on birds or small mammals that carry the bacterial microorganisms. The most common of these is the white-footed mouse. The following spring, tick larvae molt into nymphs. If they were infected by Borrelia burgdorferi as larvae, they will remain infected as nymphs. If they were not infected at the larval stage, they still can become infected at the nymph stage by feeding on the blood of carrier mammals or birds. Nymphs can survive unfed for about 6 months. Infected nymphs molt into infected adult ticks during the following summer months.
Adult female ticks mate and then have a single, prolonged blood meal by attaching to a white-tailed deer or another large mammal. Adult males normally do not attach to or feed off of any animals. Once they come into contact with a host, adult female ticks tend to attach very quickly. Adult females do not feed intermittently; once they start, they almost always continue to feed on the same animal until they are satiated. After they have eaten as much as they can hold, engorged female ticks fall off of their hosts and land in surface vegetation. They live on or under leaves or brush until the following summer, when the cycle begins anew.
There is no reliable evidence that Lyme disease can be passed from an infected bitch to her unborn puppies. Theoretically, transmission of the infective organism through placental blood may be possible.
How Lyme Disease (Borreliosis) Affects Dogs
Most dogs with Lyme disease never show signs of illness. When symptoms do occur, they usually involve limping and lameness, which are caused by pain around the dog's joints. These signs may wax and wane, but they often come back and, if left untreated, progressively worsen with time.
Symptoms of Lyme Disease (Borreliosis)
Most owners never know that their dogs have been infected by Borrelia burgdorferi. In fact, only about 5% of infected dogs become noticeably ill. Dogs that do develop clinical Lyme disease usually show signs between 1 and 5 months after being bitten by an infected tick. Normally, symptoms show up in the spring, summer and fall, when the weather is warmer. The height of tick season in most parts of the United States is March through late September, tending to peak in July. However, deer ticks can survive and be active anywhere and any time that the temperature is above freezing.
Dogs with symptomatic Lyme disease may show one or more of the following symptoms:
Acute onset of lameness (the most common and characteristic observable symptom; polyarthritis; usually lasts only a few days but frequently recurs; may come and go; may be persistent; can become chronic)
Shifting leg lameness (limping changes from leg to leg)
Swollen joints (especially the hocks of the hind legs and the "wrists" [carpi] of the front legs)
Warmness around joints
Painful joints (especially when palpated/moved or manipulated manually)
Reluctance to rise
Reluctance to walk
Stiff, stilted gait
Arched back (when standing or walking)
Fever (variable; usually low-grade but can be elevated)
Enlarged lymph nodes (lymphadenopathy)
Lack of appetite (inappetence; anorexia)
Kidney disease. Severe renal disease has been widely reported in dogs with Lyme disease; when this unique form of kidney damage occurs, it usually presents with progressive vomiting, diarrhea, anorexia, weight loss, increased water intake (polydipsia), increased urine output (polyuria), swelling of the extremities (peripheral edema) and, unfortunately, death
Cardiac (heart) abnormalities (uncommon; severe when present; usually sudden in onset; can be fatal)
Neurological abnormalities (central nervous system consequences of Lyme disease are rare; seizures, facial paralysis and behavioral changes such as aggression have been attributed to Lyme disease in dogs)
Dogs at Increased
Puppies and young dogs are more susceptible to Lyme disease than older animals, although dogs of any age can be affected. Dogs that are allowed to roam freely and primarily live outside, as well as those that are routinely involved in outdoor activities like hunting, have a heightened risk of developing Lyme disease, simply because their chances of coming into contact with infected ticks are greater than those of other dogs. This is especially true if they live in or travel to endemic areas, which are the mid-Atlantic to northeastern coastal states, the upper Midwest and the coastal areas of the Pacific Northwest. Infection is even more likely if the dog moves through dense, undisturbed vegetation in those areas. The risk of infection is especially high when the nymph and adult ticks are actively seeking animal hosts to feed on, which is most common in the hot months of late spring, summer and early fall.
Certain breeds, including the Labrador Retriever, Golden Retriever, Shetland Sheepdog and Bernese Mountain Dog, develop a severe and frequently fatal form of Lyme disease that involves progressive damage to their kidneys. These breed associations suggest that there may be a genetic component to the cause of Lyme disease. However, the reason for these associations is unclear.
How Lyme Disease (Borreliosis) is Diagnosed
Lyme disease in dogs is not easy to diagnose. Most infected dogs are asymptomatic, which means that they have been exposed to and infected by Borrelia burgdorferi but show no outward signs of illness. In addition, dogs with this disease often have other tick-borne ailments, such as ehrlichiosis or babesiosis, which can mimic the signs of Lyme disease. The initial diagnostic focus usually is to rule out other possible causes of lameness and appetite loss in a dog with a fever of unknown origin. In most cases, the veterinarian will make the diagnosis based on the dog's history, physical examination results, observable symptoms, laboratory test results and ruling out other causes of the dog's clinical signs.
The results of routine urine and blood tests are almost always unremarkable in dogs with Lyme disease. A history of recent exposure to ticks, or to heavily vegetated areas known to harbor ticks that carry Borrelia burgdorferi, is important to the diagnosis. A dog's prompt response to antibiotic treatment can also help to confirm that it is suffering from Lyme disease. Radiographs (X-rays) of painful or swollen joints can be used to rule out trauma and some other potential causes of lameness. X-rays of the joints of dogs with clinical Lyme disease typically show accumulated fluid without any fractures or obvious degenerative joint changes.
Specialized testing for Lyme disease is available. The presence of antibodies to the infective bacteria can be detected in blood samples using several different advanced tests. Antibodies usually can be detected several weeks after a dog has been exposed to the bacteria. A positive result on blood tests means that the dog has been exposed to, and has mounted an immune response against, the "bugs" that cause Lyme disease. If the dog has been vaccinated against Lyme disease, the results of blood tests can become more difficult to interpret. A fairly recent test is available that is both convenient and effective in differentiating between a dog's antibody response to natural infection and one caused by a vaccine.
For a number of reasons, blood tests alone usually are not enough to definitively diagnose Lyme disease. Samples of joint fluid taken from dogs with Lyme disease often contain very high numbers of white blood cells. This is a sign of inflammation. The procedure used to get samples of joint fluid is called "arthrocentesis." Unfortunately, evaluation of joint fluid usually does not provide information about the cause of the elevated white blood cell count, unless the bacteria can be identified microscopically.
Although the organisms that cause Lyme disease are somewhat difficult to grow in a laboratory, culture is still the preferred and most reliable way to diagnose Lyme disease. This procedure is usually performed at an outside laboratory on skin samples taken from the infected dog. The laboratory personnel will attempt to grow colonies of Borrelia burgdorferi from those skin samples. If these organisms grow from the skin samples, the culture is considered to be positive, and the diagnosis of Lyme disease is considered to be definitive.
Only about 5% of dogs bitten by infected deer ticks go on to develop observable signs of Lyme disease. As a result, this disease is rarely diagnosed in companion dogs. When a dog is diagnosed with Lyme disease, its owner should be very conscious of the chances that she, too, may be infected. The source of infection for people and for dogs is the same: infected ticks. The fact that a dog develops clinical disease means that it has been to some place where infected ticks are present. Presumably, the owner has also been to that place and may also have been exposed to infected ticks. Ticks that have not attached to a dog can be transferred to people, although this is unlikely because deer ticks usually latch on very quickly to their warm-blooded hosts.
Fortunately, Lyme disease in dogs is usually treatable. Therapeutic goals are to resolve lameness and soreness, relieve fever and pain, eliminate infectious organisms from the blood stream and provide supportive care for dogs with kidney, heart, neurological or other serious complications. Affected dogs should be kept warm, dry and quiet. Their activities should be restricted until their symptoms have been resolved. In most cases, there is no need to change the dog's diet.
Antibiotics are the treatment of choice for most dogs with Lyme disease. Oral antibiotics typically are given for at least four weeks, in strict accordance with a veterinarian's instructions. Amoxicillin and doxycycline have proven effective at resolving symptoms of Lyme disease in many cases. Ampicillin, clavamox, cephalexin and azithromycin are also among the antibiotic options available to treat canine Lyme disease. Newer medications are always being developed, while older ones are being phased out. The exact length of time that antibiotic therapy should be administered to eliminate Borrelia burgdorferi is not known. Steroids, or non-steroidal anti-inflammatory drugs (NSAIDs), may be recommended in some cases. However, they will be used judiciously, because they can mask or sometimes even exaccerbate the symptoms of Lyme disease.
Dogs that develop kidney damage from Lyme disease may need specialized treatment, including longer courses of powerful antibiotics. They also may require hospitalization, anti-nausea medications, intravenous fluids and individualized nutritional support.
Dogs do not develop immunity to the bacteria that cause Lyme disease and can become sick again if another infected tick attaches to them for the requisite period of time. Dogs with heavy tick loads may benefit from periodic shampooing and insecticide dips. Ticks that are embedded deeply in a dog's ear or in other hard-to-reach places probably should be removed by a veterinarian.
The selection and use of any treatment protocol should be made through consultation with the animal's attending veterinarian. While antibiotic treatment usually eliminates the symptoms of Lyme disease and greatly improves a dog's quality of life, antibiotics rarely completely cure this disease. In other words, most dogs with Lyme disease will remain carriers of small amounts of the infective bacteria for the rest of their lives. Fortunately, recurrence of clinical signs from an initial infection is fairly uncommon, although it occasionally does happen.
Most dogs with a sudden onset of the symptoms of Lyme disease respond quite well to antibiotics and begin recovering from their lameness and fever within 2 to 5 days. The prognosis for these dogs is good. However, their symptoms can return. If they do, it usually is several weeks to months after their first bout of symptoms has resolved. Subsequent episodes should respond equally well to treatment with oral antibiotics and should occur with decreasing frequency over time.
The prognosis for dogs that develop kidney problems from Lyme disease is guarded to poor. Unfortunately, sometimes their life expectancy is only days to weeks after their illness is diagnosed.