By Dr. Patrick Mahaney, VMD
Lyme disease (Lyme borreliosis) is an infectious disease affecting humans, dogs, cats, and other species. This debilitating illness stems from microscopic bacteria called Borrelia burgdorferi, which is transmitted from the bite of an infected tick into an animal host.
Dogs are more commonly infected with Lyme disease than cats, mostly due to their propensity to get out and about to explore grassy or wooded environments where ticks can lurk on leaves, branches, or blades of grass, and latch on to a dog’s coat as it passes by.
As most cats live either primarily or exclusively indoors, they are generally less affected by Lyme disease. Felines living indoor-outdoor lives are more prone to tick bites and infection with Borrelia burgdorferi.
There are a variety of clinical signs that can be found individually or in combinations. If left untreated, Lyme disease can be fatal.
Lameness (limping) and general problems moving are the most common and sometimes only clinical signs seen in dogs infected with Lyme disease. Shifting leg lameness (i.e., standing with more weight on one limb, then shifting to another limb), exercise intolerance, increased sitting or lying down, or discomfort when an affected joint is taken through range of motion from Lyme-related arthritis (joint inflammation) or myalgia (muscle pain) are all associated with Borrelia burgdorferi infection.
Dogs infected with Lyme disease are more lethargic, which means they will act more tired instead of being awake and energetic. Lethargy occurs as a result of the immune system’s increased efforts to fight the Lyme disease bacteria (Borrelia burgdorferi) through the production of antibodies (immune system proteins) and white blood cells. Body temperature elevation (hyperthermia) is often association with lethargy.
As the immune system of a Lyme disease-infected dog is stimulated to fight infection by Borrelia burgdorferi, hyperthermia occurs. A dog’s normal body temperature ranges between 100 to 102.5 F; Lyme disease leads to intermittent or consistent increases in body temperature.
Associated with hyperthermia can be lethargy, anorexia (lack of appetite), polydipsia (increased water consumption), polyuria (increased urine output), and other signs.
Lyme disease causes anorexia, which can manifest as a decreased appetite to the degree that substantially less food is consumed, or all meals or treats may be completely refused.
Anorexia can be caused by hyperthermia (elevated body temperature), arthritis (joint inflammation), myalgia (muscle pain), renal (kidney) failure, or other ailments associated with infection by Borrelia burgdorferi.
Besides eating less or refusing food, dogs infected with Lyme disease can have other digestive tract upset such as emesis (vomit) or diarrhea related to hyperthermia, renal failure, or other health problems.
While an elevated body temperature (hyperthermia) commonly causes dogs to drink more water (polydypsia), kidney failure occurring secondary to Lyme-disease infection can also stimulate water consumption. More water going in leads to increased urine output (polydypsia).
Failing kidneys have a reduced ability to concentrate urine. Ultimately, this failure prompts the affected dog to drink more water as the body tries to excrete the toxins from the blood that would otherwise normally be filtered by the kidney into urine.
Untreated Lyme disease can result in kidney (renal) failure, and eventually, death.
Dogs infected by Lyme disease may also show symptoms of muscle and joint soreness (arthritis), and if left untreated, may suffer from multiple organ system damage, such as the kidneys, liver, and others.