Lyme disease (Proceedings)
By: Stephen C. Barr, BVSc, MVS, PhD, DACVIM
In the USA, caused by spirochete Borrelia burgdorferi – it is the most common tick-transmitted zoonotic diseases in North America. Although 95% of exposed dogs remain asymptomatic, the main clinical features in dogs include recurrent lameness due to arthritis (sometimes accompanied fever, anorexia and depression). Rarely, renal failure (due to immune mediated glomerulonephritis) can occur.Cardiac, neurologic, and dermatologic disease has also been attributed to Lyme disease but not shown in experimental models. Horses, cattle, and cats can be infected – clinical disease in cats has not been reported.
Transmission – by Ixodes ticks: I. scapularis in the Northeast and Midwest; I. pacificus in the West. In particularly the coastal regions of Northeastern states (CT, NY, RI), the infection rate of I. scapularis ticks with Borrelia can be 50-90%. Tick larvae and nymphs feed on small mammals (mice); adult ticks feed on deer and larger mammals. Infected nymphs and adult ticks attach to dogs and pass on Borrelia while feeding. Because the bacteria lives in the mid-gut of the tick, and must migrate to the salivary glands of the tick for transfer to the skin of a host , transmission does not occur at least for the first 24 hours after attachment – some suggest this is as long as 36-48 hours. The presence of small, flat, non-engorged Ixodes ticks on a dog suggests a very low risk of infection.
Dogs, occasionally horses and cattle, show signs; cats are exposed but signs not reported.Any dog breed exposed may become infected but Shetland Sheepdogs, Labrador and Golden Retrievers have been more likely than other breeds to develop Lyme nephritis. Adult dogs experimentally infected with B. burgdorferi did not develop clinical signs; 6-26 week-old-puppies were more likely to develop disease experimentally. Any age dog may be infected after natural exposure. No gender differences have been reported.
Important to remember that 95% of exposed dogs remain asymptomatic. Acute form – transient fever (103 – 105F), anorexia, depression, and acute lameness lasting for only 3–4 days; reoccurs days to weeks later in the same or in other limbs (shifting lameness); one or more joints may be swollen and warm; a pain response is elicited on joint manipulation; responds well to antibiotic treatment.
Chronic non-erosive polyarthritis found in animals with prolonged infection without adequate treatment; may persist despite antimicrobial therapy. Superficial lymph nodes close to the infecting tick bite may be enlarged. Kidneys – reported glomerulonephritis with immune-complex deposition in the glomeruli leading to fatal renal disease; patients may present with renal failure (vomiting, diarrhea, anorexia, weight loss, polyuria/polydipsia, peripheral edema or ascites); unknown why some dogs develop nephropathy while others do not. Cardiac and neurologic complication – rare clinical reports.