Lyme disease is a chronic, multisystemic, inflammatory disorder of man and animals associated with infection by the tick-borne spirochaete, Borrelia burgdorferi. There are a number of subspecies of Borrelia burgdorferi, each adapted to a different type of wildlife. The principal vector in the UK is the tick Ixodes ricinus and animals become infected following a bite from an infected nymph or adult (Simpson 2008).

In dogs Lyme disease most often manifests as a non-erosive inflammatory arthropathy. The typical presenting signs are a migratory arthritis affecting up to 5 joints (true polyarthritis is rare). Episodes of lameness typically last only a few days, although repeat episodes may occur. There may be fever and lymphadenopathy. Lyme disease has also been associated with a rapidly progressive renal failure and although a causal relationship with Borrelia burgdorferi infection has not been proven an immune mediated glomerulonephritis has been postulated. The risk of developing Lyme associated renal disease appears to be higher in Labradors and Golden Retrievers as well as Bernese Mountain Dogs (Krupka and Straubinger 2010).

Although cats have been found to have similar rates of sero-conversion to dogs clinical signs of Lyme disease are generally absent (May, Carter et al. 1994).

Diagnosis may be difficult and normally depends of evidence of exposure along with clinical signs and diagnostic tests. Tests for Borrelia burgdorferi can be divided into those that demonstrate presence of the organism and antibody tests. Detection of the organism by culture, cytology, or polymerase chain reaction (PCR) assay can be difficult as the organism is difficult to culture and very rarely found in blood, urine, joint fluid or CSF (Littman, Goldstein et al. 2006).

Serological testing is helpful, but subclinical infections can occur, and antibodies to B. burgdorferi may cross react with other spirochaetes. A positive serological test does not equate to a diagnosis of Lyme disease, but animals with clinical Lyme disease are unlikely to be negative for anti-Borrelia antibodies. The cytological changes in synovial fluids from dogs with Lyme disease are often more typical of low-grade immune-mediated joint disease than of a bacterial infection (Ramsey and Tennant 2001).

Treatment
A response to treatment with tetracyclines or penicillin derivatives is normally found within 7 days of starting therapy, but it is advisable to continue antibacterial treatment for at least 2 weeks after the resolution of all clinical signs. Most cases have an excellent prognosis, particularly if diagnosed and treated promptly (Ramsey and Tennant 2001). The ACVIM guidelines recommend that seropositive dogs with clinical abnormalities thought to arise from Lyme disease are treated with doxycycline (10 mg/kg q24h for 1 month). Proteinuric dogs may need longer treatment as well as treatment for protein-losing nephropathy (Littman, Goldstein et al. 2006).

Prevention
There is no licensed vaccine available for Lyme disease in Europe but even in the USA where a vaccine is available ACVIM diplomates consider the use of the vaccine controversial. There is evidence that acaricides prevent transmission of Borrelia as during the first 12 to 24 hours after the tick bite, borrelia organisms residing in the tick’s midgut are not transmitted to the vertebrate host (Spencer, Butler et al. 2003; Jacobson, McCall et al. 2004; Krupka and Straubinger 2010) .

However it should be remembered that tick repellents may be necessary for the prevention of other tick-borne diseases.

See also How to... pick your way through the jungle of ectoparasite treatments for dogs and cats companion January 2012

Human health implications
Lyme disease in humans can take many forms and may mimic a wide range of conditions. Clinical signs include a characteristic circular red rash, erythema migrans, which spreads from the site of the tick-bite, followed by a flu-like condition. If untreated, the disease can progress to neurological problems and arthritis.

Further information
NHS website
Health Protection Agency website

References

• Couper, D., G. Margos, et al. (2010). "Prevalence of Borrelia infection in ticks from wildlife in south-west England." Veterinary Record 167(26): 1012-1014.
• Hendricks, A. and N. Perrins (2007). "Recent Advance in tick control." In Practice 29(5): 284-287.
• Jacobson, R., J. McCall, et al. (2004). "The ability of fipronil to prevent transmission of Borrelia burgdorferi, the causative agent of Lyme disease to dogs." Journal of Applied Research in Veterinary Medicine 2(1): 39.
• Krupka, I. and R. K. Straubinger (2010). "Lyme Borreliosis in Dogs and Cats: Background, Diagnosis, Treatment and Prevention of Infections with Borrelia burgdorferi sensu stricto." The Veterinary clinics of North America. Small animal practice 40(6): 1103-1119.
• Littman, M. P., R. E. Goldstein, et al. (2006). "ACVIM Small Animal Consensus Statement on Lyme Disease in Dogs: Diagnosis, Treatment, and Prevention." Journal of Veterinary Internal Medicine 20(2): 422-434.
• Ramsey, I. K. and B. J. Tennant (2001). BSAVA Manual of canine and feline infectious diseases, British Small Animal Veterinary Association.
• Simpson, V. (2008). "Wildlife as reservoirs of zoonotic diseases in the UK." In Practice 30(9): 486-494.
• Smith, F. D., R. Ballantyne, et al. (2012). "Estimating Lyme disease risk using pet dogs as sentinels." Comparative Immunology, Microbiology and Infectious Diseases.
• Spencer, J. A., J. M. Butler, et al. (2003). "Evaluation of permethrin and imidacloprid for prevention of Borrelia burgdorferi transmission from blacklegged ticks (Ixodes scapularis ) to Borrelia burgdorferi -free dogs." Parasitology Research 90(0): S106-S107.

Image credit © Michael Pettigrew