Lyme Disease
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Description
Lyme disease descibes the clinical syndrome caused by infection with Borrelia burgdorferi in humans, dogs, horses, cattle and sheep. The disease is named after the town of Lyme[1] in Connecticut, USA where clinical cases were first described in humans in 1975.
The bacterium is transmitted by ticks of which the most common is Ixodes ricinus in the UK. I. ricinus is a three host tick that acquires B. burgdorferi bacteria when it obtains a blood meal from small rodents as a larva or nymph and then transmits it to large mammals as an adult. Lyme disease therefore occurs when domestic animals and humans enter areas of tick habitat.
Pathophysiology
The virulence of the borreliae is associated with a change in expression of an outer membrane protein (OMP) after introduction into the mammalian host. The bacteria multiply in the blood stream of susceptible hosts and disseminate throughout the body, loaclising particularly in the joints, brain, nerves, eyes and heart. The immune response to the bacterial OMPs cross-reacts with epitopes present of host proteins and the lesions that are observed in Lyme disease may in part be caused by this immune response.
Signalment
Diagnosis
Clinical Signs
- May be subclinical in endemic areas
- Clinical manifestation depends on the site of localisation of organisms
- Disease in dogs may cause fever, lethargy, arthritis, cardiac, renal or neurological disturbance
- Horses suffer similar clinical signs but also lameness, uveitis, nephritis, hepatitis and encephalitis
- Cattle and sheep may suffer from lameness
Laboratory Tests
Other Tests
- Laboratory confirmation difficult due to low numbers of organisms and fastidious growth requirements
- History of exposure to ticks in an endemic region and clinical signs
- Rising antibody titre to Borrelia burgdorferi detected by ELISA
- Immunofluorescence
- Culture in Barbour-Stoenner-Kelly medium for 6 weeks under microaerophilic conditions
- PCR
Diagnostic Imaging
Treatment
- Amoxycillin and oxytetracycline in the acute phase; prolonged treatment in the chronic phase
- Tick control and removal
- Vaccines including whole cell bacterins and recombinant subunit vaccines available for dogs