Lyme Disease

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 transmits it to large mammals as an adult. Lyme disease therefore occurs when domestic animals and humans enter areas of tick habitat.

Pathophysiology

• • Pathogenesis
    • Virulence of the borreliae requires a change in expression of an outer membrane protein following ingestion of blood by the tick
    • Borreliae multiply in the blood stream of susceptible hosts and disseminate throughout the body
    • Localisation in joints, brain, nerves, eyes and heart can occur
    • The associated lesions may be in part caused by the host immune response

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

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

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