EQUINE | CPD Article
occurring most commonly.
• Localization in joints results in arthritis (weeks or
years after the acute phase of the disease).
Timecourse
• Local infection occurs within hours of tick
attachment.
• Due to a paucity of information the period until
clinical signs occur is not known.
• Arthritis may not occur until weeks or years after the
acute phase of the disease.
Epidemiology
• Risk of infection from ticks is highest in the spring,
early summer and autumn, in areas of woodland and
forest where the vector and host most commonly
live.
• Larval ticks hatch and feed on infected rodents,
then transmit the infection to a new host. Deer are
the predominant host for adult ticks, with horses
acting as incidental hosts.
Diagnosis
Presenting problems
• General malaise.
• Pyrexia.
• Single/multiple joint arthritides.
Client history
• Resident in geographic areas with suitable vectors.
• Dull, depressed, pyrexic.
• One/several swollen joint(s).
• Stiffness/lameness.
• Uveitis.
• Neurological disease, including ataxia and central
disturbances.
Clinical signs
• Pyrexia.
• Lymphadenopathy.
• Pseudolymphoma at the site of tick attachment.
• Swollen and painful joint(s).
• Stiffness.
• Lameness, including multiple legs.
• Hyperesthesia.
• Cardiomyopathy (rare).
• Anterior uveitis (rare).
• Neurologic signs of encephalitis.
• Hepatitis.
Diagnostic investigation
Serology
• ELISA or indirect immunofluorescence serum
antibody levels - ELISAs have high false positive
rates and some kits are species-specific - check with
the lab.
• Most ELISAs are based on the C6peptide antibodies
consistent with B. burgdorferi exposure rather than
infection.
• Early in the disease antibody titers may be
undetectable.
• Positive antibody levels do not distinguish between
clinical cases and inapparent infected individuals
(exposure), especially in enzootic areas. Up to 58%
of horses in northeastern US may be serologically
positive, depending on the region.
• Western blot is more specific for serologic assays.
Bacteriology
• Culture of the organism is rarely performed because:
○○
Difficult and requires enriched selective media.
○○
Inoculate with blood or cerebrospinal fluid.
○○
Slow growing.
40 • Equine Health Update •