CPD Article | EQUINE
Cytopathology
• CSF may be able to identify the spirochete, more
likely to see a neutrophilia and hypoproteinemia as
well as submitting the sample for antibody testing
or PCR.
• Synovial fluid analysis:
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In affected joints there is evidence of
inflammation with increased neutrophils and
protein.
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Negative culture.
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PCR positive results are seen.
Histopathology
• Biopsy:
○○
Synovial biopsy: non-specific mononuclear cell
infiltrate in acute cases, with pannus reaction in
chronic cases.
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PCR can be performed on biopsies.
Other
• PCR is available in some labs; done on blood, CSF,
skin biopsy near affected joint, synovial membrane
biopsy is definitive - false negatives occur due to
low concentration of organism/inconsistent levels.
• Multiplex assay developed at the Animal Health
Diagnostic Center, Cornell University. This is a
fluorescent bead-based assay to detect antibodies
to various surface proteins of Borrelia burgdorferi
in CSF and serum. By utilizing the different surface
proteins, a theoretical chronicity of infection can be
established.
• Dark-field microscopy is possible in acute cases
although has not been documented in equine
blood.
• Seroconversion to Anaplasma frequently seen as
the Ixodes tick will often be co-infected.
Confirmation of diagnosis
Discriminatory diagnostic features
• History and clinical signs.
• Horse resides in endemic area.
• Rule out other potential causes.
• Serological evidence for infection. However,
antibodies usually develop 3-6 weeks after infection,
prior to development of clinical signs. Therefore
many horses have already seroconverted at the
time of sampling, so paired titers are not useful. In
addition, many seropositive horses never develop
clinical signs.
Definitive diagnostic features
• Culture of organism (very difficult).
• Identification of spirochetes in fluid (CSF, synovial,
ocular).
Gross autopsy findings
• No pathognomonic signs.
Histopathology findings
• In joints:
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Non-specific villus hypertrophy.
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Synovial cell hypoplasia.
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Vasculitis.
○○
Edema.
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Fibrin deposits.
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Lymphoid follicles.
• Lymphohistiocytic nodules in dermis.
• Perivascular and perineural lymphocytic reactions
in skin, fascia and perisynovial membranes.
• May identify the spirochetes in synovial fluid/tissue,
CSF, lymph nodes, renal tissue.
• Volume 22 Issue 02 | June 2020 •
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