Objective—To determine whether antibodies against
Sarcocystis neurona could be detected in CSF from
clinically normal neonatal (2 to 7 days old) and young
(2 to 3 months old) foals.
Animals—15 clinically normal neonatal Thoroughbred
Procedure—Serum and CSF samples were obtained
from foals at 2 to 7 days of age and tested for antibodies
against S neurona by means of western blotting.
Serum samples from the mares were also tested
for antibodies against S neurona. Additional CSF
and blood samples were obtained from 5 foals
between 13 and 41 days after birth and between 62
and 90 days after birth.
Results—Antibodies against S neurona were detected
in serum from 13 mares and their foals; antibodies
against S neurona were detected in CSF from 12 of
these 13 foals. Degree of immunoreactivity in serum
and CSF decreased over time, and antibodies against
S neurona were no longer detected in CSF from 2
foals 83 and 84 days after birth. However, antibodies
could still be detected in CSF from the other 3 foals
between 62 and 90 days after birth.
Conclusions and Clinical Relevance—Results indicate
that antibodies against S neurona can be detected
in CSF from clinically normal neonatal (2 to 7 days
old) foals born to seropositive mares. This suggests
that western blotting of CSF cannot be reliably used
to diagnose equine protozoal myeloencephalitis in
foals < 3 months of age born to seropositive mares.
(J Am Vet Med Assoc 2002;220:208–211)
To determine effects of blood contamination on western blot (WB) analysis of CSF samples for detection of anti-Sarcocystis neurona antibodies, and on CSF albumin and IgG concentrations, albumin quotient (AQ), and IgG index in horses.
Prospective in vitro study.
Blood with various degrees of immunoreactivity against S neurona was collected from 12 healthy horses. Cerebrospinal fluid without immunoreactivity against S neurona was harvested from 4 recently euthanatized horses.
Blood was serially diluted with pooled nonimmunoreactive CSF so that final dilutions corresponded to 10-3 to 100 μl of blood/ml CSF, and WB analysis was performed on contaminated CSF samples. Number of RBC, albumin and IgG concentrations, AQ, and IgG index were also determined.
Antibodies against S neurona were detected in CSF contaminated with 10-3 μl of strongly immunoreactive blood/ml. In CSF samples contaminated with 10 μl of blood/ml, AQ remained within reference range. Volume of blood required to increase IgG index varied among blood samples and was primarily influenced by serum IgG concentrations. Number of RBC in contaminated samples was correlated with volume of blood added, but not with degree of immunoreactivity detected in contaminated CSF samples.
Conclusions and Clinical Relevance
During collection of CSF from horses, contamination with blood may introduce serum antibodies against S neurona at concentrations sufficient for detection by WB analysis, thus yielding false-positive results. When blood is moderately or strongly immunoreactive, the amount of contaminating albumin may be small enough as to not increase AQ above reference range. In these cases, AQ and IgG index should be interpreted with caution. (J Am Vet Med Assoc 1999;215:67—71)
Objective—To determine sensitivity and specificity of
western blot testing (WBT) of CSF and serum for diagnosis
of equine protozoal myeloencephalitis (EPM) in
horses with and without neurologic abnormalities.
Animals—65 horses with and 169 horses without
Procedure—CSF and serum from horses submitted
for necropsy were tested for Sarcocystis neuronaspecific
antibody with a WBT. Results of postmortem
examination were used as the gold standard against
which results of the WBT were compared.
Results—Sensitivity of WBT of CSF was 87% for horses
with and 88% for horses without neurologic abnormalities.
Specificity of WBT of CSF was 44% for horses
with and 60% for horses without neurologic abnormalities.
Regardless of whether horses did or did not have
neurologic abnormalities, sensitivity and specificity of
WBT of serum were not significantly different from values
for WBT of CSF. Ninety-four horses without EPM
had histologic evidence of slight CNS inflammation.
Conclusions and Clinical Relevance—The low
specificity of WBT of CSF indicated that it is inappropriate
to diagnose EPM on the basis of a positive test
result alone because of the possibility of false-positive
test results. The high sensitivity, however, means that
a negative result is useful in ruling out EPM. There was
no advantage in testing CSF versus serum in horses
without neurologic abnormalities. Slight CNS inflammation
was common in horses with and without S
neurona-specific antibodies in the CSF and should not
be considered an indication of CNS infection with S
neurona. (J Am Vet Med Assoc 2002;221:1007–1013)