Testing for Sarcocystis infections and related disease

Testing the horse with suspect EPM should yield values that assist in treatment decisions.  The IFAT shown in the photo is a positive result.  That doesn’t necessarily mean this horse should be treated with anti-protozoal medications!  Our study that defined relapses attributed to EPM categorized three diseases that have three different treatments. The diseases warrant different treatment because horses may have a one-time exposure or  be chronically exposed. Post-disease conditions that leave the animal with signs due to inflammation are also treated differently.

Sarcocystosis can be caused by S. neurona or S. fayeri.  Some horses are chronically exposed to Sarcocystis in the environment and continued exposure will result in new disease.  These cases are often interpreted as relapses. Disease in horses can be managed and prevented if the correct process is recognized.  The reagents we use to measure S. neurona allow us to determine if a horse has active disease, relapsing disease due to chronic exposure, or signs due to another condition.

Similarly, disease due to S. fayeri can be resolved and prevented if there is suspected environmental exposure.  About thirty percent of horses have S. fayeri and it is usually harmless, horses don’t show disease.  However, some horses do have disease or sub-clinical disease associated with S. fayeri.  We measure the toxin associated with disease-causing fayeri cyst and associate disease with the CRP test.  The CRP allows us to give significance to the presence of S. fayeri  toxin and determine if the infection is due to re-exposure.

The most important criteria in evaluating a horse before, during, and after treatment is the gait score or the presence of signs that indicate disease.  Lab values are important and give insight into the disease process.  The trend. obtained from repeating lab testing, has the most significance in long term case management.  Combined, signs and test results are a valuable method to manage horses.

Quick reference for sarcocystosis testing in a horse that improved with treatment:

S. neurona antibody declined after treatment, CRP trending to normal: indicates that the horse does not have repeat exposure to S. neurona in the environment.  MONITORING THE HORSE FOR CLINICAL SIGNS IS SUFFICIENT.

S. neurona antibody declined after treatment, CRP elevated: indicates that the horse does not have repeat exposure to S. neurona in the environment and there is another disease process. FURTHER TESTING TO DEFINE THE DISEASE PROCESS IS NEEDED.  TESTING FOR S. FAYERI TOXIN, LYME, OR AUTOIMMUNE DISEASE IS USEFUL. DEWORMING TO REMOVE ENCYSTED SMALL STRONGYLES IS USEFUL IN A FEW CASES.

S. neurona antibody increased within 1 month after treatment, CRP trending to normal: indicates that the horse may not have repeat exposure in the environment and responded to the elimination of parasites. A RISE IN TITER IS NOT UNUSUAL, ANTIBODIES WILL REMAIN FOR 5-8 MONTHS. RETESTING THE S. NEURONA SAG’S AT 6-9 MONTHS IS USEFUL.

S. neurona antibody increased after treatment, CRP elevated: indicates that the horse does have repeat exposure in the environment or there is another disease process. FURTHER TESTING TO DEFINE THE DISEASE PROCESS IS NEEDED.  TESTING FOR S. FAYERI TOXIN, LYME, OR AUTOIMMUNE DISEASE IS USEFUL. DEWORMING TO REMOVE ENCYSTED SMALL STRONGYLES IS USEFUL IN A FEW CASES.

S. fayeri antitoxin declined after treatment, CRP trending to normal: indicates that the horse does not have repeat exposure in the environment.   MONITORING THE HORSE FOR CLINICAL SIGNS IS SUFFICIENT.  If the horses was treated for 6 months for S. fayeri the horse can discontinue treatment.

S. fayeri antibody declined after treatment, CRP elevated: indicates that the horse does not have repeat exposure to S. fayeri in the environment and there is another disease process. FURTHER TESTING TO DEFINE THE DISEASE PROCESS IS NEEDED.  TESTING FOR S. FAYERI TOXIN, LYME, OR AUTOIMMUNE DISEASE IS USEFUL. DEWORMING TO REMOVE ENCYSTED SMALL STRONGYLES IS USEFUL IN A FEW CASES.

In our testing/treatment protocol we will not see an increase in S. fayeri antibody after treatment to indicate acute disease was resolved. The anti-toxin is a response to cysts that produce toxin. The CRP is the indicator of disease.

The last disease process that is related to sarcocystosis is inflammation.  Chronic neuromuscular inflammation is polyneuritis.  Pathologic inflammation can be related to new or old disease.  That will be the final topic in this series.  Stay tuned.