This Japanese study (scroll halfway down the PDF document to read) follows the illness of 11 people who consumed horsemeat obtained from a market in Japan, with one incident directly traced to Canada. The sarcosystis parasite was detected in the horsemeat. This parasite is the cause of equine protozoal myeloencephalitis (EPM) in horses in North America. The opossum is the definitive host, with the horse being the dead-end host of Sarcocystis neurona. The Japanese study doesn’t say that the horses had EPM, since EPM is the disease of a live animal, not a meat product.
The inference here is that horses shipped live from Canada may have been exposed to the parasite as a result of close proximity to opossums. It is likely that the horses ingested infective opossum sporocysts with feed or water. Opossums are omnivores, and are attracted to grains, moist or dry cat or dog food, fruit or garbage. Therefore, horse feed and pet food should not be left out and open feed bags and garbage should be kept in closed galvanized metal containers.
While it’s possible that the disease could have been acquired while the horses were on feedlots in Japan, it seems more likely that the protocols for proper storage of hay and feed, the control of opossums on the property, or prompt disposal of animal carcasses may not be adhered to for these “feeder” horses while resident in Canada. Opossums are found in Western Canada and the CHDC has previously identified shipments of live horses being sent from YYC (Calgary) airport to Japan.
For further reading:
USDA – EPM/Sarcocystis neurona – http://www.ars.usda.gov/Main/docs.htm?docid=11028
Equine Protozoal Myeloencephalitis: A Report of Two Cases From Western Canada – http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1790025/