Gray fox (Urocyon cinereoargenteus) identified as a new intermediate host for Sarcocystis neurona.

This research identifies the gray fox as a new intermediate host for the disease-causing protozoan, Sarcocystis neurona, which has been known to cause significant illness in horses, marine mammals, and other animal species. The results were concluded through a detailed investigation on 46 gray foxes from Pennsylvania, USA, applying various microscopy and molecular techniques to confirm the presence of Sarcocystis neurona.

Introduction and Background

• Sarcocystis neurona is a harmful parasite that causes acute illness in a wide range of animal hosts in North America, particularly horses and marine mammals.
• The parasite requires an intermediate host to complete its lifecycle. Previously identified primary intermediate hosts in the U.S. include raccoons with the Virginia opossum identified as the definitive host. Canids, or members of the dog family, were not considered significant hosts in the past.

Materials and Methods

• The study involved investigation of 46 gray foxes from Pennsylvania. The presence of Sarcocystis neurona was determined by identifying muscular infections, which represent an essential part of the parasites’ life cycle.
• Various diagnostic methods were used: A microscopic study of muscle tissue sections stained with hematoxylin and eosin (HE), studies of unstained muscle squashes, and electron microscopy.
• Identification of the parasite was confirmed by molecular characterization using a range of genetic markers including 18S rRNA, 28S rRNA, cox1, ITS1, and others.

Results

• 23.9% (or 11 out of 46) of the gray foxes were identified to have Sarcocystis neurona muscular infections.
• Although only 13 sarcocysts were detected in stained muscle sections of 7 out of 46 foxes, unstained muscle squashes revealed the presence of 44 sarcocysts.
• The sarcocyst observed was of a single morphological type, corresponding to S. neurona observed in other animals. The sarcocyst walls were detected to be up to 2.7 μm-thick and contained finger-like protrusions, a characteristic feature of S. neurona.
• Molecular analysis confirmed the presence of S. neurona, with high compatibility to the genetic markers known to identify the parasite.

Conclusions

• This study marks the first reported case of muscular sarcocysts of S. neurona in gray foxes.
• The findings alter our understanding of the life cycle of S. neurona, placing the gray fox as a new intermediate host. The exact role of gray fox in the transmission and epidemiology of S. neurona’s disease should be further studied.