Sporocysts of Sarcocystis bertrami (syn. Sarcocystis fayeri) shed by dogs: Molecular analysis, morphometry and pattern of excretion.

Overview

• This research investigated the shedding of Sarcocystis bertrami (also known as Sarcocystis fayeri), a parasite infecting horses and donkeys, by experimentally infected dogs.
• The study confirmed the presence of the parasite in dog feces using molecular techniques and described the parasite’s morphology and shedding pattern over time.

Background

• Sarcocystis bertrami is a coccidian parasite known to infect equines (horses and donkeys).
• Dogs serve as the definitive hosts, meaning the parasite completes a key stage of its lifecycle inside dogs.
• Previous work had not clearly defined the patent period—the time during which infected dogs shed parasite stages (sporocysts) in their feces.
• The parasite’s identity in dog feces had never been confirmed by molecular methods before this study.

Objective

• To investigate the shedding dynamics of S. bertrami by experimentally infected dogs.
• To perform morphological and molecular analysis of the excreted sporocysts and oocysts.

Methodology

• Three small breed dogs (one Yorkshire terrier and two miniature Pinschers) aged 30 to 60 days were acquired and fed exclusively commercial dog food initially.
• Two dogs were experimentally infected by feeding them equine muscle tissue containing S. bertrami cysts.
• One dog served as a negative control and was fed only commercial dog food.
• Feces from the infected and control dogs were regularly monitored for the presence of Sporocysts and oocysts.
• Morphological measurements of the sporocysts were taken.
• Polymerase Chain Reaction (PCR) tests targeted the 18S ribosomal RNA gene and the Internal Transcribed Spacer 1 (ITS1) region of rDNA from sporocyst DNA extracts.
• Sequences were compared to reference S. bertrami sequences to confirm identity.

Key Findings

• The two infected dogs began to shed sporocysts and/or oocysts after prepatent periods of 13 and 23 days respectively. The control dog did not shed any parasite stages.
• The patent periods—the duration over which shedding occurred—were 47 days for one dog and 14 days for the other. The longer patent period observed (47 days) is notable given it exceeds reported durations for related parasites.
• Sporocysts had an average size of approximately 14.19 µm by 10.06 µm, consistent with previous descriptions.
• Molecular analyses successfully amplified the 18S rRNA gene and ITS1 region from sporocyst DNA, confirming the identity of the parasite as S. bertrami, although some sequence diversity was noted.
• Attempts to PCR amplify the mitochondrial cox1 gene from sporocyst DNA were unsuccessful.
• Because of the genetic diversity and PCR results, the researchers suggest that the presence of a second, undescribed Sarcocystis species in the excreted sporocysts cannot be ruled out.

Significance

• This study provides the first molecular confirmation of S. bertrami in dog feces, solidifying dogs’ role as definitive hosts for this parasite.
• The knowledge of the parasite’s patent period and shedding pattern helps understand parasite transmission dynamics.
• Combination of morphological measurements and molecular data aligns with previous descriptions for both S. bertrami and its synonym S. fayeri, supporting their synonymy.
• Data contribute to veterinary parasitology by clarifying lifecycle details that may impact disease control in equine populations.

Conclusions

• Dogs infected with S. bertrami begin shedding infectious parasite stages roughly 2-3 weeks post-infection, with shedding lasting up to 47 days in one case.
• Molecular tools confirmed the parasite’s identity in feces for the first time.
• The findings improve understanding of Sarcocystis bertrami epidemiology and could impact strategies to prevent transmission to equines and possibly other animals.
• The study raises the interesting possibility of other related Sarcocystis species being involved, highlighting the need for further research.