It looks like a parasitic nematode or worm of some kind. Maybe a Strongyloidiasis stercoralis. Dogs can be a host. I don't think it is a contamination issue, but you might draw another sample to check.

Thank you, Cathleen Doyle. Indeed, we collected two additional blood samples from the same dog at different intervals and from other dogs residing in the same household. Surprisingly, we found no evidence of any nematodes in those samples. This discrepancy leads me to suspect contamination, possibly from feces, with Strongyloides being one of the potential culprits.