Again, you MUST learn your drugs. January 1999 was icy and cold. The practitioner was amazed that the dog would break with a bloody diarrhea caused by the parasite depicted in the micrograph. The dogs have been defecating indoors and there are infective larvae in the carpet that infected this dog via skin penetration. The dog is regularly reinfected via 'larval leak,' but controlled through most of the year because the heartworm prophylaxis also controls hookworms.
Clinical signs develop after several months after the withdrawal of heartworm prophylaxis.
The phenomenon of 'larval leak' is seen only in females prior to parturition. The dog was probably carrying a patent infection all along and the vet checked a fecal sample only when the owner noticed bloody stools. The dog should be examined for an immunosuppressive condition because this type of infection is almost exclusively seen in neonates or young dogs, thus this patent infection should be considered indicative of another underlying disease process. As a veterinarian, this will be one of the reasons to use certain monthly prophylaxis regimens year-round. I removed 5 points if you thought the dog needs to be checked for an immunosuppressive condition.