Which of the following is a common parasite that affects dogs?

Heartworm is a common parasite that affects dogs, specifically caused by the parasite Dirofilaria immitis. This parasite is transmitted through mosquito bites and can lead to severe health issues in dogs, including damage to the heart and lungs, which may ultimately be life-threatening if left untreated.

In terms of prevention and management, awareness of heartworm and the use of preventative medications are essential for dog owners, especially in regions where mosquitoes are prevalent. The capacity for heartworm to cause significant health problems makes it a primary focus for veterinarians and pet owners alike.

The other listed options, while related to canine health, do not fall into the category of parasites. Parvovirus and canine distemper virus are viral infections, whereas Leptospira is a bacterial infection. These conditions pose serious health risks but differ fundamentally from parasitic infections like heartworm.