What is heartworm disease?

Heartworm disease results from infection with Dirofilaria immitis, a parasitic worm spread by mosquitoes. Infected mosquitoes transmit larvae to dogs and cats during feeding. Over months, these larvae develop into adult worms that lodge in the heart and pulmonary arteries, causing inflammation and reducing blood flow.

The infection damages the heart's ability to function and can lead to congestive heart failure, organ damage, and death if left untreated. Early detection matters because treatment becomes more difficult and riskier the longer worms remain in the body. Dogs are at higher risk than cats, though both species can contract the disease.

Veterinarians detect heartworm through antigen tests, which identify proteins produced by adult female worms in the bloodstream. These tests are reliable but work best after worms reach maturity, typically six months after infection.

Prevention is far more effective than treatment. Monthly preventives, available as oral medications or injectables, stop larvae from developing into adult worms. Consistent year-round use protects pets from infection, even during Austin's warmer months when mosquitoes are active. A general practice veterinarian can recommend the right preventive for your pet's age and health profile and monitor for infection through regular testing.