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Heartworm Facts

Drs. Foster & Smith Educational Staff
Dewormer Comparison Chart 
Dog Heartworm: Risky to Treat; Prevention is Key 
Dog Deworming Guidelines 
Facts you may not know about Heartworm
  • The mosquito is the only known vector for transmitting heartworm.

  • The average lifespan of heartworms in untreated pets is 5-7 years in dogs and 2-4 years in cats.

  • Virtually 100% of dogs exposed to infective heartworm larvae become infected; in cats, this number drops to 61% to 90%.

  • According to the Companion Animal Parasite Council, mature heartworms in cats average 21 cm (about 8.5") in length, while those in dogs average longer than 26 cm (10").

  • Heartworm infection in cats exists everywhere heartworm in dogs exists.

  • A study performed at North Carolina State University indicated that 25% of cats infected with heartworms were solely indoor cats.

  • Heartworms may infect more than 30 species of animals including coyotes, foxes, wolves and other wild canids, domestic cats and wild felids, ferrets, marine mammals, and humans.

  • Prevention is far more effective and less costly than treatment.

  • More than 70 species of mosquitoes are capable of transmitting heartworm.

  • Heartworms cannot be passed directly from one pet to another.

  • Many dogs recover from heartworm disease, but heartworms cause severe disease and sometimes permanent damage.

  • In cats, there is no effective treatment to kill heartworms.

  • Animals will usually test positive for heartworm disease approximately 6-8 months after they were bitten by an infected mosquito.

  • It is much more difficult to diagnose heartworm disease in cats than in dogs.

  • Heartworms affect cats differently than dogs, but the disease they cause is equally as serious.

Heartworm Frequency Map Courtesy the American Heartworm Society

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