Dog Heartworm

Overview & History: 

Heartworm is a potentially fatal condition caused by a filarial nematode (Dirofilaria immitus) that invades and occupies the canine heart and pulmonary arteries. Dogs and coyotes are most susceptible to infection, but cats and occasionally other mammals may also be affected. The parasitic worms are transmitted by the bite of an infected mosquito. Although certain areas may have a higher incidence of heartworm than others, the disease has been reported in all 50 states.

Impact on human health: 

Dog heartworm is primarily a disease of veterinary importance. Although human infections have been occasionally reported, humans are not the natural hosts for heartworms.

What you can do to protect yourself: 
  • Consult your veterinarian about the various options available for prevention of dog heartworm.
  • Successful treatment of infected dogs is possible, but may be expensive and require weeks for recovery. There are currently no effective means of treatment for infected cats, so prevention is of utmost importance. 
  • Prevent mosquitoes from growing near your home:
  1. Flip, dump or drain all temporary sources of standing water.
  2. For more information, read our "Are you Raising Mosquitoes?" brochure. 
  3. Call Marin/Sonoma Mosquito & Vector Control District if you have a mosquito-related problem that you cannot resolve on your own.
Impact on animals/wildlife: 
  • Early clinical signs of heartworm may be difficult to detect, but heavily infected animals may exhibit a variety of symptoms that include, but not limited to: coughing, lethargy, reduced appetite, and weight loss.
  • If left untreated, heartworm may be fatal to both dogs and cats.