Heartworm disease in a dog results from the infestation of a 14" long worm, Dirofilaria Immitis, a parasite that lives in the right side of the heart and blood vessels of the lungs. Wild and domestic canids (a family of carnivorous mammals that includes dogs, wolves, jackals, and foxes) are the natural host, but other species can be infected. All ages of dogs are susceptible to Heartworm infestation. Outdoor dogs are up to five times more likely to become infected and most studies suggest that males are up to four times more likely to become infected than females.Heartworms require two hosts to reproduce. The dog is the primary host. It carries the adult worms in the heart and lungs and the first stage larvae (microscopic babies), called microfilaria, in the bloodstream. The mosquito is the intermediate host and carries two larval stages. Female mosquitoes become infected after feeding on microfilaria positive dogs. Microfilariae then develop within the mosquito and can infect another dog within 2 to 2 ½ weeks. Heartworms can only be transmitted from animal to animal by mosquitoes. Dogs become infected by getting bitten by a female mosquito carrying the larval stage of the heartworm. After being bitten by an infected mosquito the larvae migrates through the dog’s tissues until it reaches the dogs heart. It takes 6 to 7 months from mosquito bite to adult worm in the heart and lungs.
Dogs can be infected with heartworms for some time and appear completely normal. Often times the first sign of the disease is coughing. Other more serious signs can be:
- Reduced ability to take long walks
- Difficulty breathing
- Weight loss
- Fainting or collapse without loss of consciousness
- Manifestations of right-sided congestive heart failure (swelling of the abdominal cavity, enlarged spleen).
Testing for heartworm is simple. It requires a blood test with results available within 15 minutes. If this screening test is positive, a confirmation test is sent to our reference lab.
Heartworm disease is preventable: After your dog is tested negative for the heart worm, you will start your pet on a once monthly medication, Sentinel. This medication will kill any larvae that are migrating through the dog's tissues before they can reach the heart. This medication is very safe and effective, and also will help control other parasites. Treatment is done year round and testing is performed once a year.
Heartworm disease is treatable: If your dog tests positive for heartworm, a thorough evaluation would be made to stage the severity of the disease. X-rays of the chest and bloodwork would be done. Treatment would begin immediately to kill the adult worms. After killing the adult worms, the circulating microfilaria is then killed using the once monthly preventative.
A last point: Treatment is done with a medication that is a poison (organic arsenical). The worms are lodged in the heart and lungs and the dead bodies have to dissolve over time. This can cause blockages and lung irritation. Treatment can cause death. Untreated heartworm disease can also result in the death of your pet. On the other hand, prevention is easy, very safe and relatively inexpensive.
HEARTWORM DISEASE IN DOGS
By Dr. Terri Lamp, DVM
JULY 2010
