Heartworm disease is a life-threatening condition in dogs. The disease is caused by parasitic worms that
grow up to 16 inches long and live in the blood vessels between the heart and lungs of dogs. The worms
are transmitted by mosquitoes and dogs in our area are at risk all year round. Infected dogs can get
changes in the heart that cause heart failure (even years after the disease is treated), inflammatory lung
disease, and can serve as a reservoir for mosquitoes to spread infection more. Untreated disease will
cause death.

The treatment for heartworm positive dogs is relatively expensive and can be deadly to the dogs as well.
It requires 2-3 injections of a medication and by 6 weeks of very restricted activity. As the worms die,
they can break off into little pieces. These can form clots in the lungs and other organs and can create
severe inflammatory disease.

Heartworm is still prevalent in our area, with 68 dogs in Santa Clara County testing positive in the
last year according to the Companion Animal Parasite Council website (petsandparasites.org). Also,
about 40% of wild dogs (coyotes, wolfs, foxes) in the Santa Cruz mountains are positive for heartworm.
Preventing heartworm is a good thing to do for your own pet, but also is good for the rest of the dogs in
the community.

Heartworm disease can be tested for in a number of ways, the most common of which is a simple
and inexpensive blood test. At LAVC we recommend every 2 year testing for dogs that are on a
preventative, and a test must be performed on any dog over 6 months old before starting prevention.
In dogs that test positive, we will often do a confirmatory blood test, X-rays of the thorax (chest) and
ultrasound of the heart before starting treatment.

Infection is easily prevented in our pets with any of a number of good monthly oral medications – and
often these preventatives are combined with flea control medications for more complete parasite
prevention. You can ask any staff which may be the best choice of preventative for your dog’s lifestyle
and your pocketbook.