April is national heartworm awareness month, so it seems like the perfect time for a refresher on the basics of heartworm disease. Heartworm disease is a very serious and potentially fatal disease of pets in the United States and many other countries worldwide. Though states in the southeastern US have the highest incidence, heartworm disease has been identified in all 50 states, so pets everywhere are at risk. Heartworm disease is most prevalent in dogs, but it can also affect cats, ferrets and many wild mammals including wolves, coyotes, foxes and sea lions.
Immature heartworms (larvae) are transmitted by mosquitoes and just one bite from an infected mosquito can transmit the larvae into your pet’s blood stream. These larvae mature over a period of 6 months into adult heartworms. The gory details on the adult worms include that they can be up to a foot in length, can live in a dog for 5 to 7 years, and a single dog can harbor hundreds of worms (yikes!). Adult heartworms live in the heart and pulmonary arteries, causing severe inflammation and affecting blood flow. They cause severe and lasting damage to the lungs and heart muscle, which can lead to heart failure and dramatic respiratory compromise. Much of the damage caused by heartworms does not resolve with treatment, so prevention is incredibly important.
Dogs in the advanced stages of heartworm disease can show significant symptoms including coughing, decreased appetite, lethargy, and labored breathing but it is important to realize that in the early stages of the disease, most dogs are asymptomatic. Because there usually are no signs of early disease and given the severity of advanced heartworm disease, annual heartworm testing and regular use of heartworm preventatives is the key to battling this parasite. Yearly testing for heartworm exposure is recommended at your pet’s annual preventative care examination and requires only a small blood sample.
If your dog tests positive for heartworm disease, treatment is required because the disease is fatal if left untreated. The goals of treatment are to stabilize your dog if he or she is showing signs of disease and then to kill all of the heartworms while attempting to minimize side effects. During treatment, strict exercise restriction is required which can be very challenging with an active, young dog but is a must to minimize organ damage and maximize the long-term health of your beloved pet. Treatment of affected dogs involves a series of injections and is very expensive and often quite painful.
Heartworm disease in cats is very different than in dogs. Because cats are not a standard host for heartworms, most of the worms will not survive to the adult stage. Many cats with heartworm disease have one or no adult worms. Even in the absence of adult worms, immature heartworms can still cause major, life-threatening damage to your furry friend. Symptoms of heartworm disease in cats are incredibly variable and unpredictable, ranging from extremely mild to acute collapse or even sudden death. There is no approved treatment protocol for heartworm disease in cats, so you will have to work closely with your veterinarian to create a plan for long-term management.
Prevention is, without a doubt, the best way to protect your pet. There are a variety of safe and effective heartworm preventative options, including pills, spot-on topical medications and even an injection. All approved heartworm preventatives work by eliminating the immature stages of the parasite before they have a chance to grow into an adult heartworm. Adult heartworms are not effectively eliminated by preventatives so it is essential to maintain a strict schedule of preventative administration. Oral and topical preventatives must be administered monthly and the injectable preventative is administered every 6 months by your veterinarian. Puppies and kittens should be started on heartworm prevention no later than 8 weeks of age. Discuss the best preventative options for your pet with your veterinarian.
For more details on heartworm disease and your pets, contact your veterinarian or visit the American Heartworm Society website.
By: Kerry Ryan, DVM