As warmer weather approaches, so, inevitably, does the return of the mosquito. It is appropriate, then, that April is Heartworm Awareness Month.
Heartworm disease is a serious and potentially fatal disease caused by parasitic worms living in the pulmonary arteries and occasionally in the right side of the heart of dogs and cats. All dogs and cats are at risk for heartworms, and heartworm disease has been diagnosed in all 50 states.
Heartworms are spread by mosquitos. When a mosquito bites an infected dog, it picks up the heartworm larvae in the blood. It can then infect the next dog it bites with the infective larvae, which grow and migrate through its host’s body over the next few months until it is a mature adult.
Adult heartworms can reach lengths of up to 14 inches, and dogs with severe heartworm disease can harbor more than 50 worms! Initially the worms live in the arteries around the lungs, but once the worm burden increases, they back up into the right chambers of the heart where they can cause heart enlargement and congestive heart failure.
Dogs show no symptoms in the early stages of heartworm disease. As the disease progresses, you may notice a slight cough and exercise intolerance. In severe cases of heartworm disease, persistent coughing, weakness, trouble breathing and fainting can occur.
Your veterinarian can perform a blood test to determine if your dog is heartworm positive. This is generally done at your dog’s annual checkup. It’s worth noting that it takes about six months after infection for a heartworm test to show up positive, so if your pet was exposed last month the test will not be accurate.
If your dog is heartworm positive, your veterinarian will go over the treatment options. To determine what stage of heartworm disease your dog is in, your vet may take X-rays of your dog’s chest and perform additional blood work. Then a series of injections will be given over a month’s time that will slowly kill the adult worms. At the same time, your dog will be started on a product to kill the circulating microfilaria, or baby worms. The most serious and potentially fatal complication following this treatment is pulmonary thromboembolism from dead and dying worms.
Heartworm disease can be fatal, and the treatment also carries risks. But take heart--you can prevent heartworm infection by administering a monthly heartworm preventative such as Heartgard, Interceptor or Revolution. These medications are very effective at preventing heartworm infections.
What about cats?
Cats are also at risk for heartworm disease, though they are not the normal host. Heartworm disease is particularly frustrating in our feline friends because clinical signs often mimic other diseases. Often times, sudden death occurs without warning. Additionally, testing in cats can be confounding, and there is no approved treatment for heartworm disease in cats. Even if you consider your cat indoor only, you should be giving her heartworm prevention each month -- roughly 25% of heartworm positive cats are “indoor only.”