Heartworm disease is a serious and potentially fatal disease in pets. It’s caused by worms (adults can reach as big as a foot in length) that live in the heart, lungs and associated blood vessels of affected pets causing sever lung disease, heart failure, and can result in damage to other organs in the body. Heartworm disease affects dogs, cats, and ferrets. We have heard of these worms in pets- but did you know heartworms also live in many other species of mammals including wolves, coyotes, foxes, sea lions and in rare instances, humans!
Dogs- dogs are the natural host for heartworms, which means that heartworms that live inside the dog mature into adults, mate and produce offspring. If untreated, their numbers can increase, and dogs have been known to harbor several hundred worms in their bodies. Heartworm disease causes lasting damage to the heart, lungs and arteries, and can affect the dog’s health long after the parasites are gone. Cats- Heartworm disease in cats id very different from dogs. The cat is an atypical host for heartworms, and most worms in cats do not survive to the adult stage. Cats with adult heartworms typically have just one to three worms, and many cats affected by heartworms have no adult worms. Its important to know that even immature worms can cause real damage, and heartworm medication for dogs cannot be used for cats. So, prevention is the only means of protecting cats from these worms.
The Role of The Mosquito:
Mosquitoes play an essential role in the heartworm life cycle. Adult female worms living in an infected dog, coyote, wolf or other animal produce microscopic baby worms called microfilaria. They circulate in the bloodstream. When a mosquito bites and feeds from an infected animal, it picks up the microfilaria, which then develop and mature into “infective stage” larvae over a period of 10-14 days. Then the mosquito bites into another animal, and the infective larvae are deposited onto the surface of the animal’s skin and enter through the mosquito bite wound. Once inside the new host, it takes approximately 6 months for the larvae to mature into adult heartworms. Once mature, heartworms can live 5-7 years in dogs and up to 2-3 years in cats. Because of the longevity of these worms, each mosquito season can lead to an increasing number of worms in an infected pet.
Signs & Symptoms:
In the early stages of the disease, many dogs show few or no symptoms at all. The longer the infection persists, the more likely symptoms will develop. Active dogs, dogs heavily infected with heartworms, or those with health problems often show pronounced clinical signs. Signs of heartworm disease may include a mild persistent cough, reluctance to exercise, fatigue after moderate activity, decreased appetite, and weight loss. As heartworm disease progresses, pets may develop heart failure and the appearance of a swollen belly due to excess fluid in the abdomen. Dogs with large numbers of heartworms can develop sudden blockages of flow within the heart leading to a life-threatening form of cardiovascular collapse. This is called caval syndrome and is marked by a sudden onset of labored breathing, pale gums, and dark bloody or coffee colored urine. Without prompt surgical removal of the heartworm blockage, few dogs can survive.
Why Testing is Important:
Because this disease is so progressive and potentially fatal, testing should be done routinely. Puppies under 7 months of age can be started on heartworm prevention without a heartworm test, but should be tested 6 months after your initial visit, tested again 6 months later, and yearly after that. Adult dogs over 7 months of age and previously not on preventative treatment need to be tested prior to starting heartworm prevention. They too need to be tested 6 months and 12 months later and annually after that. If there is a lapse in prevention, dogs should be tested immediately, then tested again 6 moths later and annually after that.
Because we can’t see them, and its impossible to know when your dog gets each mosquito bite, regular testing is imperative. This includes all pets, even those indoors since mosquitos can sometimes get inside. If your pet starts showing symptoms, contact your vet right away. This disease is fast moving, but treatable, and more importantly preventable.