Heartworm Awareness & Prevention: What Pet Parents Need to Know

April is Heartworm Disease Awareness and Prevention Month. In many North American regions April is the time of the year when veterinarians begin to check dogs and cats for exposure to heartworm organisms that may have occurred during the previous mosquito season. Heartworm disease is a serious and potentially fatal disease in pets in the United States and many other parts of the world. In fact, the American Heartworm Society reports that more than one million dogs currently have heartworm disease. They also report that heartworm is a serious canine and feline health concern that threatens animals in all 48 contiguous states and Hawaii, as well as throughout the temperate regions of the world.

What is Heartworm Disease?

Heartworm is a preventable, but serious and potentially fatal, parasite that primarily infects dogs, cats and ferrets. It can also infect a variety of wild animals, including wild foxes, wolves, coyotes, raccoons and opossums, as well as others. There have been documented human infections, but they are thought to be rare and do not usually result in signs of illness.

 How is Heartworm Disease Transmitted?

Only by the bite of an infected mosquito. There’s no other way your pet can get heartworms. And there’s no way to tell if a mosquito is infected. That’s why prevention is so important. Heartworm disease has been reported in all 50 states. And the bite of just one mosquito infected with the heartworm larvae will give your pet heartworm disease. It takes about seven months, once your pet is bitten by an infected mosquito, for the larvae to mature into adult heartworms. They then lodge in the heart, lungs, and surrounding blood vessels and begin reproducing. Adult worms can grow up to 12 inches in length, can live 5-7 years in a dog and several months to a year in a cat. Heartworm Disease in dogs and cats has its differences though: Dogs The dog is a 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 and quality of life long after the parasites are gone. For this reason, prevention is by far the best option, and treatment—when needed—should be administered as early in the course of the disease as possible. Cats 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. While this means heartworm disease often goes undiagnosed in cats, it’s important to understand that even immature worms cause real damage in the form of a condition known as heartworm associated respiratory disease (HARD). Moreover, the medication used to treat heartworm infections in dogs cannot be used in cats, so prevention is the only means of protecting cats from the effects of heartworm disease.

How do I know if my pet has been infected?

Dogs If your dog has been recently or mildly infected with heartworms, he/she may show no signs of illness until the adult worms have developed in the lungs and signs of heartworm disease are observed. As the disease progresses, your dog may cough, become lethargic, lose his/her appetite or have difficulty breathing. You may notice that your dog seems to tire rapidly after only moderate exercise. Blood tests are performed by your veterinarian to detect the presence of adult heartworm infection (> 6 month old infections) in your dog. Antigen tests detect the presence of adult female heartworms, and antibody tests determine if your pet has been exposed to heartworms. The antigen test is most commonly performed, and is very accurate in dogs. Further tests, such as chest radiographs (x-rays), a blood profile and an echocardiogram (an ultrasound of the heart), may be necessary to confirm the diagnosis, to evaluate the severity of the disease, and to determine the best treatment plan for your dog. Cats Signs of possible heartworm disease in cats include coughing, respiratory distress, and vomiting. In some cases, a cat may suddenly die from heartworms. The diagnosis of heartworm infection in cats is more difficult than it is with dogs. A series of different tests may be needed to help determine the likelihood of heartworm infection as the cause of your cat's illness and, even then, the results may not be conclusive. In general, both antigen and antibody tests are recommended for cats to give the best chances of detecting the presence of heartworms.

Is There Treatment?

Dogs Melarsomine dihydrochloride (available under the trade names Immiticide and Diroban) is an arsenic-containing drug that is FDA-approved to kill adult heartworms in dogs. It's given by deep injection into the back muscles to treat dogs with stabilized class 1, 2, and 3 heartworm disease. Another drug, Advantage Multi for Dogs (imidacloprid and moxidectin), is FDA-approved to get rid of microfilariae in the dog’s bloodstream. Advantage Multi for Dogs is a topical solution applied to the dog’s skin. The treatment for heartworm disease is not easy on the dog or on the owner’s pocket book.  Treatment can be potentially toxic to the dog’s body and can cause serious complications, such as life-threatening blood clots to the dog’s lungs.  Treatment is expensive because it requires multiple visits to the veterinarian, bloodwork, x-rays, hospitalization, and a series of injections. Cats There is no FDA-approved drug to treat heartworm disease in cats, although symptoms may be managed with medications.  Surgical removal of adult heartworms may be a treatment option if the heartworms can be seen by ultrasound.  But surgery is risky, and if the heartworms are not removed intact, there can be potentially serious complications, such as shock and death.

The Best Treatment is PREVENTION!

Types of Heartworm Preventives Listed on FDA.gov A variety of products are available by prescription only:

  • oral pill or tablet - ivermectin - milbemycin oxime
  • topical liquid that the owner squeezes from a tube onto the pet's back - selamectin - moxidectin
  • injectable (for dogs only) - moxidectin

A few heartworm preventives are combined with other ingredients to kill fleas and some types of ticks and intestinal parasites. Because pets that have heartworms may not show symptoms right away, your veterinarian may test your pet before prescribing heartworm preventive, and then yearly, to make sure the pet is not infected. Dogs are tested for heartworm using simple blood tests. Testing in cats, however, is more difficult than, and not as accurate as, testing in dogs. Injectable Heartworm Preventive ProHeart 6 (moxidectin) Sustained Release Injectable for Dogs is the only six-month injectable heartworm preventive approved in the United States. First approved in 2001, ProHeart 6 was voluntarily recalled by the original manufacturer, Fort Dodge Animal Health, in 2004 based on FDA's concerns regarding reports of serious side effects, including death. In June 2008, FDA concurred with Fort Dodge's decision to reintroduce ProHeart 6 to the U.S. market under a special program to manage the risks and restrict distribution. After the recall, Fort Dodge

  • revised the product label and Client Information Sheet to include updated safety information
  • revised the risk minimization and restricted distribution program several times to reflect current safety information

ProHeart 6 is the first veterinary drug ever sold under a risk minimization and restricted distribution program similar to that used successfully for some human drugs. Now manufactured by Zoetis, ProHeart 6 continues to be sold under the program which requires the following procedures:

  • Veterinarians need to register with the manufacturer and complete in-depth training prior to purchasing ProHeart 6.
  • Only veterinarians and staff who have completed the training can inject the drug into the dog.
  • Veterinarians need to provide clients with an information sheet about the drug's risks.
  • Veterinarians need to record the product lot number in the medical record and report any unexpected side effects.

FDA.gov Tips for Consumers

  • Ask your veterinarian if your dog or cat should be on a heartworm preventive.
  • Store all medications away from children and pets. Your dog may not distinguish a chewable heartworm preventive drug from a tasty treat.
  • You can buy heartworm preventive from your veterinarian. If you buy it from an Internet pharmacy, follow the advice in Purchasing Pet Drugs Online: Buyer Beware.
  • If you think your pet is having a side effect from a heartworm preventive, call your veterinarian immediately. In addition to treating your pet, your veterinarian can notify the manufacturer, who is required to report side effects to FDA. Owners can also file a report directly with CVM if they wish.

What About Natural Alternatives for Heartworm Prevention?

Heartworm preventives are highly effective, but they are not without risks. Adverse effects of heartworm preventions include milder reactions such as vomiting and loss of appetite, but also more serious problems, such as shock, tremors, coma, seizures, and respiratory failure, explains holistic veterinarian Judy Morgan, DVM, author of From Needles to Natural: Learning Holistic Pet Healing and a certified pet acupuncturist and food therapist. This may have you looking for a more natural way to protect your pet. There are a natural products such as our Ultimate Outdoor Protection and our Flea & Tick Spray for Dogs with safe ingredients that can help to “repel” pests (mosquitoes), and should always be used when your pet is outside to avoid bites, unfortunately their effectiveness to actually prevent infection is chancy. In fact, Dr. Morgan points out that while she's an avid supporter of holistic medicine and homeopathy, and believes while natural heartworm preventives may be very helpful in the fight against heartworm disease, they are definitely not guaranteed to be 100% effective. If the idea of using heartworm preventives still makes you wary, Dr. Morgan says one solution is to consider the actual risk of heartworm infestation in particular regions of the country. Mosquitoes are basically active, and heartworm larvae within the mosquitoes can mature, when the ambient temperature remains over 57 degrees around the clock for two weeks straight.