TERRI JOHNSON, AAHA PRACTICE ACCREDITATION
Heartworms—can you imagine actually having worms in your heart? Not a pleasant thought, but that’s exactly where they are.
The technical term for heartworm disease is dirofilariasis. Your veterinarian is checking for the presence of an antigen that would be in your dog’s bloodstream as a result of this disease when he/she does a yearly heartworm blood test.
Heartworm disease is one of the major health problems affecting dogs in the United States, and it is now being found in cats. The disease develops when a pet becomes infected with parasites transmitted through the bite of an infected mosquito. Dogs may be infected by a few or up to several hundred heartworms. Cats are similarly infected, although usually by only a few worms.
Having heartworm disease can lead to other medical problems beyond the heart, including lung, kidney and liver disease. The worms are found in the right side of the heart and in the major vessels that bring blood to and from the right chambers of the heart. The worms cause inflammation of the blood vessels and block blood flow. This can lead to pulmonary thrombosis (clots in the lungs) and heart failure. If left untreated, heartworm disease can result in liver and/or kidney failure. And heartworm disease can result in death due to one or a combination of these problems.
AAHA-accredited practices take a team approach to your pet’s health, and providing important tests to determine and prevent diseases is just one of the things they do to help your pet be healthy. It’s easier, better for your pet and less expensive to prevent diseases than it is to treat them.
Heartworm is a preventable disease for both dogs and cats but, prevention begins with you. With the right tests and preventive medications, your AAHA-accredited health care team can work with you to prevent many kinds of parasites. The practice staff members have access to a full array of appropriate tests to help prevent diseases and parasites from affecting your pet’s health.
Heartworm disease is evident in species other than dogs and cats. Ferrets can also be infected. Pets that spend a lot of time outdoors are at a greater risk for infection, especially in areas with a lot of mosquitoes. But even indoor pets can become infected by heartworms because infected mosquitoes can get inside your home. While heartworm disease primarily used to be a problem in the south and humid regions of the United States, it’s now found throughout the country.
If you travel with your pets, you may go into areas where there’s an increased risk of infection. Preventive medications are really important because heartworms breed in unprotected animals. Dogs that are not on heartworm preventive medications and certain wildlife, such as coyotes, wolves and foxes, can be carriers of heartworms.
The best way for easy, safe prevention of heartworm infection is to administer a year-round heartworm preventive prescribed by your veterinarian.
The American Heartworm Society and the Companion Animal Parasite Council recommend that all pets receive year-round heartworm protection so that pets are protected every month. It is critical that doses not be skipped or intervals between doses be extended because this results in an unprotected time during which animals may be exposed to heartworm larvae. Pets should also have annual heartworm testing by a veterinarian prior to prescribing a heartworm medication.
Adult female heartworms can live in an infected dog or other hosts and release their young, called microfilaria, into the bloodstream of that host. Mosquitoes are infected by the microfilaria when they bite an infected animal. In 10 to 14 days, the microfilaria mature to the infective larval stage within the mosquito. When the mosquito bites another dog, cat or susceptible animal, the infective larvae exit the mosquito’s mouth and are deposited onto the surface of the animal’s skin. The infective larvae can then enter the new host through the fresh bite wound.
It takes about 6 months for the infective larvae to mature into adult heartworms in the new host. Mature, heartworms can live 5 to 7 years. Because they live so long, each mosquito season has the potential of an increasing number of infestations and increased infections in our pets.
Per guidelines from the American Heartworm Society, all dogs should be tested for heartworms annually and before starting a preventive program. Giving preventives to dogs that already have adult heartworm infection can be harmful or even fatal because adult heartworms produce millions of microscopic “baby” heartworms in the bloodstream.
Giving a monthly heartworm preventive to a dog with circulating microfilaria could cause the sudden death of the microfilaria, triggering a shock-type reaction. Even if your dog does not have this type of reaction, heartworm preventives do not kill the adult heartworms (although they may shorten the worms’ lives). This means an infected dog will remain infected with adult heartworms.
So both adult and baby heartworms must be eradicated to actually cure a dog. As long as the dog remains infected, heartworm disease will progress and damage organs, increasing the possibility of life-threatening problems. Giving heartworm preventives to heartworm-positive dogs can mislead you into thinking that everything is all right, while the heartworm disease is actually worsening.
Heartworm disease is more challenging to detect in cats than in dogs. The preferred method for screening cats includes both an antigen and an antibody test. Cats should be tested prior to starting a preventive program and then annually thereafter. There is no approved treatment for heartworm infection in cats, so prevention is very important.
Early detection and treatment are always best. With annual testing, you’ll know your pet is heartworm-free.
Heartworm Life Cycle used with permission from the American Heartworm Society. For more information, please visit www.heartwormsociety.org.
Revised and updated Dec. 18, 2012.
This article originally appeared in PetsMatter July / August 2012, published by the American Animal Hospital Association. Copyright © 2012 AAHA. Find out more.