With the approach of the warmer weather, comes the dreaded increase in the population of mosquitoes. Mosquitoes pose a very dangerous threat to our pets; they transmit heartworm disease. Heartworm disease affects over 30 species of animals. According to the American Heartworm Society, dogs are the definitive host for heartworms (Dirofilaria immitis). Canine heartworm infections occur in dogs of all ages, breeds and sex, in all 50 states.

The geographical area that has the highest number of heartworm positive animals lies along the Atlantic and Gulf Coasts. Texas has one of the highest numbers of heartworm positive dogs in the United States! Despite improved diagnostic methods, effective preventives and increasing awareness among veterinary professionals and pet owners, cases of heartworm infection still continue to appear in our beloved pets. Why? Many do not understand heartworm disease.

What is heartworm disease? Heartworm disease is a serious and potentially fatal condition caused by parasitic worms living in the arteries of the lungs and in the right side of the heart of dogs, cats and other species of mammals. The transmission of heartworms begins with the mosquito ingesting the heartworm larvae while taking a blood meal from an infected animal. The mosquitoes then transmit the infection, in their saliva, to another animal during their subsequent meals. Once the larvae are deposited, they then travel through the animal’s bloodstream and tissues for several months (six to seven months) until they reach the heart and pulmonary blood vessels. During their migration they become sexually mature. Male heartworms are four to six inches in length and the females are ten to twelve inches long (resembling spaghetti noodles). Each adult heartworm can live five to seven years in a dog’s body. The adult worms reproduce and in doing so cause the animal’s heart to enlarge to accommodate the increasing number of worms. With time the changes to the animal’s heart are so severe and irreparable that the heart fails, leading to the animal’s death.

Although this infection is seen mainly in dogs, outdoor cats are at a great risk of becoming infected, and a relatively high percentage of cats considered by their owners to be indoor pets also become infected (Mosquitoes get in our homes too).

What is the cause of death, you may wonder; well heartworm disease may cause a combination of medical problems within the same dog including dysfunction of the lungs, heart, liver and kidneys. 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 (as mentioned above), where they cause inflammation and interfere with blood flow. This primarily causes pulmonary thromboembolisms (clots in the lungs) and congestive heart failure. It can also lead to liver or kidney failure. Death can be caused by one or a combination of these problems.

Prevention is always better then treatment! A simple blood test can be performed by your veterinarian to detect the presence of immature heartworms (microfilaria) in your pet. Tests are available for both dogs and cats and only take a few minutes and a few drops of blood to be completed. This is important as giving heartworm preventives to dogs having heartworms can lead to severe reactions that could be harmful or even fatal to the dog.

There is a window period of six to seven months where the test may reveal a false negative result. This represents the time period from when the larvae has entered the animal’s body until the microfilaria can be detected in the blood. There are extremely effective heartworm preventatives available that not only prevent heartworms, but certain intestinal parasites as well. There are combination drugs that even cover flea prevention or ear mite prevention. Compared to the alternatives, they are inexpensive, easy and safe. All products are administered once a month and are available for dogs, cats and ferrets. All products require a prescription by federal law and are available from your veterinarian. When administered properly and purchased from your veterinarian, heartworm prevention is guaranteed to prevent heartworm infection. There is no natural prevention for heartworms. Talk to your veterinarian to determine the best product for your beloved pet.

Written by: Erica Haley, DVM and Madelen Powell