The Top 5 Myths About Heartworms
There are so many myths, misconceptions, and misunderstandings concerning heartworms, it is difficult to pick the top five. But if David Letterman can come up with a top 10 list every night on a myriad of topics, surely I can come up with five myths about heartworm disease. So here are my top five picks, counted down.
5. IT’S SEASONAL.
There is some small truth to this myth because heartworm transmission is dependent on climatic factors. It is widely accepted that a temperature of 57°F or higher is needed for heartworm larvae to develop to the infective stage within mosquitoes. With this information, ideally it should be possible to predict the transmission season in a given area. There are, however, two complicating factors: cyclic temperature variations due to weather patterns and changes from one environment to the next within local areas.
We all understand “mild” winters versus “cold” winters, but these local environmental changes are far more complex than that. The best way I can explain this is to give an example. Have you noticed when the weatherman reports the low temperatures on the evening news how the temperature varies in a downtown area versus in an outlying region? This is because roads, buildings, and other structures retain heat that is dissipated during the night, warming the air; thus, the more pavement, the larger the temperature variation. Water can have a similar effect on temperatures. As our communities grow, our average low temperatures rise a few degrees, which affects the length of the heartworm-transmission season.
As a result of this uncertainty, the American Heartworm Society (AHS) and the Companion Animal Parasite Council (CAPC) recommend year-round broad-spectrum heartworm prevention in all areas of the country. With year-round administration, you don’t have to remember when to start and stop giving your pet his medication. Plus, you gain the added benefit of controlling intestinal parasites year round (this is the “broad-spectrum” part). These parasites do not follow any “season,” and many of them are zoonotic, which means they can be transmitted to people. Not only do they infect three to six million people every year, but human intestinal parasite infections can lead to serious health problems.
"Year-round preventives help keep you and your family safe from zoonotic parasites—parasites that can be passed from pets to people."
4. IT’S REGIONAL.
This is another myth that has some basis in reality. Yes, the severity of infections is somewhat regional; for instance, an animal living in Louisiana is likely to harbor more worms than an animal living in Montana. Therefore, the recommendations for treating a heartworm-positive pet will vary based on the severity of the infection. However, the prevention recommendations remain the same across the country. This is because no heartworms or intestinal parasites are acceptable, so year-round administration of broad-spectrum heartworm prevention is the AHS and CAPC recommendation in all 50 states.
Heartworms have been diagnosed in all 50 states, and the number of new cases every year continues to go up, despite the highly effective heartworm preventives on the market.
3. IT’S HARD TO PROTECT AGAINST.
If you are concerned that giving your pet a pill or applying a topical medication once a month is too difficult a task, just think about everything you do for your pet every day (e.g., giving him food and water, exercising him). Although I have never had anybody tell me it’s too difficult, I have had numerous people tell me they just can’t remember to do it.
This is a common problem, but most people can find a way to remind themselves to administer heartworm preventives. My wife lives by her calendar, and she gives our dogs their pills on the first of every month. I have had several clients tell me they keep their pets’ pills with their car, rent, or mortgage coupon book and administer the medication on the day they pay that bill. Most heartworm pills come with stickers that you can place on your calendar.
Another common excuse I hear frequently is that heartworm preventives are too expensive. You can protect your small dog for 10¢ a day, and my Labrador retriever only costs 25¢ a day. Keep in mind that you can buy a lifetime of heartworm preventives for less than the cost to treat your pet for heartworms, not to mention it is better for the pet than having to suffer from the disease and subsequent treatment.
"Heartworm preventives protect your pet against nonseasonal intestinal parasites, too!"
2. IT’S EASY TO TREAT.
An average heartworm infection consists of a dozen or so worms that range from 6 to 14 inches in length and are located in the large artery that carries blood to the lungs and the heart. More severe infections can consist of 50 to 100 worms! There is no easy way to treat these infections. All treatments are designed to kill the worms, which then decompose, break up, and lodge in the capillaries (smallest blood vessels) of the lungs, where they obstruct blood flow. Here, specialized cells in the bloodstream help clear the dead worm particles. If the dog is allowed to exercise during the treatment period, the increased blood flow through the lungs associated with exercise can cause capillaries to rupture.
Treatments must be customized to the needs of each pet. Age, clinical signs, activity level, and major organ function have to be considered when formulating a treatment plan. Some cases can take 5 months or more to successfully treat; however, 95% of heartworm cases can be successfully treated. Although treatments can be difficult on a pet, a heartworm infection left untreated is even worse.
1. IT ONLY AFFECTS DOGS.
More than 30 species of animals are susceptible to heartworms: coyotes, foxes, wolves, and other wild dogs; domestic dogs; domestic and wild cats; ferrets; sea lions; and even people. There has even been one report of heartworm infection in a bird. However, heartworm disease is most misunderstood in the cat.
Even though heartworm disease in dogs is a cardiovascular disease that can lead to heart failure, heartworms primarily cause respiratory disease in cats. In addition, most heartworms in cats never make it to the adult stage. As a result of these two factors, feline heartworm infection is very hard to diagnose. There are many veterinarians who do not think it even exists. I, too, once was a skeptic.
When pharmaceutical companies first started marketing heartworm preventives for cats, I failed to see the need because I was rarely diagnosing heartworm infections in cats. Clients kept asking me about the incidence of heartworms in cats in our area, but I could not find any published studies. So I began examining cats in the area. The first week, I examined eight cats and found an adult heartworm in three! That got my attention. After examining cats over a 1-year period, my colleagues and I found that 10% had adult heartworm infections. This rate was sig- nificantly higher than that of local feline leukemia virus (FeLV) infection at 5% and feline immunodeficiency virus (FIV) infection at 6%.
In other studies, it has been shown that even though most heartworm larvae a cat receives from a mosquito bite never make it to the adult stage, inflammation is occurring in the lung tissue and is often misdiagnosed as asthma or allergic bronchitis.
What we’ve determined from all this is that cats need to be on a heartworm preventive, even if they are indoor cats. Mosquitoes do come inside. In a study conducted at North Carolina State University, 28% of the cats diagnosed with heartworms were considered to be “indoor-only” cats by their owners.
How Often Should I Have My Dog Tested?
Annual testing for heartworm infection is now highly recommended. Even though heartworm preventives, particularly monthly oral and topical formulations, are essentially 100% effective in preventing infection when administered according to instructions on the label, animals on heartworm prevention occasionally test positive for heartworms. This apparent lack of efficacy is usually due to owner compliance failure, travel or relocation of the animal to an area of active heartworm transmission, or unknown (or misdiagnosed) prior infection. Annual testing gives you peace of mind in knowing that your pet is free of heartworms, and if your pet is infected, it assures you of early diagnosis and maximum benefits from treatment.
TO LEARN MORE
Visit the American Heartworm Society’s website at www.heartwormsociety.org. The mission of the AHS is to further scientific progress in the study of heartworm disease and to encourage and promote effective procedures for heartworm diagnosis, treatment, and prevention, in order to contribute to a better understanding of this debilitating disease.