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Heartworm disease is a parasite that colonizes and gradually destroys the heart, pulmonary artery, and lungs. It is transmitted via the bite of a mosquito infected with microfilaria (a microscopic baby heartworm) as it injects the larvae into the dog’s blood stream when feeding on a dog. Heartworm can also infect wild species of canids, such as foxes, coyotes, and wolves. Less commonly, heartworm can infect cats, ferrets, and raccoons
As an integrative veterinary practitioner, a branch of medicine that combines traditional western veterinary medicine with proven, natural, side effect free veterinary medicine alternatives, I frequently get asked if there are any natural options for preventing heartworm disease in dogs. My answer is yes, but it is not likely the answer that a natural medicine or holistically minded person may expect.
The three most active ingredients in commercial monthly heartworm preventive medications – ivermectin, milbemycin oxime, and selamectin – are all derived from a compound within the naturally occurring soil bacteria Streptomyces avermitilis. It was observed by the Kitasato Institute that certain soils were toxic to several species of invertebrate animals, an animal classification that includes many species of worms. In 1979, a unique bacteria was isolated by the Kitasato Institute that they believed was responsible for the inability of certain worms to survive in the soil.
The Institute sent the bacterial isolate to Merck Sharp & Dohme Research Laboratories in Rahway, NJ, where it was discovered that it was a particular class of compound called avermectin secreted by the bacteria that was responsible for its ability to kill worms. It was theorized that the secretion of this compound evolved as either a mechanism to kill soil worms to be used by the bacteria as a food resource or to eliminate the worms which are competition for soil nutrients.
Whatever the case may be, this discovery would soon take human and veterinary parasite medicine by storm. It began with the recognition that one of the avermectin derivative compounds, ivermectin, was effective in treating Onchocerca volvulus, the worm parasite responsible for causing River Blindess, a disease that is spread by the bite of the black fly and infects 16 million people a year world wide. The disease is seen most commonly in sub-Saharan Africa and isolated areas of Central and South America.
As the worm larvae develop, they migrate to the skin cause a severe itch, with some cases tormenting infected victims to the extent that there have been many reports of people resorting to burning affected area of the skin with hot coals or hot irons as desperate attempts to relieve the itch. The can larvae travel to the eyes and also cause blindness, hence the name of the disease (the “River” part come from the fact that black flies live near river banks). Significant to complete blindness from Onchocerca volvulus is reported in approximately 800,000 people world wide each year. With the advent of ivermectin and its commercial production by Merck, millions of people each year are spared the tormenting and potentially tragic consequences of infection with Onchocerca volvulus.
Ivermectin and other derivatives of avermectin have proven to treat countless worm and other parasites in both human and veterinary medicine. Perhaps the biggest contribution of the discovery of avermectins in veterinary medicine is the prevention of heartworm disease, which is nearly 100% preventable with monthly micro-doses of these compounds available in any number of commercial products. Not only are these products naturally derived, while they may be quite toxic to immature worms, they are virtually harmless to mammalian vertebrates, the class of animals that includes dogs and people.
So there you have it, safe and natural heartworm prevention has existed for decades and is available at just about every veterinary clinic in the United States. This is probably not what a holistically or naturally minded pet owner expected to or even wanted to read, but it is the truth. Instead, it is more likely that a reader that was excited to finally have a veterinarian show concrete evidence of one of the common natural heartworm preventive herbal and other concoctions touted or sold online, actually works. I am sorry to disappoint, but these alternative treatments are at best doubtful, at worst toxic. Lets review some of the more common ones.
Garlic: Believed by some to stop the maturation of heartworms – Ineffective and toxic to dogs.
Sorrel: Claimed to clear the blood stream of worms, serving as cardiovascular detox – complete and utter rubbish and toxic toxic to dogs.
Guinness Beer: No comment, I will just leave this one for you to contemplate!
Black Walnut Hull: Claimed to kill the microfilaria (infective heartworm larvae injected by the infected feeding mosquito) before it can mature to juvenile and adult stages – Anecdotal reports of efficacy only, luckily not likely to be toxic.
Essential Oils: Claim to prevent heartworm by repelling the pests from feeding on the pet in the first place – Ineffective and possibly tormenting for the pet (essential oils tend to have a very strong scent to us, imagine how they would smell to a dog that can smell 200,000-300,000 more acutely than we can?).
In a heartworm prone area (anywhere mosquitoes exist and the temperature can remain above 57 degree F for two weeks or longer at any given time) I would not recommend risking heartworm infection or possibly intoxicating your dog with any of these and other supposed natural heartworm preventives, especially when proven, naturally derived heartworm prevention already exists; albeit, not necessarily fitting within certain holistic pet owners’ narrative.
Dr. Roger Welton is a practicing veterinarian and highly regarded media personality through a number of topics and platforms. In addition to being passionate about integrative veterinary medicine for which he is a nationally renowned expert, Dr. Welton was also an accomplished college lacrosse player and remains to this day very involved in the sport. He is president of Maybeck Animal Hospital , runs the successful veterinary/animal health blogs Web-DVM and Dr. Roger’s Holistic Veterinary Care, and fulfills his passion for lacrosse through his lacrosse and sport blog, The Creator’s Game.