by Diana Bocco
If you're worried about what heartworm prevention drugs are doing to your dog, you're not alone. In fact, many pet owners are reconsidering the use of preventives and are in search of natural options.
But abandoning heartworm preventives can have serious consequences. Pet owners should work directly with their veterinarians to figure out the best options for their dogs.
Standard Preventives for Heartworm
Heartworms are parasites that reside in the heart and lungs of affected pets. Dogs are particularly susceptible to heartworm infection (which is transmitted from one animal to another through mosquito bites), but cats, ferrets, and some other species of mammals can also become infected. Left untreated, heartworm disease can cause severe damage to the heart, lungs, and other organs, and will often lead to death.
The heartworm preventives currently on the market are manufactured by pharmaceutical companies and are FDA approved. According to Tennessee-based Eva Evans, DVM, these drugs have proven efficacy against the microfilaria (larvae, or "baby worms") that are spread by mosquitos.
“The only effective medication on the market to kill the larvae before they become full grown adult worms is what is called a Macrocyclic Lactone,” Dr. Evans explains. “This drug class includes Ivermectin, Moxidecton, Milbemycin and Selamectin—the active ingredient in prescription heartworm preventatives.”
Risks and Problems With Heartworm Preventives
While heartworm preventives are highly effective, 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.
“Sadly, drug reactions to heartworm preventatives can be very serious and can include death,” according to Dr. Morgan. These types of reactions are almost always associated with overdoses of heartworm medications; for instance, when a dog finds a package of preventive medicine and eats a 12 month supply at one time.
That said, it’s important to keep in mind that any pet can have a reaction to any medication at any time.
“That means that your pet could have a reaction to antibiotics, joint supplements, new foods, anti-anxiety medications, and more,” explains Dr. Evans. “It is important to remember that reactions are extremely rare, and a majority of reactions are mild.”
Dr. Evans also points out that you need to think about the hundreds of thousands of pets who are getting heartworm prevention every month for life, not only in the United States, but in other countries as well.
“Only a tiny fraction of these pets ever have any problems,” Dr. Evans says. “Most adverse reactions are mild and limited to hives, facial swelling, vomiting, or diarrhea.”
What Happens If Your Dog Cannot Tolerate Chemical Preventives?
While drug reactions can happen in any pet, some breeds are particularly sensitive to certain drugs, according to Dr. Morgan.
“This is true, for instance, for the dogs that carry the MDR1 [also called ABCB1] gene mutation, also known as the 'white-footed gene' because many of the dogs with the mutation have white feet,” Dr. Morgan explains.
“This mutation of the 'multi-drug resistant' gene allows chemicals to build up to toxic levels in the brain, whereas normally the non-mutated gene would prevent neurotoxins from entering the brain.”
The most commonly affected “white-footed” breeds are herding dogs, such as Collies (all types), Australian Shepherds, Shetland Sheepdogs, Australian Cattle Dogs, and Corgis, although many other breeds and mixed breed dogs may carry the gene as well.
If you are worried about your dog carrying the gene, a quick blood sample or cheek swab can be taken by your veterinarian and used to test for the presence of the MDR1 mutation to determine whether your dog may have increased sensitivity to these drugs.
What happens if the results are positive? Evans says there's no reason to despair. “Even dogs with this genetic mutation can still take heartworm prevention safely; we just have to be careful not to give them overdoses,” Dr. Morgan says. The macrocyclic lactone dose in heartworm prevention is so tiny that it is safe for all breeds of dogs.
What About Natural Alternatives for Heartworm Prevention?
There are a number of heartworm preventatives advertised as being natural alternatives available on the market. Most of them are basically a combination of tinctures (liquid extracts), herbs, and, sometimes, essential oils, with some also containing diatomaceous earth and black walnut.
While some of these ingredients can help to “repel” pests (i.e., make your dog less attractive to mosquitoes), their effectiveness to actually prevent infection is, at best, doubtful. In fact, Dr. Morgan points out that while she's an avid supporter of holistic medicine and homeopathy, and believes natural heartworm preventives may be very helpful in the fight against heartworm disease, they are definitely not guaranteed to be 100% effective.
Dr. Evans adds that many products sold as natural preventives are actually downright dangerous. She cites the example of one “natural” option that contains garlic, sorrel, and grain alcohol—all toxic to dogs and cats. “Not only are these concoctions a waste of money, but you could cause direct harm by giving them to your pet,” Dr. Evans explains.
Another commonly recommended “natural solution” is to strengthen your pet's immune system so that, in theory, it can then fight the infection on its own. According to Dr. Evans, this too is poor advice.
“I will use this example on why strengthening your dog's immune system will not prevent heartworm infection: Perfectly healthy [human] travelers to malaria endemic regions still need to take anti-malarial pills! Being a healthy human does NOT prevent Malaria infection, and being a healthy dog or cat does NOT prevent heartworm infection.”
Weighing Your Options on Heartworm Prevention
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.
“Use of monthly year-round heartworm prevention makes no sense (to me anyway) in areas of the country that are blanketed in cold and snow half the year,” Dr. Morgan says. “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.”
In the end, though, Dr. Evans says the take home message is that “your pet is substantially more likely to contract and even die from heartworms than to have a reaction to the prevention.”