The Problems With Heartworm Preventives — They Don't Prevent Anything

heartworm prevention

Story at-a-glance -

  • April is National Heartworm Awareness Month, but unlike the conventional veterinary community, I don’t agree with the recommendation to give every pet everywhere a heartworm preventive every month of the year
  • It’s important to assess your pet’s actual risk of acquiring heartworms based on where you live and your lifestyle
  • If you live in a mosquito-endemic area, it’s also important to know the best months to start and stop administering heartworm preventives to your pet, and use chemical heartworm preventives at the lowest effective dosage and follow up with natural liver detox agents
  • Steps to help prevent heartworm disease in your pet include trying natural preventives with follow-up testing as appropriate, and keeping your pet’s immune system in excellent condition
  • Most importantly, have your pet tested for heartworms and other parasitic diseases at the beginning and again at the end of pest season

By Dr. Karen Shaw Becker

April is National Heartworm Awareness Month, so if you happen to have an appointment with your conventional veterinarian in the next few weeks, you should probably anticipate a sales pitch for chemical heartworm preventives. That's because the American Heartworm Society recommends you give your pet heartworm preventive 12 months a year, no matter where you live or your pet's risk of exposure.

Needless to say, I absolutely do not agree that every pet, everywhere, should be given a chemical insecticide once a month, year in and year out (I'll offer my recommendations shortly). No drug is entirely harmless. Heartworm preventives are chemical insecticides with the potential for short- and long-term side effects that can damage your pet's health.

Many pet parents don't realize these preventives don't actually prevent anything. They poison heartworm larvae at the microfilaria stage of development, causing them to die inside your pet's body. And in addition to concerns about the toxicity of these insecticides, there's also evidence heartworms are growing resistant to them.

First Assess Your Pet's Individual Risk of Acquiring Heartworms

The rationale for recommending year-round heartworm preventives to all pets everywhere is that, according to the American Heartworm Society, heartworm disease has been diagnosed in all 50 states, and risk factors are impossible to predict.

However, while it may be true that at least 1 dog in all 50 states has been affected, it doesn't mean heartworm disease is a significant threat in every state, or even in most states. And it's true that climate variations and the presence of wildlife disease carriers can be unpredictable, but a change in one or two risk factors doesn't increase the exposure risk across the board.

According to the most recent heartworm prevalence map published by the Companion Animal Parasite Council (CAPC), 1 out of every 70 dogs in the U.S. — less than 1.5 percent — will test positive for heartworm. And despite the fact that cats aren't natural hosts for heartworm, year-round preventives are now being recommended for them as well.

There are only 14 states in which dogs are considered at high risk for heartworm infection — a situation that has remained essentially unchanged for years. Those states are primarily in the southeast, where high temps and humidity during the warmer months of the year provide an ideal environment for mosquitoes to thrive.

You can use the heartworm prevalence map linked above to drill down to not only your state, but also your county to get information about the prevalence of heartworm disease (as well as other parasitic diseases) in your area.

The Best Times to Start and Stop Preventives in Mosquito Endemic Areas

There are only a few areas in the U.S. in which giving a year-round heartworm preventive might be advisable — those areas are in south Texas, south Florida and a few other locations along the Gulf Coast. The rest of the U.S. ranges from three to seven months of high exposure risk. The majority of states are at six months or less.

If you're concerned your dog is at risk of a heartworm infection, in consultation with your holistic or integrative veterinarian, you can use the following maps to guide you in when to start and stop a heartworm preventive.

first monthly dose heartworm preventive
Timing of First Monthly Dose of Heartworm Preventive

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last monthly dose heartworm preventive
Timing of Last Monthly Dose of Heartworm Preventive

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6 Recommendations to Help Your Pet Avoid Heartworm Disease

If you live in an area of the U.S. where mosquitoes are common and you know your dog's risk of exposure to heartworm disease is significant, here are my recommendations for protecting your furry family member:

If you don't live in a tick-endemic area (for example, if you live in North Dakota), with guidance from a holistic or integrative veterinarian, try using natural preventives like heartworm nosodes rather than chemicals. Make sure to do heartworm testing every three to four months (not annually), as natural heartworm preventives can't guarantee your pet will never acquire the disease.

It's important to note that since heartworms live in the bloodstream, natural GI (gastrointestinal) dewormers such as diatomaceous earth, and anti-parasitic herbs (e.g., wormwood, pumpkin seed, black walnut tinctures) are not effective at killing larvae in the bloodstream.

Focus on keeping your pet's immune function robust by feeding a species-appropriate, nutritionally balanced, fresh food diet that helps bolster natural defenses. Unprocessed meats are rich in B vitamins (and a less allergenic option than offering brewer's yeast). Also, specific anti-parasitic foods such as fresh garlic can be added in small quantities to provide additional anti-parasitic support.

If your dog's kidneys and liver are healthy, try using a chemical preventive at the lowest effective dosage. This could mean having the Ivermectin compounded if necessary for dogs weighing in at the low end of dosing instructions. Give the treatment at six-week intervals rather than every four weeks, for the minimum number of months required during mosquito season.

Avoid all-in-one chemical products that claim to get rid of multiple types of GI worms and external parasites as well. The goal is to use the least amount of chemical necessary that successfully treats heartworm. Adding other chemicals to the mix increases the toxic load your dog's body must contend with. Also avoid giving your pet a chemical flea/tick preventive during the same week.

Follow up all heartworm medications with natural liver detox agents like milk thistle and SAMe for a week following chemical treatment, in consultation with your veterinarian.

Always insist on a heartworm test before beginning any preventive treatment. If you live or spend time with your pet in areas where mosquitoes and other pests, especially ticks, are prevalent, ask your veterinarian for a SNAP-4Dx test or an Accuplex test, both of which check for Lyme disease, ehrlichiosis and anaplasmosis, along with heartworm.

I like to run the SNAP 4Dx blood test I mentioned earlier every six months on dogs who spend a lot of time outdoors during warmer weather. The reason I do tests every six months is because parasites are becoming resistant to heartworm and flea/tick chemicals. The sooner we identify an infection in your pet, the sooner a protocol can be instituted to safely treat it with fewer long-term side effects.

If you live in the midwest or the east coast of the U.S., it's a good idea early in the year and at the end of pest season to check for these illnesses, which can be resistant to preventives and are relatively easy to treat and cure when they're identified before they create chronic disease.

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