The most reliable way to protect your dog from heartworm disease is to administer a veterinarian-prescribed, FDA-approved heartworm preventative, at the recommended dose and interval, all year round. These medications, when administered at the recommended dosages, are safe for dogs of all breeds, including those with MDR1 mutations.
FDA has approved about a dozen drugs for prevention (see chart). The drugs used in all of these products are designed to kill developing heartworm larvae, as well as any other parasites. Which parasites will be killed by the drug depends on its formulation. These products can be given either orally or topically, or as subcutaneous injections by veterinarians at six-monthly or 12-monthly intervals. As long as they are administered as prescribed, you can protect your dog against heartworm infections. Use the drug that you can most reliably obtain and give to your dog according to schedule.
Consider using whichever medication also treats infestations of parasites in your area or on your dog. If fleas are a concern for your dog then using a product to prevent heartworms that also kills the tapeworms transmitted by infected fleas is a great idea. Drugs that treat these infections are beneficial for dogs who were rescued from shelters or hoarding situations.
Heartworm Life Cycle & How Preventatives work
Heartworms in adult dogs can be the most dangerous of all the round worms (nematodes) that affect dogs. They can cause severe illness and even death, if they are not treated.
Mosquitoes spread heartworms. When a mosquito bites a dog infected with heartworms, it ingests tiny larvae (microfilariae), which circulate in the dog’s bloodstream. In the mosquito, the microfilariae will mature over the next two weeks to become an infective stage. The larvae are then injected into the dog by the mosquito when it bites another dog. The larvae mature in your dog, as they travel from the point of bite through the tissues to the heart and lungs. The whole process lasts about six months. At that point, these adult worms begin producing baby heartworms, called microfilariae, which circulate through your dog’s body, waiting for a mosquito to ingest the microfilariae so they can infect another animal. It goes around and round.
The majority of infected dogs will have multiple worms that measure 10 to 12 inches long and can live inside the heart and pulmonary vessel for up to 7 years.
Heartworm prevention works by killing the larval heartworms that are developing on your dog, before they mature. The preventatives do not stop your dog becoming infected, but they do kill the infection before it can become an adult. Preventatives are given at recommended intervals or with a timed-release product. The medications are ineffective on more mature larvae if the larvae mature beyond the sensitive and susceptible stage. If you forget to give your dog the preventative, you shouldn’t be surprised when it tests positive for a year even if everything is on track.
Natural Heartworm Prevention
Holistic veterinarians claim that dogs with vibrant health can withstand an infestation of heartworm larvae injected by mosquitoes infected with the disease. Holistic veterinarians may also argue that dogs who are fed a fresh or home-prepared commercial diet and have not been treated with pesticides, but only lightly vaccinated will have the strongest immune system and be able eliminate heartworm larvae. The vet may recommend herbal or homeopathic remedies for the dog to control the heartworm infection.
It’s a good idea, but the claims are not backed up by any scientific evidence. They only come from anecdotal reports. Wild wolves and coyotes, who are not exposed to pesticides or vaccines, and eat a “natural” diet have similar rates of heartworm infection.
Heartworm prevention: How to strengthen it
You can help your dog fight heartworms by tackling mosquitoes in addition to heartworm prevention. According to the American Heartworm Society, using a registered EPA mosquito repellant such as K-9 Advantix by Bayer/Elanco or another ectoparasiticide that is effective against mosquitoes will increase the effectiveness of your heartworm preventative program. Avoid standing water and do not exercise your dog outdoors during times when mosquitoes are most active, such as dusk or dawn.
AHS recommends that annual tests include microfilaria and antigen testing (adult heartworms). Microfilaria is the first larval heartworm, which is born when a mature female worm mates with a male heartworm. The larvae cannot grow further until they’re eaten by a mosquito in a blood meal, but can become so many in the blood of the dog that they block blood vessels and can damage the liver and lungs. Most veterinary practices only recommend antigen testing at this time. Microfilaria testing is reserved for dogs that test positive for the antigen. However, there are a few situations where a dog can test negative for antigen even if they have heartworms. The presence of microfilaria confirms a diagnosis of heartworm infection. Testing should begin at seven months and continue annually.
Why is it important to test your dog even if you give the correct dose at the right time and are diligent about giving it all year long? There are many ways in which a preventative programme can fail. Heartworms are resistant to current drugs that control them. Dogs can vomit their medication without their owners noticing. The annual heartworm screening test can detect adult heartworms in your dog before they cause organic damage to their heart and lungs. Heartworm disease will only be detected when your dog begins to show signs of heart failure. It is then too late.
Drug resistance is a concern
All FDA-approved heartworm preventatives, including ivermectin and selamectin (as well as milbemycin and moxidectin), belong to the same class of drugs, the macrocyclic lactones. This means that we’ve been treating our dogs with the exact same heartworm treatment since 1987, when Heartgard was first introduced. The parasites have had plenty of time to adapt to this drug, resulting in resistance.
A second factor that could contribute to the increase in drug-resistant heartworm populations is that there are no guidelines for withdrawing approval of a heartworm prevention drug if it is found that resistance has been documented. This issue should be addressed in conjunction with the new standards to get a heartworm prevention FDA approved.
Why is it that there are not more classes and types of heartworm preventative drugs in the United States. The FDA’s standards for drug approval may be so strict and difficult to meet that they discourage drug makers from seeking approval and developing new medications. The FDA is working to change its approval process for heartworm prevention products in response to growing concerns about resistance to macrocyclic lactones. This should mean that we can expect to see newer and better medications in the future.
Heartworms are on the rise
Heartworm infection is on the rise in both this country and other countries. Climate and environmental changes are among them, as is the increased movement of dogs throughout the country.
Heartworms need a large number of mosquitoes and canine hosts to survive and thrive. The following factors promote increased numbers:
Climate change: Increasing global temperatures and humidity favors mosquito population growth, as does increased incidence of hurricanes, flooding, and other wet weather phenomena.Environmental changes: As more and more undeveloped land is taken over for human habitation, wildlife habitats are infringed upon, forcing wild canids to move closer to areas inhabited by humans and domestic dogs, increasing the numbers of heartworm host reservoirs obviously not on preventatives. Construction often alters the natural drainage of land, resulting in standing water that promotes mosquito growth.
Avoid trying to extend the time between heartworm prevention doses by writing down when your dog’s monthly dose is due. Getty Images
The popularity of foster and rescue programs that save unwanted and homeless animals from euthanasia has also led to an exponential increase in the movement of dogs between states. It would be ideal if these dogs were tested for heartworms and treated before they are transported. However, this is not always feasible. Many dogs are only tested for adult heartworms and not microfilaria. This means that even if they test negative for adult heartsworms, these dogs could still carry the heartworm disease to their new location. This leads to the spread of heartworms across the nation.
In certain parts of the United States – mainly in the Southeastern States – there has been a documented parasite resistance against the FDA approved heartworm preventions. This is a major concern, similar to those raised by the increasing number of bacteria resistant to antibiotics in human medicine. Without newer and more effective medications, we will not be able to fight disease as resistance increases.
There are many reasons why resistance occurs. The reasons for resistance are numerous. Genes and parasites can mutate over time, making organisms more resistant to medications. The weakest and most vulnerable parasites will be killed while the genetically resistant, stronger individuals are left to multiply.
Another factor in the development of drug resistance is a failure to follow recommended dosage and intervals. If you skip doses or give a lower-than-recommended dose of heartworm preventative medication, again, only the weakest, most vulnerable parasites are killed, leaving the strong to survive and multiply.
Do not get complacent
Heartworm disease is a common problem in dogs. It’s easy to get complacent. You’re aware of it, you buy and give your dog preventative, and you test your dog every year. The results are always negative. You may feel that heartworm is not a big deal because the test results are always negative. It is still a serious issue. There are several factors that are causing the situation to worsen (see the sidebar “Why the Heartworm threat is growing” above). Don’t let your dog fall behind in heartworm prevention. Infections can cause serious damage and have side effects and costs that are far more expensive than preventing them.
Best Heartworm Prevention Whole Dog Journal