How Often To Heartworm Dogs

It is advised by the American Heartworm Society to “think 12.” Every 12 months, get your dog tested for heartworms and provide them 12 months of prophylactic therapy.

The Dessau Veterinary Clinic offers numerous types of heartworm prevention therapy. Along with a six-month injection, there are monthly chewables and topical treatments. Depending on the specifics of your beloved dog’s health and requirements, our veterinarian staff can assist you in selecting the best course of action. A few of the products also offer protection from additional parasites.

Heartworms are spread by mosquitoes, and the risk increases as the temperature warmer and mosquitoes are harder to avoid. However, this does not imply that prophylactic measures should end when mosquitoes are less active. The drugs may be effective in the past, stopping the spread of illnesses that occurred months ago.

Heartworm illness is a terrible condition. The parasites can survive for years inside a dog and can grow up to a foot long. Depending on how bad the dog’s illness gets, medicine might not be sufficient to get rid of them. The pet may require surgery from a veterinarian to have the heartworms removed from the organs. Even though the worms will be gone, the harm that has already been done will still be present, so it is critical that your pet receive preventative care all year long.

How often do dogs need to be treated for heartworms?

All FDA-approved heartworm preventives operate by destroying the larval stages of the heartworm parasite, regardless of whether you choose to take the treatment orally, topically, or intravenously. This covers both the mosquito-delivered infectious heartworm larvae and the subsequent larval stage that grows inside the animal. Unfortunately, heartworm larvae can metamorphose into an immature or juvenile adult stage in as little as 51 days, at which point preventives are ineffective. Heartworms must be eradicated before they mature, thus it’s crucial to apply heartworm preventives exactly when they’re supposed to be used (monthly for oral and topical products and every 6 months or 12 months for the injectable). Applying preventative measures too late may cause poorly prevented molting of immature larvae into the adult stage.

Do dogs require monthly heartworm medication?

You will undoubtedly want to do everything in your power as a loving and caring owner to protect your dog from this terrible illness. The good news is that heartworms can be completely avoided.

Your dog must be tested for heartworms prior to beginning prophylactic medication. In fact, any veterinarian in Ponte Vedra Beach, Florida will urge that heartworm testing is either included in or suggested as a result of an annual wellness visit for your dog. This is due to two factors. First, to make sure his preventative medication is effective, and second, because heartworm infestation symptoms frequently don’t show up until there are a lot of them in the body. Dogs are experts at masking their illness, and they will continue doing so until they are unable to do so any more. Similarly, heartworm symptoms typically don’t manifest until the child reaches adulthood, or around seven months after contracting the infection. If your dog tests positive for heartworms at the outset, treatment must be completed before prevention may start. If your dog is healthy, you can start him on a monthly dose of medication to ward off the illness.

Heartworm preventatives come in a variety of forms and are typically administered monthly. These include monthly medications that you can smuggle into his food and topical insect repellents that you apply to his skin. There is already an injectable preventative as well that will offer your dog up to six months of protection. The most crucial thing to keep in mind with any preventative is to adhere to the schedule of dose administration as advised by your veterinarian. Being even a few days late puts your dog friend at danger of getting heartworms. Keep detailed records of the times you provide your preferred prophylactic, and set reminders for the subsequent dose. Consult your veterinarian if you’re unsure which preventative to pick.

Do dogs require annual heartworm treatment?

There is a 250,000 to 1 in 50,000,000 chance that a dog will contract heartworm disease each year, which equates to one in 200 dogs.

Find the contradiction in the following list of assertions: Heartworms can be fatal to dogs and cats and cause serious lung illness. People contract zoonotic diseases from heartworms. By giving them medication once a month that also treats numerous internal and external parasites, heartworm illness in dogs and cats can be avoided. Each year, around 250,000 canines are diagnosed with heartworm infections. 1 However, there isn’t any justification for giving dogs preventives all year round; it’s just not necessary.


Let’s now perform some math. There is a 250,000 to 1 in 50,000,000 chance that a dog will contract heartworm disease each year, which equates to one in 200 dogs. You have a one in 200 risk of receiving a cancer diagnosis this year, which is the same likelihood that a dog would have heartworm disease. 2 However, heartworm infection in dogs is almost completely avoidable. Would you take a monthly prescription to avoid developing cancer this year? However, there isn’t any justification for giving dogs preventives all year round; it’s just not necessary.


Let’s now examine the available heartworm treatments. There is no medication authorised to treat heartworm infections in cats, however dogs can be treated with the arsenical melarsomine dihydrochloride. The dosage of melarsomine is 2.5 mg/kg. In mongrel dogs, the LD50 for organic arsenic is 14 mg/kg. 3 Melarsomine overdoses of three can be fatal. 4 The EPA has set the limit for arsenic in drinking water at 10 parts per billion5, or 10 g/L, based on a no-effect risk of 1 to 10,000 to 1 to 1,000,000. You would therefore consume 100 g of arsenic per day, or 36.5 mg of arsenic per year, if you drank 10 L of water each day that contained the maximum permitted level of arsenic. Two injections totaling 250 mg of melarsomine, which has a 37.5 mg arsenic content, are given to a 50 kg dog. To receive the same quantity of arsenic used to cure heartworm illness in a dog, it would take one year of consuming water with high arsenic levels. Therefore, the dose required to eradicate canine heartworms is by no means little. However, there isn’t any justification for giving dogs preventives all year round; it’s just not necessary.


Arsenical therapy is undoubtedly far preferable to the long-term effects of big worms residing in their hosts’ pulmonary arteries. In the wake of treatment, the lungs do improve. 6 The male and female adult heartworms are both around 1 mm in diameter and range in length from 12 to 20 and 25 to 31 cm, respectively. 7 Even if a dog only carries 12 worms—six men and six females—that is still a significant number of worms in the pulmonary arteries.

The worms’ interaction with the pulmonary arteries’ surface results in a persistent illness.

8 In addition to physically rupturing red blood cells, the presence of the worms in the bloodstream causes hemoglobin to be deposited inside of fixed macrophages in the lungs, giving dogs with chronic heartworm infections brown lungs. The development of tiny thrombi that travel deeper into the lungs and ultimately cause chronic lung illness is another effect of villous proliferations on the arteries.

But remember that despite treatment, the worms are in the pulmonary arteries and not the digestive system. After receiving arsenical therapy, the only thing that may happen is that the worms are pushed deep into the lungs, where they eventually die in tightly wound bundles, decompose, and are eliminated by the host’s immune system. Remember that each dead worm is around 20 cm long, so this process takes a while and is not without consequences. However, there isn’t any justification for giving dogs preventives all year round; it’s just not necessary.


Don’t forget to account for nature’s unpredictable behavior. Although it is known that Culex tarsalis mosquitoes may survive for up to two months in temperatures that remain at 77°F9, there is a good likelihood that they could survive for longer in colder climates. More than half of the female overwintering Culex territans mosquitoes investigated survived more than 138 days at 23 F near George Lake in Alberta, Canada. 10 If these mosquitoes are infected with heartworms in October, they might still easily transfer the infection during an exceptionally warm December, like the one we had this year in Ithaca, New York. These mosquitoes will continue to seek blood meals whenever they are about to lay eggs. These microclimate conditions put dogs at danger all year long, which is one of the reasons why the capc guidelines recommend that dogs receive preventives all year long. There seems to be no good reason for a dog to be at risk in a pleasant November or in a warm March, given locally acquired heartworm transmission probably occurs in any state. However, there isn’t any justification for giving dogs preventives all year round; it’s just not necessary.


Maybe we could learn something from our colleagues in human medicine. Mosquitoes that bite sick people spread human lymphatic filariasis, a condition brought on by heartworm relatives. Elephantiasis brought on by the condition is terrible. Small, thread-like worms that inhabit the lymphatics inflict crippling and severely disfiguring sickness on their human hosts. Through “bulk drug administration tactics for disease elimination,” the World Health Organization is leading the effort to eradicate these parasites. 10 The rate of infection in humans and vectors has significantly decreased as a result of these population-wide mass therapies. 11 We can only hope that, in the future, such restrictions on the spread of heartworms would help to lessen the incidence of the debilitating illness that heartworms in dogs bring on.

Professor of parasitology at the Department of Microbiology and Immunology, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, is Dwight D. Bowman, MS, PhD.

How often should I take heartworm medication?

If it’s okay to provide the monthly heartworm preventative every 45 to 60 days, this question comes up frequently. When I inquire as to why she/he would want to do that, the pet parent replies that she/he read online that giving a heartworm preventative every 45 to 60 days rather than every 30 days is safer.

Unfortunately, the knowledge obtained from “Dr. Google” is completely false and harmful! Due to the heartworm’s lifestyle, the monthly heartworm preventative we prescribe only lasts in a dog or cat’s body for one to two days, not 30. Therefore, the pet only needs to take the heartworm preventative every 30 days. Waiting every 45 to 60 days is ineffective from a safety standpoint because the medication has already left the pet’s body when the next dose is scheduled to be administered. Giving the drug every 45 to 60 days rather than every 30 will likely prevent juvenile heartworms from becoming adult heartworms because of the heartworm life cycle. In other words, taking heartworm preventive medicine every 45 to 60 days does not work.

As I’ve noted in prior posts, the medicine manufacturer will pay for the cost of therapy if a pet contracts heartworms while taking the monthly heartworm preventative obtained from our hospital, as per their guarantee. However, if the drug is administered every 45 to 60 days, this guarantee does not apply.

You chose us for care in part because you want to avoid overmedicating your pet and are worried about their safety. We agree with you and will only recommend medication if we believe it to be secure.

How many heartworm medications are required for dogs?

This leaflet offers details on canine heartworm disease therapy. Consult the handouts “Heartworm Disease in Dogs” and “Testing for Heartworm Disease in Dogs” for more detailed information on the causes, transmission, and testing techniques of heartworm disease in dogs.

What causes heartworm disease?

Dirofilariasis, sometimes known as heartworm disease, is a dangerous and possibly fatal condition. It is brought on by the parasite Dirofilaria immitis, which lives on blood.

Infected dogs have adult heartworms in their hearts, pulmonary arteries, and nearby big blood vessels. Worms may occasionally be discovered in other areas of the circulatory system. Female worms are 1/8″ broad and 6-14″ long (15-36cm) in length (3 mm). The size of males is roughly half that of females. When diagnosed, a dog can have 300 worms present.

Infected dogs’ hearts, pulmonary arteries, and nearby big blood vessels all contain adult heartworms.

Heartworm adults can live for up to five years. Millions of microfilaria, the females’ progeny, are produced throughout this period. These microfilariae primarily inhabit the tiny blood arteries.

How is heartworm disease spread?

The disease is not transmitted from dog to dog directly because the mosquito serves as an intermediary host in the transmission process. Therefore, the disease’s spread correlates with mosquito season, which in many regions of the United States can persist all year. The prevalence of heartworm disease in any given area is closely connected with the number of affected dogs and the length of the mosquito season.

My dog has been diagnosed with heartworm disease. What is the treatment?

Although fatalities are uncommon, treating dogs for heartworms carries some risk.

More than 95% of dogs with heartworms can now be successfully treated thanks to a new medication that has fewer adverse effects.

In the past, the medication used to cure heartworms contained significant amounts of arsenic, which usually resulted in toxic side effects. More than 95% of dogs with heartworms can now be successfully treated thanks to a new medication that has fewer adverse effects.

When they are diagnosed, many dogs already have advanced heartworm disease. Consequently, the heart, lungs, blood vessels, kidneys, and liver have sustained significant harm as a result of the heartworms’ protracted presence. Rarely, cases may be so severe that treating organ damage and providing the dog with comfort is preferable than risking the side effects of heartworm treatment. The lifespan of a dog in this condition is most likely limited to a few weeks or months. Your vet will provide you advice on the most effective course of action for treating pets with advanced heartworm illness.

a method to eradicate adult heartworms. To eliminate adult heartworms, melarsomine (marketed under the name Immiticide) is administered via injection. Adult heartworms in the heart and surrounding arteries are killed by melarsomine. A series of injections are used to give this medication. The precise injection schedule will be decided by your vet based on the health of your dog. Most dogs have a first shot, a 30-day rest period after that, and then two further injections spaced 24 hours apart.

In order to prevent infection with the bacteria (Wolbachia) that live inside the heartworm, many dogs will also receive treatment with an antibiotic (doxycycline).

Following treatment, total rest is necessary. Within a few days, the adult worms pass away and begin to rot. In the lungs, where they lodge in the tiny blood vessels after fragmenting, they are finally reabsorbed by the body. The majority of post-treatment difficulties are brought on by these pieces of deceased heartworms, and their resorption can take many weeks to months. The dog must be kept as quiet as possible during this potentially dangerous time and must not be permitted to exercise for one month after receiving the final injection of heartworm medication. Because the worms are dying during the first week following the injections, this period is crucial. Many dogs with severe infections continue to cough for seven to eight weeks following treatment. For treatment alternatives if the cough is severe, contact your veterinarian.

If the dog experiences a major reaction in the weeks after the initial treatment, prompt treatment is crucial, albeit such reactions are uncommon. If your dog exhibits depression, fever, intense coughing, shortness of breath, blood in the cough, or loss of appetite, call your veterinarian right once. Anti-inflammatory medications, antibiotics, cage rest, supportive care, and intravenous fluids are frequently effective treatments in these circumstances.

a method to eradicate microfilaria. Your dog will also receive a medication to kill microfilariae in addition to the medication used to treat adult heartworms (heartworm larvae). On the day that this medication is given, your dog might need to stay in the hospital for observation; this could happen either before or after the injections for adult heartworms. Your dog will begin taking a heartworm preventive after treatment.

“Various medications are used in more recent heartworm treatment protocols to kill the microfilariae.”

Various medications are used in more recent heartworm treatment procedures to kill the microfilariae. Based on your dog’s condition, your veterinarian will decide on the best medication and timing for administration.

Are any other treatments necessary?

Prior to receiving treatment for the heartworms, dogs with severe heartworm disease may need to take antibiotics, painkillers, special diets, diuretics to eliminate fluid buildup in the lungs, and/or medications to improve heart function. Some dogs might need lifelong heart failure medication even after the heartworms have been eradicated. Diuretics, heart drugs like beta-blockers, ACE-inhibitors, or cardiac glycosides, as well as specialized low-salt diets, are all examples of this.

What is the response to treatment and the prognosis post-treatment?

Dog owners are frequently taken aback by their dog’s improvement after heartworm treatment, especially if the dog had been displaying clinical heartworm disease symptoms. Many dogs exhibit increased vitality, better appetites, and weight gain.

How can I prevent my dog from getting heartworms?

Using a heartworm preventive will help you keep your dog’s heartworms at bay. After a dog has undergone a successful heartworm treatment, it is crucial to start a heartworm prevention regimen to avoid recurrence. No pet should ever have to deal with the terrifying disease thanks to the safe and economical heartworm preventives that are currently accessible. To find out which heartworm prevention strategy is best for your dog, speak to your vet.