Role of Ivermectin in Preventing Heartworm Disease and Killing Heartworms

In 1987 the approval of Ivermectin presented a massive invention in heartworm prevention. For the first time, preventive medicine could be given once a month instead of daily. These medications use a very low dose of Ivermectin which is sufficient to kill any baby heartworms (L3 and L4 stages) which are swelling the skin tissues of pet at the the time when the medication is given. This way infection occurs but it is halted when the medication is given every month.

Heartworm Disease

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Heartworm disease is a scary parasitic infection that is mostly contracted by dogs. This infection is spread through mosquitos and can infect cats, dogs and other mammals such as coyotes, foxes, skunks, raccoons, squirrels etc.

As the name suggests, heartworms live inside the heart and blood vessels of infected dogs and other mammals. When a mosquito bites a dog that is infected with heartworms, that mosquito sucks the blood containing heartworm larvae. When the same mosquito again bites an uninfected dog, the larvae get transmitted to that dog.

The popular monthly heartworm prevention treatment using Ivermectin prevents the transmission of heartworm through mosquitos and preventive treatment kills the larvae that the dogs have been exposed to in the past months.

The problem with this kind of treatment is that there are various larval stages of heartworms and all of these stages are not susceptible to preventative treatments. Missed doses of medicine can allow the larvae to mature past the stages where preventative treatments are effective thus, consistent use is highly crucial when it comes to preventative disease.

Does Ivermectin Kill Heartworms?

Ivermectin is a common drug used for heartworm prevention in dogs and cats. It is also prescribed off label and extra label for treatment of various internal and external parasites such as treatment of ear mites, demodectic mange, scabies, hookworms, roundworms and capillaria in dogs. In cats Ivermectin is used for the treatment of ear mites and cat scabies.

Ivermectin significantly kills microfilaria preventing the infected dog from being a reason for contamination. Ivermectin kills L3 and L4 larvae which prevents new infections. Ivermectin may not kill adult heartworms. It sterilizes adult heartworms and cuts the lifespan of adult heartworms.

In order to kill all microfilariae (immature worms), Ivermectin needs to be given at higher doses than the regular dose recommended for heartworm prevention. It should be recommended to use Ivermectin 50 mg/kg instead of 5 mg/kg.

Treating Heartworm Infection In Dogs

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The American Heartworm Society suggests heartworm disease treatment in dogs with Melarsomine injections that kill adult worms. This treatment is called Adulticide Therapy. For some pets who are suffering from certain health conditions which can make adulticide therapy risky, veterinarians may prescribe Ivermectin treatment to gradually kill worms. This treatment is called the slow-kill method.

Slow Kill Method to Kill Heartworms

This treatment involves the administration of Ivermectin-based products (Tri-Heart Plus, Iverhart Plus or Heartgard Plus) in dogs with heartworm disease. These drugs can be given with or without an antibiotic (Eg. Doxycycline).

It is a less expensive treatment and is called the slow kill method as it may take a longer time to completely treat a dog infected with heartworm disease. Some pets may even take up to a year or more to completely eradicate adult heartworms.

Adulticide Therapy

Immiticide treatment begins quite similarly to the slow slow-kill method. The initial steps include giving the dog an Ivermectin products in combination with Doxycycline same as the slow kill method.

However, rather than continuing these drugs for months, Melarsomine is administered a month after completing the Ivermectin and Doxycycline. Melarsomine injection is administered into the back muscle of the dog.

The American Heartworm Society recommends getting three individual injections for your pets. The First and second injections should be 30 days apart and the second and third should be one day apart.

Usually, veterinarians prefer keeping the dog under observation for an initial few hours after getting an injection. They do so because medication may cause discomfort for the pet and the vet can watch for symptoms of pain.

What is Heartworm Prevention?

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Several dogs and cats in the US have been diagnosed with heartworm disease. Heartworm preventives for pets is a major concern for pet owners. Prevention is an essential part of providing vital care to your pet and heartworm disease prevention is something every pet owner can do.

The American Heartworm Society evaluates that over a million dogs in the US have heartworm disease that can be fatal. Not just dogs but ferrets and cats can also develop heartworm disease. Heartworm infections are spread through mosquitos which means any region with mosquitoes is likely to develop heartworm infection.

Heartworm preventives act by treating heartworms that already infected the pet within the past month or months. In the meantime, preventives should be given at the right time for effective results. The concerned authorities recommend year-round heartworm prevention for dogs and cats.

Heartworm preventive treatments are safe, effective and inexpensive however if a dog acquires an infection, heartworm treatment can be difficult as well as expensive requiring months of veterinary visits and exercise restrictions.

Heartworm preventive treatments are accessible in various forms such as monthly chewable pills, topical spot-on medications and an injectable medication that is administered every 6 to 12 months. These treatments are available only when prescribed by a veterinarian.

Heartworm Preventive Treatment for Dogs

Heartworm disease is a treatable disease but it is not convenient and safe to treat. That is why prevention is the best solution. Medications meant for heartworm infection prevention are used to intermittently kill larval heartworms that have managed to enter a dog’s body.

Today pet owners have access to various heartworm preventatives to prevent heartworm infection. You can pick for once a once-a-month oral prevention option, a once-a-month topical prevention option and injectables that can be administered by your vet every 6 or 12 months.

If you are a pet owner and concerned about your dog’s risk of getting heartworm disease or not sure which heartworm preventive solution is the best fit for your dog, talk to your veterinarian and seek advice.

Can Heartworm Preventive be Given to Heartworm Positive Pet

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Usually, no reaction occurs when Ivermectin-based preventives are given to heartworm-positive pets. Giving Ivermectin products that are meant for heartworm prevention to an infected dog is the initial step in the treatment of heartworm disease.

Ivermectin kills the emerging larval forms (baby heartworms) and removes circulating microfilariae (newborn larvae) making the dog unable to transmit its infection. It also minimizes the count of adult heartworms to be killed in the next phase of treatment when the particular adult worms are addressed.

If the larval worms die too fast, dogs may experience a shock-like circulatory reaction. That is why the American Heartworm Society suggest to get the initial dose of Ivermectin under veterinary supervision only. It allows the pet to be monitored for several hours following the oral dose in case any trouble occurs.

Ivermectin not only kills microfilariae but also overpowers reproduction in female adult worms and shortens the complete life span of adult worms. As mentioned above Ivermectin does not kill adult heartworms but it reduces the life expectancy of these worms.

Resistant Heartworms

Some strains of heartworm can be resistant to heartworm preventives as reported by some pet owners in the delta area. Commonly the resistance has occurred as a result of the improper use of preventives such as the slow kill method.

Particularly in this geographic region, it is essential to treat known heartworm infections promptly and not to miss doses of preventives. Although not all strains of heartworm in this particular area are resistant, make sure to avoid mosquito contact in the preventive regimen for dogs in this region.

Is regular monitoring required while the pet is getting Ivermectin Treatment?

Although low doses of Ivermectin used in Heartworm prevention do not cause problem in any breed, some breeds may experience Ivermectin sensitivity because collie associated breeds have some issues.

For dog breeds with the potential of existing Ivermectin sensitivity, screening needs to be done ahead of drug administration. DNA testing can be done to determine whether a dog does or does not have a genetic mutation that can be responsible for adverse reactions to this drug.

If a dog with mutation get the drug may experience severe, fatal reaction known as Ivermectin toxicity. Dogs may ingest Ivermectin not just in form of heartworm preventive but also if they accidently eat manure of livestock which were treated with this drug for parasite control.