Heartworm Disease in dogs
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Discover what heartworm symptoms in dogs are. This silent killer can be prevented with simple medication.

It is devastating when your precious pet has been diagnosed with a deadly disease but it is even more tragic to know that it could have been avoided in the first place.

Heartworm is very common in the USA with some states showing larger numbers of dogs with heartworm being recorded. Heartworm disease is expensive and difficult to treat so prevention is vital.

According to Banfield’s stats shown below, Mississippi tops the chart with 1 in 26 dogs testing positive for heartworm. It has however, been reported in all 50 States.

  1. Mississippi – 1 in 26 canine heartworm tests were positive
  2. Louisiana – 1 in 28 canine heartworm tests were positive
  3. Arkansas – 1 in 31 canine heartworm tests were positive
  4. Alabama – 1 in 60 canine heartworm tests were positive
  5. South Carolina and Texas – nearly 1 in 70 canine heartworm tests were positive

What is heartworm in dogs?

Heartworm is a devastating and potentially fatal disease found in pets in the USA and also in some other areas of the world.

Heartworms can cause heart failure, severe lung damage and can even damage other organs in your pet’s body.

They can affect dogs, cats and ferrets and are also found in foxes and coyotes.

This disease is caused by a parasitic worm called Dirofilaria immitis.

Heartworm Disease in dogs

How do dogs get heartworms?

The mosquito is the main player and host in the heartworm cycle.

Adult female heartworms that are present in a dog, coyote or wolf produce offspring called microfilariae. These baby worms are then released into the bloodstream of the infected animal.

When a mosquito bites an infected animal then the microfilariae are transferred to the mosquito.

The microfilariae then mature inside the mosquito. This takes between 10-14 days.

The infected mosquito then bites another dog transferring the larvae via the bite wound into the dog’s bloodstream.

It then takes about 6 months for the larvae to mature into adult heartworms that are then capable of reproducing.

Heartworms can live for 5-7 years and can reach a length of 12 inches.

They look like thin strands of cooked spaghetti. The worm burden can be as high as 250 in some dogs.

Every mosquito season can lead to even more heartworms infesting your pet.

Heartworm lifecycle

How often does a dog need to be tested for heartworms?

Your dog needs to be tested annually when it goes for its usual annual check-up.

If you have a puppy younger than 7 months, then they can be started on heartworm prevention medicine without doing a heartworm test.

This is because it takes at least 6 months for a dog to test positive after been infected.

It will be wise to have young puppies tested twice (once they have been started on heartworm preventatives) within the first year to make sure they stay free of heartworm.

 After that they can be tested annually.

Dogs over 7 months that are not on heartworm preventatives must first be tested before starting heartworm preventatives.

Then when they start they will need to be tested every 6 months for the first year and then annually after that.

It is really important that your dog gets the heartworm preventative every month.

Missing a single monthly dose can cause your dog to be unprotected and exposed to the risk of getting heartworms.

Testing them annually, even when they are on heartworm preventatives, is necessary to make sure that the preventative is working.

This test can be done at the same time as there normal annual check for diseases common to Cavapoos.

Heartworm preventatives are highly effective but there is never a 100% guarantee that your dog will not get this disease.

Signs of heartworm in dogs

Heartworms can be present in your dog long before any symptoms appear.

The first symptoms can be fatigue after moderate exercise, a mild persistent cough, lack of appetite and a reluctance to exercise.

As the disease progresses then your pet can develop heart failure accompanied with a swollen belly.

Sudden blockages of blood can occur when your dog has large amounts of heartworms. This is life-threatening.

Symptoms are labored and difficulty breathing, pale gums because of blood loss and dark colored urine. Very few dogs survive without immediate surgical intervention.

Cavapoo teeth

Can humans get heartworms?

Heartworm is only transmitted via mosquitoes so you cannot catch it from your dog.

But if a human is bitten by an infected mosquito then you can be infected with heartworm. This is however very rare.

Even if you are bitten, the parasite does not mature in the human body.

The typical sign of heartworm in humans is a small nodule in the lungs that is shown up in x-rays. This is just the tissue reacting to the dead parasite.

 Heartworms do not live for very long in human blood so they do not need to be surgically removed. Medication is also not necessary.


Is heartworm contagious?

Short answer is No.

Infected dogs cannot transfer the heartworms to other dogs.

Only mosquitos can transfer the heartworms from one dog to another.

Can heartworm in dogs be cured?

Most dogs that have tested positive for heartworm can be treated but the treatment is expensive and complex.

Your veterinarian will first want to confirm the test results by performing a second different test.

The last thing you want is for your dog to be treated for heartworm when it does not have any.

If both tests are positive then your veterinarian will first work on stabilizing your pet to make sure they can handle the heartworm treatment.

This can take a few weeks or even months if your pet is heavily infected or has other serious health conditions.

The veterinarian might already start your dog on heartworm preventatives while stabilizing it. This helps to stop further infections and keeps your dog from being a source of heartworm larvae infecting more mosquitoes.

Your dog’s daily activities will be restricted because physical activity increases the rate at which the heartworms cause damage to the lungs and heart.

If your dog has severe symptoms then you can expect your dog to be heavily restricted and you will probably be told to keep them in a crate to avoid as much damage as possible.

Once your dog is stable then your veterinarian will begin the necessary treatment. This involves several steps depending on how severe the disease is.

Dogs that have no or mild symptoms have a high rate of success.

Severe cases can be successfully treated but complications can occur.

A drug called Melarsomine is injected into your dog. This needs to be done at a veterinary hospital.

This drug kills the adults worms quickly which are then eliminated within a 1 to 3 month period.

Cage rest will be necessary with reduced exercise to avoid complications.

Several other medications can also be used to help make sure the treatment is a success.

One of these is to start the dog on heartworm preventative medication at least 2 months before giving them the melarsomine injection.

About 6 months after the completion of treatment, your veterinarian will need to test your dog again for heartworm to make sure it was a success and all the heartworms are gone.

Sick Cavapoo

My dog has heartworms how long will she live?

There are a lot of factors that will determine how long a Cavapoo will live for if they have heartworms but firstly let me say that treatment is available and very successful so this would be the first option.

If the dog is not given any treatment then it will eventually die from the damage that heartworms cause.

It is difficult to say how long this will take because it depends totally on the age of the dog, the size of the dog, how badly it has been infected and also what damage has already been done.

Heartworms can live for between 5-7 years but this does not mean your dog has 5-7 years. As mentioned above, there are a lot of factors involved.

Can a dog cough up heartworms?

A Cavapoo with heartworms will have a dry persistent cough which in the later stages of the disease is also accompanied with labored breathing.

This is the result of the worms causing damage to the lungs.

In dogs with advanced heartworms, your dog may cough up blood but will not cough up heartworms. They can also experience nose bleeds.

How to prevent heartworm in dogs

Heartworm is totally preventable with the monthly use of heartworm preventative medication. It needs to be administered on the same day every month and cannot be skipped.

Even skipping just one dose can result in your dog getting heartworms.

Heartworm preventative medicine for dogs

There are a few options presently available but the most common and recommended one is Heartgard Plus.

This medicine not only kills heartworms but it also helps to treat and control hookworms. It is a chewable tablet that has a beef flavour. Dogs love to eat Heartgard Plus.

Heartgard Plus is the No1 heartworm preventative medicine recommended by veterinarians.

It kills the larvae stage of the heartworm so that they cannot become adults and thus prevents heartworm disease from happening.

This medicine can be given to puppies as young as 6 weeks of age.

Heartgard contains Ivermectin and Pyrantel and needs to be stored at a temperature below 68° - 77°F and not in direct sunlight.

Nexgard Plus

Heartgard Plus comes in 3 sizes.

  1. Brown Box for dogs between 51-100lbs
  2. Green Box for dogs 26-50lbs
  3. Blue Box for dogs below 25lbs
Heartgard Plus Green Box
Heartgard Plus Blue Box

You will need to chose the one closest to your dog's weight. If in doubt then get in contact with your veterinarian and ask there advice.

All 3 boxes contain 6 months worth of treatment.


Difference between Heartgard and Heartgard plus

The only ingredient found in Heartgard is Ivermectin which means that it only kills heartworms.

Heartgard Plus contains Ivermectin and Pyrantel so this medicine not only kills heartworms but can also control roundworms and hookworms


Dangers of heartworm medication

Every dog or puppy needs to first be tested for heartworm before taking Heartgard.

The reason for this is because Heartgard Plus does not kill adult heartworms so it be will ineffective for dogs already hosting adult heartworms.

This is purely a preventative medication.

Side effects of Heartgard Plus

When using the correct dosage, then side effects are very rare.

Possible non-serious side effects include vomiting and diarrhoea.

Possible serious side effects can include central nervous system toxicity or blindness if too high a dosage has been given.

If you see any of the following signs then contact of your veterinarian immediately:

  1. Weakness
  2. Big pupils
  3. Excessive drooling
  4. Coma
  5. Being clumsy
  6. Pressing their heads against a wall
  7. Trembling
  8. Foaming at the mouth

Heartgard Plus has been shown to be safe for pregnant dogs, breeding dogs, puppies older than 6 weeks and male dogs.

In clinical trials it has been used in conjunction with antibiotics, vaccines, flea collars, shampoos and dips.

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