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NALC Registered Breeder Since 1996

Specializing In Natural Bobtails and Natural Rearing



Heartworm - How It Works

Heartworm is a potentially serious, sometimes fatal disease. It is not, however, the canine health problem that it is made out to be. If your dog is healthy, eating a SARF diet, is vaccine free or on a minimal vaccine protocol, is not on any HW “preventives” or chemical flea and tick preventives, his immune system should be strong enough to fight off a heartworm infestation with none of the larvae reaching adulthood and without an owner even knowing about the issue.
(A dog that is eating an inappropriate diet, is over-vaccinated and has it’s system constantly bombarded with chemicals and insecticides can be a vulnerable host.)

In the event that some of the larvae should manage to get past your dog’s immune system and survive to adulthood, this is still a far way off from the parasite causing problems. Even at the adult stage, a healthy dog is  able to fight them off with no signs or lasting ill effects.
(Heartworm has only become the problem is has over the past 20 - 30 years since mass inoculations have

Mosquitoes are the only known transmitter of the infective stage of the heartworm larvae. In some parts of the country mosquitoes are a problem all year round, while in others this problem is limited to the warm months.

The heartworm has 5 separate larval stages - L1, L2, L3, L4, L5 and L6.
(L5 being the young adult stage. L6 the mature adult.)
Heartworm also has two separate cycles, which, combined, make up the total lifecycle of the heartworm. One cycle takes place in a mosquito, and the other inside a dog or cat.

When a mosquito bites a dog harboring microfilariae, the mosquito ingests the L1 larvae, or microfilariae. This can only happen if the dog is also harboring the L6, or mature adult heartworm, because the microfilariae are the offspring of the adult heartworm. These microfilariae can live for up two years in the dog’s blood without causing any harm. They must, however, be taken up by a mosquito in order to develop further. If they are not, they will die of old age and pass out of the system.

Once the mosquito ingests the microfilariae from the infected dog, the larvae must go through two stages of development changing from L1 to L2 and from L2 to L3, while in the mosquitoe’s system before the mosquito can infect another dog. Once the L3 stage has been reached the larvae migrate to the mosquitoe’s mouth. (It is only the L3 larvae which are capable of infecting another dog.) This mosquito cycle takes anywhere from two weeks a month depending on the weather. The warmer the weather, the faster the development. If the larvae haven’t made the final development by then, they never will because the mosquito dies of old age at about 35 days, and along with the mosquito, die the larvae.   

While the larvae are developing in the mosquito, development continues only when the temperature is above 64 degrees F. The temperature MUST remain above 57 degrees Fahrenheit at all times, day and night during the entire mosquito cycle. If at any time during the development into the L3 stage, the temperature drops below 57 F, the development is aborted and must start over.

If all the conditions are right –
- a mosquito has bitten an infested dog
- the temperature has remained above 57 degrees F for a minimum of 14 days since that bite
- that mosquito then bites your dog.
Your dog is still not infested because the L3 larvae are deposited in a tiny droplet of saliva bordering the bite, NOT injected into your dog by the mosquito.
The humidity and temperature must be just right so that the droplet does not evaporate entering your dog’s system.

Once inside your dog, the L3 larvae must spend the next two weeks or so developing into the L4 larvae. During this period of time the larvae are living in the tissue just under the skin, not in the blood of the newly infected dog. The L4 will continue to live and develop in the tissue for the next two to three months, where they develop into the L5 stage. Once they make this development into the L5 or young adult stage, they then leave the tissue and enter the blood stream. The L5 or young adults then migrate to the heart and pulmonary arteries where they make their final development into the L6 or mature, breeding, adult stage and attach to the tissue of the heart and pulmonary arteries. Once there, approximately 5 to 7 months after entering the dog’s body, they will mate. This mating produces the microfilariae.

If the dog is not re-infested with L3 larvae from another bite from another infected mosquito, the adult heartworm will die of old age in about 2 years. The microfilaria will also die a natural death unless taken up by a mosquito.
Again, all of this happening without the owner ever knowing there was an issue to begin with. Our dogs’ systems can take care of themselves if given the chance to by being kept strong and healthy in the first place.

Weighing The Risks


The most popular heartworm "preventatives," - Heartgard and Interceptor, are not preventatives at all.
They act by killing the microfilariae, L3, and/or L4 larvae in an infested dog.
(Interceptor kills the L3s, and L4s, while Heartgard will kill the L4s and some of the youngest L5s.)

They are chemical insecticides and when administered month after month, year after year, the toxic side-effects become a serious health risk.!!
For us, the risks are just too great to outweigh any benefits at all.
Giving a dog a dose of poison month after month to kill something which probably isn’t there anyway and if it is, will probably cause no health problems in a healthy dog doesn't make sense. All the toxicity from heartworm pills accomplish are to suppress the immune system. The side-effects of liver disease, heart problems and cancer, is far greater and more immediate than the threat of the disease they're meant to prevent.

An American Veterinary Medical Association (AVMA) report on adverse drug reactions showed that 65% of drug reactions reported and 48% of all reported deaths caused by drug reactions were from heartworm preventive medicines.

We have chosen not to give our dogs Heartworm meds every month. Instead we keep their immune systems strong by feeding them a proper SARF diet and not over-vaccinating or keeping them vaccine free and not suppressing their systems.

If an owner wishes to take safe preventative measures against heartworm, there are many natural protocols available. There are also many natural ways to treat heartworm if the problem ever does arise.

The Whole Story About Heartworm” - By Lee Cullins is an excellent downloadable PDF file e-book,
that goes into great detail regarding heartworm.

“Natural Canine Heartworm Treatment” - If you are concerned about heartworm this site has information
on a natural treatment.


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