Heartworm Archives

December 30, 2005

Heartworm- A Realistic Look

Heartworm: A Realistic Look

Heartworm is of concern to all dog owners, and is a potentially serious, sometimes even fatal, disease. It is not, however, the unavoidable scourge that many vets and pharmaceutical companies would have us believe. If your dog is reasonably healthy, eating a SARF diet, is vaccine free, is not currently 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. In the event that some of the larvae should manage to get past your dog's immune system defenses and survive to adulthood, it is still far from a death sentence. They will be much weakened, and the truly healthy dog will make a less hospitable host. Even at the adult stage, a healthy dog, possibly with some veterinary assistance, should be able to fight them off with no lasting ill effects to his health. Nor are the currently available cures more dangerous than the preventive, as the veterinary and pharmaceutical industries would have us believe.

The mid and southern Atlantic states and the north-central states (where we live) have the most reported cases of heartworm. See the maps at Note the tremendous increase in heartworm since the introduction of mass vaccinations (figure three). Mosquitoes are the only known vector 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.

There are many sites out there on the internet with lots of "information" on heartworm. The problem with much of it is that it is either wrong or incomplete. Much of it is intended to mislead and frighten you. One site says simply that a mosquito bites an infected dog then bites another dog and infects it. While that, to some extent, in the most general of ways, is true, it is very misleading because the entire process is much more complicated and time consuming than that that explanation would lead one to believe. Another says that the mosquito injects the heartworm into your dog. This is simply false.

This is a compilation of information I've been collecting for a couple of years, including some tips on what you can do to protect your dog from heartworm. The heartworm has 5 separate larval stages referred to simply as L1, L2, L3, L4, and L5. The L5 is actually the young adult stage. The fully mature adult is often referred to as L6. In addition, 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 any further. If they are not, they will simply die of old age and be passed out of the system. Once the mosquito ingests the microfilariae from the infected dog, the larvae must go through two stages of development, or molts, changing from L1 to L2 and from L2 to L3, while in the mosquitoes system before the mosquito can infect another dog. Once the L3 stage has been reached the larvae migrate to the mosquitoes mouth. It is only the L3 larvae, which are capable of infecting another dog. This mosquito cycle takes anywhere from two weeks to about 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.

The importance of temperature: While the larvae are developing in the mosquito, development continues only when the temperature is above 64 degrees F. Further, 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. Remember, it is only the L3 larvae, which are capable of infesting your dog.

Now lets say that a mosquito has bitten an infested dog; and that the temperature has remained above 57 degrees F for a minimum of 14 days since that bite; and that the mosquito bites your dog. Still, your dog is not infested because the L3 larvae are deposited in a tiny droplet of mosquito saliva adjacent to the bite, not injected into your dog by the mosquito--as many would have us believe. Providing the humidity and temperature are such that the droplet does not evaporate before the they get the chance, the L3 larvae must swim through the saliva and into the hole left by the mosquito bite, thereby entering your dogs 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 subcutaneous tissue just under the skin, not in the blood of the newly infected dog. The L4 will continue to live and develop in the subcutaneous tissue for the next two to three months, where they develop into the L5 stage. Once they make this development or molt into the L5 or young adult stage, they then leave the subcutaneous 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.

The adult female mosquito, the only one which bites, usually lives little more than thirty days. Some species live only a couple of weeks. See, For a great deal more information on the mosquito visit,

When Is A Preventive Not A Preventive

The most popular heartworm "preventives," Heartgard and Interceptor, are not really preventives at all; rather 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. In other words they're poisons, as are all of the other popular HW preventives. None of them kills the fully adult or L6 heartworms in the dosages prescribed for prevention. At higher doses, however, some of them will.

There are basically two standard tests for heartworm. One is called the antigen or occult test, which tests for the antigens produced, by the adult female heartworm. This test does not show the presence of microfilariae. The other is the microfilaria test. This test, of course, tests for microfilariae. Both Heartgard and Interceptor kill microfilariae. Therefore, if one’s dogs have been on either of these products, they will test negative for heartworm when given the microfilaria test, even though they may be infested with adult heartworms. It is not common, but it does happen. There have been many reports of dogs having very bad reactions to both Heartgard and Interceptor. Giving one's dog doses of poison month after month to kill something, which probably isn’t there anyway, doesn't make an awful lot of sense to me.

In his book "Homeopathic Care For Cats and Dogs", under the heading Heartworm, p332, Dr. Don Hamilton says: "This is a serious disease that primarily affects dogs... It can be treated homeopathically but this should be under the care of an experienced veterinarian. Heartworm preventives are generally very effective at protecting dogs against the disease....In dogs the "monthly" preventives are effective if given at six week intervals, and possibly even at seven- or eight week intervals.... The daily preventives are almost a thing of the past, but these are usually effective if given every other day. Although the preventive drugs are generally safe, they can initiate an autoimmune disease in susceptible animals...The homeopathic nosode that is made from heartworm larva is employed commonly as a preventive to avoid the drug side effects. Many question its effectiveness, though I have several clients who use the nosode (apparently successfully) with animals in heartworm endemic areas. Most animals have no trouble with heartworms. I do know of some cases where the nosode did not protect, however. I believe it does offer some protection, though it may be incomplete... If you decide to try the nosode, you must understand that its effectiveness is currently unknown."

To me this quote says pretty clearly that Dr. Hamilton has more faith in the drugs like Heartgard than he does in any homeopathic approach to prevention.

In the Nature of Animal Healing by Martin Goldstein, DVM, he explains about heartworm.
pp. 220 - 223

"To judge by your local veterinarian's stern insistence on regular heartworm pills for your dog, you'd think we're in the midst of a brutal epidemic, leaving piles of the dead in its wake. I think there's an epidemic, too, but of a different sort: of disease-causing toxicity instilled in our pets by heartworm preventable pills.

Granted, heartworm is a serious condition. An infected mosquito bites your dog (cats are rarely affected), injecting microscopic worms that first hibernate, then gain access to his bloodstream. ... they spawn hundreds of thousands of baby larvae called "microfilaria" which circulate through the blood stream . . .

A few caveats are in order, however. Only a small percentage of dogs who get heartworm die of it, especially if they're routinely tested twice a year for early detection. Even in untreated dogs, after a period of uncomfortable symptoms, the adult worms die. The microfilaria do NOT grow into adult worms on their own To reach the next stage in their life cycle, they have to be sucked back out of the body by another mosquito and go through the other stages of their maturation process within the mosquito. Only when that mosquito alights again on a dog and bites it can the microfilaria reenter the bloodstream with the ability to grow into adults. The chances of a microfilaria-infected mosquito biting your dog the first time are slim. Of it happening to the same dog twice? VERY slim. And after two decades of pervasive administration of heartworm pills in the U.S., the chances of your dog contracting heartworm in most parts of this country even a first time are slimmer still. Early in my career, I saw and treated cases of heartworm disease, most with routine medication, yet witnessed only three deaths (the last was in 1979). By comparison, we're seeing cancer kill dogs on a daily basis. To my mind, the likelihood that toxicity from heartworm pills is contributing to the tremendous amount of immune suppression now occurring, especially in cases of liver disease and cancer, is far greater and more immediate than the threat of the disease they're meant to prevent.

The most common form of heartworm prevention is a monthly pill taken just before and during mosquito season. (Many veterinarians recommend giving it year-round, even in areas of the country that experience winter.) Its toxins -- ivermectin, for example - sweep through the body killing any microfilaria that have been introduced by mosquito bites in the previous month, and thus preventing the growth of adult worms. Some brands also contain other toxins to kill intestinal parasites. The other approach to treatment is with a daily dose of the drug diethylcarbamazine, starting several weeks before mosquito season The drugs called for in either course of treatment are, simply put, poisons. Unfortunately, while they kill off microfilaria, they have the toxic effects of poisons, and can be especially damaging to the liver. I have seen one obvious immediate effect of these once-a-month preventatives in case after case: when you give a dog that pill, over the next few days, wherever he urinates outside, his urine burns the grass. Permanently! In some cases, you can't grow grass there until you change the soil. What, I wonder; can it be doing internally to your dog in that time?

When the daily preventatives came out, I witnessed evidence of hemorrhaging in the urine of several dogs put on them. We stopped the medication; the bleeding stopped. We started it up again; the bleeding resumed.

(He goes on about places like Florida and the Bahamas where incidents of heartworm is higher, to use preventives like Black Walnut and homeopathy. Further, treatment for heartworm includes a heart glandular, vitamin E, CoQ10 and regular doses (small) of black walnut. ) ".

Here are a few of the more glaring data points collected from information submitted between 1987-2000. Note this is only the information submitted -- imagine the hundreds/thousands that don't get submitted because they vets can't/won't make the connection:

Heartgard Chewables (Ivermectin) 134 dogs died; 1033 had some type of reaction
Filaribits Plus 128 dogs died; 187 reacted
Interceptor (Milbemycin) 67 dogs died; 460 reacted

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