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This is the final part of a three-part series about worms.  You can find Part One here, a discussion of tapeworms and hookworms, and Part Two here, a discussion of whipworms and roundworms.

Even though I am a very smart dog, I learn new things everyday.   Today, I learned that heartworms, once thought to be exclusive to canines, now affect felines as well.  Cats always try to copy everything we do, but I bet this is something they wish stayed exclusive to dogs.  If you have a cat, please talk to your vet about their heartworms.  I know nothing about the disorders of cats, except their general disability of not being a dog.

Vets rarely diagnose puppies under one year of age with heartworms, but they are still susceptible.  In fact, it can take up to 7 months for the larvae to mature into adult heartworms.  Most heartworm positive dogs will not show any physical signs for up to 2 years.

Heartworms are quite preventable.  That is why I am saddened by every case of heartworm infestation I come across.  We do not have to get heartworms.  They spread via female mosquitoes.  When they bite an infected dog, they ingest microfilariae.  The microfilariae develop in the mosquito, eventually moving to its mouth.  Once there, the microfilariae are referred to as infected larvae.  When a carrying mosquito bites their next canine victim, the microfilariae enter the dog, growing into adulthood.  Once fully grown, they enter the blood stream and move toward the heart.  There, they will complete the life cycle, reproducing  within the heart.  The adult heartworms  then clog the heart and major blood vessels leading from it, diminishing the blood supply to major organs.  This causes the organs to weaken and malfunction.

This is a preserved German Shepherd's heart with the right ventricle cut open to allow the hearworms to be seen.

Heartworm positive dogs show signs of their condition with a shortness of breath, general weakness, a soft, dry chronic cough, nervousness, and a dramatic decrease in stamina.  They are most noticeable after any type of exertion.

It is not recommended that you start your dog on a preventative without a negative test for their presence.  Once a negative result comes, your vet will prescribe a heartworm preventative product.  However, if the test is positive, heartworm treatment is the typical course of action.  To give you an idea of what the treatment is like, imagine having a short burst of chemotherapy.  When a dog receives treatment, it is very important that he be kept at a low level of excitability, receiving plenty of rest during his weeks of recovery.

The arsenic-based drugs that the dog receives kills the adult worms within a few days.  As the worms begin decompose, the flowing blood carries them to the lungs.  The decomposing worms break up, and the body absorbs them, expelling them through their wastes.  Severe cases may develop a cough 7 to 8 weeks after treatment, as the worms are expelled through the lungs.  One month after the initial treatment, a dog receives a treatment to kill the microfilariae.  After a week, the heartworm test is repeated.  If positive, the dog may have to undergo another series of treatment.  A negative result means a few weeks of rest and the commencement of a preventative.

As you can tell, the treatment is very rough on dogs.  The best thing is preventing the heartworms.  Your vet will prescribe the preventative medication, and it is not available for purchase without a prescription.  Some people believe that over the counter wormers also work for heartworms.  They do not, and neither do the popular flea preventatives.  You dog must stay on the preventative his entire life, as dogs previously undergoing treatment can become positive again.

Since mosquitoes carry it, dogs that are outside are most at risk.  You may be aware  of my feelings on dogs living in the yard.  In case you do not, I think it is wrong.  We belong in the house, with you, happily avoiding heartworms.  If you simply MUST leave your dog outside, please get him tested and on a preventative ASAP!