A Review of Heartworms

Heartworms and heartworm prevention for your dog and cat.  This is such an important part of caring for dogs AND your cats.  Yep, both.  We don’t talk about heartworms in cats as often, and many clients do not realize that they can even be a problem for our feline friends.  But it is something we need to discuss more often.  And we need to work diligently to prevent them. Heartworms are aptly named, as they become residents of your pet’s heart.  That detail alone should inspire a degree of fear in pet owner’s hearts.  Clearly, an intruder into the heart is going to create potentially life threatening problems! The next factor that should get the attention of those not yet impressed-  heartworms are transmitted by mosquitoes.  Ever see any of those around?  Of course, we know what  a nuisance those are for Georgians.  They love our hot, humid environment.  They are ubiquitous, indoors as well as outdoors.  They are very good at their job of finding a meal, and they don’t mind flying in to our homes to do that. So no pet is safe, even the cat that never steps outdoors. And all it takes is a single bite to our cat or dog, from an heartworm carrying mosquito, to change our pet’s health status for the long term. So what is going on?  Mosquitoes carry the larval stage of the heartworm, a microscopic creature called a microfilaria.  These are picked up when the mosquito feeds on a animal that is already infected with heartworms and has microfilaria circulating in their blood stream.  When that mosquito takes a blood meal from the next pet, it leaves behind microfilaria.  Those microfilaria circulate around the pet’s blood stream, maturing, and ultimately growing into worms that will settle in the heart and begin producing their own microfilaria.   While microfilaria are microscopic, the adult heartworm most certainly is not.  These are easily seen with the unaided eye, looking a bit like angel hair pasta.  There can be so many adults present in the heart that the begin to push through the major blood vessels from the heart to the lungs, and can certainly interrupt blood flow enough to cause a heart murmur, and eventually signs of heart failure. Pets may begin to show exercise intolerance, develop a cough, and generally lose body condition.  In late stages, they can begin to have swelling in the legs and abdomen as the heart fails (This is in dogs). In cats, heartworm disease tends to be more insidious. They sometimes show no signs. Or perhaps they cough intermittently.  Perhaps they vomit, but otherwise seem normal on a day to day basis. A cat will sometimes die unexpectedly, never having shown any signs of illness or given any clues that they had heartworms. While dogs may have huge numbers of heartworms in their heart, not surprisingly causing serious effects, cats may have catastrophic results with only 2 or 3 worms. So why the difference? As the relationship between a parasite (in this case, heartworms) and a host (dogs) evolves, a balance is struck to allow the parasite to continue to use its host for a longer time. It would not be in a parasites best interest to quickly kill their host, as they require the host in order to survive long enough to reproduce.  The worms develop means to avoid stimulating the dog’s immune system too much. This way they are not attacked and removed immediately.  It also results in the dog’s response being less violent, and the decline in the dog’s health to be more gradual.  It is an intricate dance that has developed over too many generations to count. But for cats, the story is different.  They are not the natural host for the heartworm. They have not evolved together.  Therefore, the cat does not have real tolerance for the heartworms, and the worms are not very good at hiding from the cat’s immune system. Very few worms are needed to set stage for a violent reaction on the part of the cat’s body.  It is generally not a gradual, visible decline.  Once the precipice is reached, the fall over the edge is sudden and usually unexpected by the pet owner. But what about treatment for heartworm infection? Yes, we have had a medication called Immiticide to treat heartworm disease in dogs for many years. It has been a successful process for most dogs.  Those that have not developed serious changes associated with the infection, and with no other unrelated health issues will generally go on to have very normal lives.  However, the treatment, necessary associated lab work and monitoring, are generally rather costly.  And certainly more expensive than monthly heartworm prevention. More concerning, the medication is not easy to come by these days.  What most veterinarians kept on the shelf for easy use when needed, is no longer so readily available.  In some cases it is unattainable, due to a cessation of manufacture in the United States.  In order to get the needed medication, we have to call the drug company and present the case of the pet that we need to use it in.  It is a triage situation, and if our case is not the most pressing, we may not be able to get the medication right away. We have to focus on prevention of this disease, rather than treatment after the fact.  It is extremely preventable with familiar medications like Heartgard and Interceptor, and now less expensive, but still effective generic versions.  This is one of the most important things you can do for your pet’s health! As for cats… well treatment is not a realistic option. They do not tolerate the medication as dogs would, even it was readily available.  And because of the low numbers of worms needed to create a problem, we may not even be able to detect the infection prior to a tragic ending. The good news,  prevention is readily available for cats as well  Heartgard for cats is an option that has been around for a good many years, and has proven well tolerated and effective.  This does require getting your cat to eat a chewable treat, which is not always so easy.  If your cat doesn’t like this method, their are great topical medications that prevent heartworms too. Revolution and Advantage Multi are spot on medications that control fleas as well as prevent heartworms (available for dogs as well as cats, in case you have a canine companion that is suspicious of all medicinal “treats”). This is a battle that can be won. But it does require a commitment on the part of pet owners of cats and dogs alike.  This is one of the basic necessities of pet care, along with vaccines, proper nutrition, and appropriate training, exercise and lots of love! Heartworm prevention, one dose, once a month, all year long, for your dog AND cat. By Dr. Kristen Arp Bay Creek Mobile Veterinary House call appointments are available! 678-863-9408  www.baycreekmobilevet.com drivingdogvet@bellsouth.net