National Heartworm Awareness Month

        As we enter into the month of April here at Clinton Veterinary Hospital, I am reminded that April is National Heartworm Awareness month. As I read that statement, I nodded my head in agreement— yes, this is an important subject and pet owners should be fully informed as an active participant in their pet’s health. As a part of every wellness visit, I ask if the pet is on heartworm preventative. It is so routine, integral and, ingrained in my every day job; I sometimes forget to take a step back and really explain why it is so important. Why do we advise you to buy this monthly preventative medication? Why do we recommend treatment even during a New England winter? Why is an annual 4DX test so important? Allow me to answer those questions, and hopefully shed some light on this routine but vitally important practice of monthly heartworm prevention.


     Heartworm disease can be a severe condition that results in cardiac, lung and other organ damage. It is a disease that is spread by Dirofilaria immitis-a parasitic worm. The larval stages are carried by the mosquito (intermediate host) and injected into the blood stream of the definitive host (the dog) when the mosquito bites to feed off the host. Once the larva is injected into our pets’ bloodstream they travel around and mature in the chambers of the heart. It takes about 6 months for the larva to mature and become adults and to start producing more off-spring. Your cat can also get this disease, but is considered a more resistant host to initial infection. Just for a quick comparison—a dog can handle up to a burden of 30 worms before clinical signs begin while just 2 worms can cause your feline friend to have symptoms.

     Other wild carnivores, like the lovely coyotes and foxes around Clinton, CT can also be carriers of this disease. Also, wouldn’t you know, sea lions can be carriers? So, you can see how easy it is for mosquitoes to keep passing the larval stages to different hosts (our beloved pets)?

Life Cycle of the Heartworm



     A yearly 4DX (heartworm, lyme anaplasma and ehrlichia test) allows us reassurance that your pet can continue on the monthly medication. If owners miss a dose or even give a dose late, the larva can survive in the bloodstream. That is why it is very important to give the medication at the same time each month and do the yearly test.

     We recommend our patients start heartworm medication right away; usually at 8 weeks. Since it takes about 7 months for the parasitic heartworms to mature and start producing babies, we preform the first 4DX test at 1 year of age. Our adopted pets who come to us at a later age (7 months or older), are the ones we test first before implementing a monthly regiment. This monthly preventive is something called a Macrocyclic Lactone. This class of drug can also work against some intestinal parasites like hookworms and roundworms-bonus!


     The signs of a heartworm infestation in cats and dogs can vary.  The clinical sign we see most often in both species, is coughing. Since the life cycle of the parasite ends with adult maturation in the heart the normal function of the heart is affected. This can lead to the clinical signs we see. Besides coughing, some other symptoms often seen are gagging, weakness at home and a decrease in appetite. Cats can sometimes only present with vomiting. Heartworm infection can also lead to heart failure in our pets.


     Once it is confirmed a dog is positive for heartworm disease by the 4DX and confirmed with a test sent out to a laboratory, we can initiate treatment. This process can be quite extensive and expensive—involving months of treatment and rechecks. If the dog is already in heart failure, surgery may be needed to remove the worms.

     Unfortunately, at this time, there is no approved treatment for cats, leaving prevention as our best course of action.


     Some of you may be asking yourselves; “If heartworm is transmitted by mosquitoes, why do we have to give heartworm medications in the winter months? Especially here in this region, where we can have brutally low temperatures and three feet of snow?” The American Heartworm Society recommends year-round prevention due to the changing mosquito species. Some of these species are adapting to live in colder temperatures and others are successfully surviving indoors. Therefore, giving your pet the heartworm medication each month is very important for preventative measures.

Heartworm Incidence Map of 2013

Heartworm Incidence Map of 2013

     Overall, having your pet on monthly preventative is the best solution to avoiding this disease. It is important to us all that your pet lives a healthy life, and if a simple monthly pill can help them live longer and disease-free, isn’t it worth it? For more information visit the link provided below or ask our Doctors and staff at Clinton Veterinary Hospital next time you are in about these preventatives. We are currently running a special if you buy 12 months of Heartgard, you get a 12 dollar mail in rebate!