This article is a continuation of subjects addressed in the article: Basic pet winter healthcare.
Everyone has heard of heartworms and unfortunately too many know pets who are no longer with us due to this disease. This is something pet owners hear far too often here in the South. How much do you really know about one of the leading causes of death of pet and stray populations of animals? Where do heartworms come from? Can it be treated safely? How is the best way to protect a pet in swampy areas? Do I need to protect my other pets such as cats? No preventative is a 100% guarantee against disease but using knowledge to determine the best preventative for your pet can stack the odds in your favor.
Heartworms or Dirofiliaria immitis is a parastic worm with a complex life cycle. We will begin the cycle at the baby or microfilaria stage. The microfilariae are discharged by the adult worm and can remain active for 1-3 years in the bloodstream; enter the mosquito. The mosquito feeding on the pet ingests the microfilariae which mature to an infective stage within 2 weeks and migrate to the mouth of the mosquito to be spread to the next unsuspecting victim. Contrary to popular opinion, this stage is not transmitted through the stinger or mouth of the mosquito but rather the worms slide down to the skin and enter the hole in the skin after feeding! The heartwom begins its life in your pet in the fatty layer of tissue just under the skin where it lives for around 2 months before beginning its migration to the heart which takes between 2-4 months. Add on another 2-3 months of maturing and the heartworms are ready to start multiplying in the heart and lungs of your pet. So in total the length of time from bite and entry to babies being evident in the bloodstream is around 6-7 months. Two different tests are available for detecting heartworms in your pet. One is a visual test for microfilariae in the bloodstream, the other is a test for heartworm antigen(molecular components of heartworms floating in bloodstream) and is dependent on a certain number of female heartworms being present.
Who can get heartworms? Although we commonly think of it as a dog disease, we often see cats suffering the complications as well. Although they have fewer numbers of adult heartworms compared to the dog, the cat however has an overactive immune system that mounts a massive reaction. Asthma, a common condition in cats, is believed to be linked to heartworm infection. Heartworm disease is high on the list of probable causes for sudden death of a cat as well. Who else can suffer from heartworms? There are reports in the literature of ferret and even a few human infections by heartworms as well.
Treatment used to consist of Thiacetarsamide intravenous injections, a quick kill solution that was often too tough on seriously ill animals. Today's treatment of choice is Melarsomine (known as Immiticide). Administered as intramuscular injections, the chemical slowly kills off adult heartworms and gives ill animals a chance at treatment. Cats are not treated for heartworm disease, its simply too dangerous.
What preventative is best for your pet? The market is flooded with every form from a chew to a tablet to liquid applications. All forms focus on killing the microfilariae when it is present in the fatty layer. This is how dogs "on preventative" can come up positive for heartworms. Once microfilariae have progressed past the fatty layer they cannot be killed by preventative! Therefore missing just a few doses of preventative and then re-starting its usage can still end up with a pet with heartworm disease.
Consider your pet when wading through heartworm preventative options. The best form for cats is a product called Revolution (http://www.revolution4cats.com/). This is a liquid placed on the skin between the shoulder blades and prevents heartworms, intestinal parasites, fleas and ear mites. Everything in one easy to administer product.
Dogs, its a little tougher. Liquids often have difficulty reaching the skin of long haired or thick coated dogs. For this reason oral tablets or chews are often preferred. Here's a simple way to approach it:
likes soft chew and not allergic to beef- Heartgard Plus (heartworms and intestinal parasites; tried and true; company backs up product- if your dog comes up heartworm positive and have 2 years of purchase documentation, the company will pay for their treatment) heartgard.us.merial.com/home/ .
your pet doesn't care about having a soft chew -go for a variety of tablets on the market just make sure they have an extra component for intestinal parasites in this area of the country.
is your pet allergic to beef? It is very difficult to find preventative without flavoring in today's market. Heartgard does make an unflavored tablet but additional protection may be needed against intestinal parasites. Consult your veterinarian for options.
is your pet at high risk of exposure such as a swampy area or property near drainage canals, etc? Pets in these areas are often dosed more frequently and at higher dosages. Consult your veterinarian for options.
would you prefer an injection every 6 months? ProHeart 6 has been re-introduced to the US market (www.proheart6dvm.com/docs/proheart_reintroduction.pdf). See your veterinarian for more information.
In short the active ingredients of today's preventative: ivermectin, selamectin, milbemycin and moxidectin all act essentially the same. In the South always include preventative against roundworms and hookworms, the most prevalent and potentially dangerous parasites. Some products also add protection against tapeworms. This should be considered for pets with consistent flea problems. Certain breeds such as the collie and its relatives (Shelties, etc) may have a sensitivity to ivermectin and so therefore milbemycin or an alternative to ivermectin may be considered.