Heartworms are a significant parasite of the gulf coast area, and indeed has become endemic in most areas of the U.S. However, here in Louisiana, heartworms cause more deaths in younger pets due to the fact that the mosquito is the vector and a host for the parasite, and the mosquito is present year-round in our area. We also have large populations of stray and wild dogs (coyotes) to complete the life cycle.
What pets are affected? Dogs are the primary host, and in our area, we see close to 100% of the outdoor dogs who are not on any preventive medication being positive for infection. Interestingly, one study showed that 83% of the "indoor dogs" (as defined by the owner) not on prevention were also positive. Cats are also at risk for the disease, at a rate of about 15% of that in the local dog population. In cats, the dying heartworms cause serious allergic reactions and death. We now also know that many cases of Feline Asthma are actually a reactive lung disease from the presence of Heartworm larvae, even if they don't progress to adult heartworms. This syndrome is called HARD, or Heartworm Associated Respiratory Diease, and can have lifelong implications for affected cats. Ferrets (and even the sea lions at the Audubon Zoo) are also at risk and should be on preventive medications as well.
How are heartworms spread? Heartworms are spread by mosquitos, which is a year-round problem in our area. A dog with heartworms has larvae, or baby heartworms, in its bloodstream. A mosquito then takes a bloodmeal off of that dog, and ingests heartworm larva. These larvae mature in the mosquito and are transmitted to another dog, cat, or ferret by the bite of this mosquito. Up to 7 larvae can be transmitted with each bite.
How do these worms cause disease in my pet? Each of these larvae can mature into a worm in the blood vessels of the lungs and in the heart that is only 2mm wide but can be up to 7-9 inches long. These worms block the flow of blood once their numbers increase, causing right-sided heart failure. Dying worms and larvae release substances that can also cause severe allergic reactions in some animals, especially cats.
What are signs my pet has heartworms? The signs most often cited in cases of canine heartworms are weight loss with a cough, and exercise intolerance. In our area, we see many dogs who skip the signs of a more chronic disease and they present instead with severe signs of right sided heart failure that seem to appear suddenly. These dogs usually show weight loss but with a distended abdomen (from the fluid buildup due to heart failure). They may also show jaundice from liver involvment and dark, coffee or orange colored urine as well. Dogs with these signs, often referred to as "Caval Syndrome" have severe disease and are much more difficult to treat.
Cats often present differently with heartworms. In the cat, we can see asthma-like signs that can be permanent from even a transient infection with larva. If a cat does develop an adult heartworm infection, it is many times only one or two worms. However, when these worms die, the only sign the owner may see is sudden death due to severe allergic reaction.
Can I have my pet treated for heartworms? Yes and no. Dogs can be treated with a drug that can kill adult heartworms if they are diagnosed early enough to survive the die-off of the heartworms in the heart and lungs. A heartworm test at the annual exam helps insure that we diagnose any accidental cases as early as possible so the treatment can have an increased likelihood of going well. Pets who are very ill have a poorer prognosis for a straightforward treatment and cure. A detailed sheet on the different stages and cost of heartworm treatment for your dog can be obtained from our hospital.
Unfortunately, there is no effective treatment for cats or ferrets at this time, so our treatment of these pets is to prevent reactions to the presence of the worms. This can be done by treating the pet with antibiotics that kill bacteria in the worm that cause some of the problems, and with steroids that prevent inflammation. However, the lung disease caused by the presence of heartworm adults and/or larva in cats has been found to be permanent.
How can I prevent heartworm infection in my pet? Heartworms can be prevented in dogs, cats, and ferrets by using a medication administered monthly to kill a certain stage of the parasite. These medications are very safe and over 99% effective (see details below under "guarantee") . Three general catagories are available, and all products prevent some internal parasites as well. Oral monthly medications are available as chewable or regular tablets (Heartgard, Interceptor and others), and there are also liquid products that are applied to the skin (Advantage Multi and Revolution). The third catogory is an injectable given twice a year (Proheart 6). Products are also available that include flea prevention (Advantage Multi, Revolution and Trifexis). Speak with your veterinarian to determine which product would be best for your pet and your lifestyle.
Great Tip: A client recently shared a great tip for remembering to give their dog his prevention on time every month. Setting the date at the 1st of the month is one way to stay on track, but even these milestones can slip past us when we are busy. He shared that he sets the 1st as a recurring appointment in his phone, so he gets a reminder alert at the first of every month to administer his pet's prevention!
To conclude: The best way to avoid the expense and distress of having a pet with heartworm disease is to prevent it. Simple, inexpensive (many less than $8 per month) medications exist that are very effective in preventing infection even in our area. Heartworm testing at the annual exam insures that we catch inadvertent heartworm disease early enough for uncomplicated treatment. Pets who are showing signs of severe infection and heart failure may not survive the treatment, and if they do, they generally incur significant additional charges for the more intensive care they require.
And remember...A dog on heartworm prevention that is given properly and on time (with a purchase history in our records that matches this) will have most if not all of their treatment subsidized by all of the major manufacturers (see details below under "guarantee"). Problems with these guarantees arrise when people use product obtained from friends (left over from a deceased pet) , or some internet sources, or changing products without follow-up heartworm testing. Also, gaps in prevention are common, and the purchase history will show this as, say, a 6 months supply being sold, with the next one bought 9 months later = 3 months of the pet not being protected. Protect your pet and yourself by giving only heartworm prevention purchased through your regular veterinarian and giving it on time and by the correct weight of the pet.
Heartworm "Guarantee" Information and "How did my dog get Heartworms?"
- Dogs on prevention have a positive rate in our hospital of less that 1%. That is equivalent to the sucess rate of the birth control pill. However, we do see failures. The alternative, not being on prevention, puts your pet at high risk of infection. We are seeing new species of mosquitos from southeast Asia (through ports such as Houston and New Orleans) that have taken residence here. These mosquitos are more aggressive feeders, not only biting more often but biting all day. This combined with some resistance to preventions by some lines of heartworms, and some individual dog issues with the function of their immune system, makes it possible that some pets taking prevention become positive for heartworms.
The good news is that if the pet has been on the proper product and dose, the manufacturer will provide us with the means to treat the pet for heartworms. For extremely large pets, there may be some out of pocket expenses for some medications. The unfortunate part is that some pets will have medical issues and complications during that treatment that are not covered by these companies. Rest assured that we do everything we can to prevent these issues. Even with slight "hiccups" in the road to recovery, your pet is best served by ridding their system of heartworms - a highly fatal condition if left untreated.