Heartworm Disease

Heart ... worms...

Hmm. Most people actually don't know what they are, how their pets can acquire such a strange disease, and why it's bad. Interestingly enough, heartworm disease is actually considered to be more a disease of the lungs than of just the heart itself. So heart / lung worms... :] I am actually writing a paper about how heartworm disease (or HWD) affects the pulmonary artery in dogs for my physiology course, so I'll post it once I am done.

If I tried to answer the first three statements right now, I would probably go into an extremely dense and detailed response.... apparently I've been reading far too many scholarly articles. Simply put, cats, dogs, and other mammals acquire HWD from mosquitoes. Sidebar: unfortunately mosquitoes are one of nature's favorite vectors and they kill thousands of humans and animals alike. The heartworms take many months to grow and will eventually make a home for themselves in the right part of the heart; the right side of your heart is responsible to pushing deoxygenated blood into the lungs, picking it up, and sending it off to the rest of your body! The simplest part, why is it bad? Well... any parasite living in the heart .... bad for many, many reasons. My paper will answer most of that.

What I really wanted to write about today was treating the disease. A couple of weeks ago, we had a heartworm positive 10 month old puppy at work. Now when you have a puppy, you will typically start heartworm prevention immediately (6-8 wks of age) and then test your pup's blood in a year to ensure they are negative for the nasty parasite. We only need three drops of blood, enough for the fancy eight minute test to determine whether or not the blood is heartworm antigen free.

For those of you who need a quick biology recap, an antigen is a substance in your body that evokes the production of antibodies. When an antigen enters your body, your immune system is stimulated to create antibodies to fight that particular antigen off.

So, antigen tests used in veterinary clinics will detect specific antigens primarily found in adult female heartworms. Most commercial tests will detect infections when mature female heartworms are at least six months old. This is exactly why you must start prevention as soon as possible! If ONE mosquito is carrying baby heartworms, better known as microfilaria, and it feeds on your dog, they will become infected. Preventing with just ONE monthly heartworm pill actually kills microfilaria, but it is NOT capable of killing adult worms. 

Now unfortunately, there is NO treatment for heartworm disease as of right now. The only pharmaceutical company to have created an approved drug for treatment, Merial, has been dried out since 2009. According to several sources, Merial has not released a reason for the shortage of the drug, called Immiticide, but has only said that there are "technical issues" in manufacturing.

Since I was curious what we would do for this poor 10 month old puppy, I decided to read about her options and here is what the American Heartworm Society recommends to do (for now):

"With Immiticide unavailable, the American Heartworm Society (AHS) has issued guidelines for treating heartworm-positive dogs to try to mitigate the damage that heartworms cause while in the body and the danger they present when they die. Briefly, here is what the AHS advises:

1. Verify all positive antigen tests with a second antigen test from a different manufacturer.
2. Give monthly heartworm preventive medication to prevent further infection. If the dog tests positive for microfilariae, pretreat with corticosteroids prior to giving the first dose of heartworm preventive medication and keep the dog under veterinary observation for at least 8 hours afterwards, due to the risk of anaphylactic shock from the rapid die-off of the microfilariae.
3. Treat dogs with doxycycline at the rate of 10 milligrams per kilogram of body weight twice a day for four weeks (give half as much if a dog cannot tolerate the higher dose). Repeat this dose quarterly (one month on, two months off) for as long as the dog is infected with heartworms. This will reduce the possibility of the infection being passed to other dogs through mosquitoes, shorten the lifespan of the adult worms, and lessen the chance of adverse side effects from worm death.
4. Restrict all activity and limit all exercise, as the danger from adult heartworms increases with physical activity.
5. Dogs with symptoms from the heartworms should receive medical treatment to alleviate respiratory distress. Surgical removal of the worms should be considered if cardiac function is affected.
6. When Immiticide becomes available, proceed with treatment if the dog still tests positive for heartworms."

On that note, I should really go work on that paper.... Have a good night :D