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Pets Blog

Canine Heartworm Disease 101

By Stephanie Sivula Published: June 11, 2012

Greetings from Dancing Paws Animal Wellness Center! We're new contributors to the Pets Blog, and are so excited to be a part of the community!

It's our hope to provide you with information about pet health and other topics relating to their medical care. Please feel free to contact us directly if there are any topics you're interested in reading about!
This post will focus on canine heartworm disease. Most dog owners have heard of heartworm disease, either because of their veterinarian's recommendation or through television ads for online pet pharmacies. But what is heartworm disease? How is it spread? And how do those monthly medications prevent it?
Heartworm disease is a blood parasite spread by mosquitoes. The life cycle begins in an infected animal, like a coyote, fox, or even another dog. Adult worms reside in the host animal’s heart, lungs, and blood vessels, producing young called microfilaria. They circulate in the host’s blood stream and are ingested by mosquitoes during a feeding.
Without the mosquito, the microfilaria will not mature. Dogs cannot spread heartworm disease from one to another; the mosquito is essential to the development and spread of the parasite.
Once inside the mosquito, the microfilaria mature and develop, and when they’re ready, they migrate to the mosquito’s stomach and mouth. They enter their next host through the mosquito’s next bite.
The heartworm larvae continue to migrate and mature through the dog’s veins. While in the early stages of development, these larvae can be killed by orally administrated heartworm preventative. That’s how the preventatives work – they are ‘retro-active’, meaning they do not prevent heartworm exposure, but kill the immature heartworms to prevent a full-blown heartworm infection. This is why it is so important to administer a preventative drug regularly during heartworm season. 
If no preventatives are used, the larvae continue to develop to sexual maturity and produce more microfilaria. Adult heartworms can live three to five years, with males attaining a length of nearly seven inches and females a whopping ten-and-a-half inches.
Symptoms of infection in early stages are simply a cough and some abnormal lung sounds. As infection progresses, dogs will have difficulty breathing, exercise intolerance, fluid accumulation in the abdomen, enlargement of the liver, and other symptoms, all potentially leading to death.
Frequently, people allege that as long as you have a healthy dog, feed a raw diet, and do not over-vaccinate, your dog will not get heartworms. Unfortunately, this is not true. Challenge studies have shown that in dogs deliberately infected with heartworm larvae, about 90% of them will develop adult heartworms. This suggests that perhaps dogs do have some natural resistance to heartworm disease, but we think it’s a serious mistake to bet your dog’s life on this notion.
There are many heartworm medications out there, with more being released every year. It can be difficult to decide what product is best for your dog. Some include treatment for other nasty bugs, like intestinal parasites, fleas and more. Look over the details of each medication and assess your dog's risk for exposure to these other parasites. If you and your canine counterpart frequent dog parks or hiking trails, boarding or grooming facilities, doggie day care or shows, their risk of exposure is typically high. In these cases, heartworm medications with extra defenses are in order.
The interesting thing about heartworm medications is that they work retro-actively. This means they work to erradicate any infection that may have occured over the last 30 days, rather than providing protection for the month after administration. The medication kills any heartworm larvea that may have been contracted, eliminating the risk of further development and infection. When the larvae have more than a month to mature, the medications can no longer provide total protection and the disease can progress. This is why it's so important to give your medication on a strict schedule.
We hope you enjoyed this blog post! It's brought to you by the staff and doctor at Dancing Paws Animal Wellness Center in Richfield, Ohio. We're a holistically minded veterinary clinic providing care to dogs and cats from all over Northeast Ohio! We invite you to check out our website here!
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