Heart Worm - the silent killer

Heartworm is a fairly common and often fatal disease of dogs if not diagnosed and treated. Actually, it is a global disease of the dogs.  Unfortunately the average pet owner has little knowledge about the disease. Quite often, the disease sets in insidiously and eventually leads to the death of the dog.  Here are the salient aspects of the disease.

 Cluster of Heartworms in the pulmonary artery & right ventricle

What is heartworm ?

As the name suggests, it is a worm about 12 inches to 14 inches in length and about 2-3 mm in thickness. This worm gains entry in the dog’s body owing to a mosquito bite. Yes, you read it right ! This disease is indeed transmitted by a mosquito. This at least theoretically means  that the disease can occur at every place that has a mosquito population. More specifically at all places that are host to the mosquitoes responsible for transmitting the disease.

So what is the bad thing about the disease?

It’s serious and complex. The adult heartworm lodges itself in the pulmonary artery in the heart. It gets its nourishment from the blood that courses through the artery. The number of worms  can be from a few to about 100. The presence of the worms cause mechanical obstruction in the flow of the blood besides causing inflammation. Sometimes the blood may even clot. In general, higher the number of worms, severe is the disease.

What are the symptoms ?

Unfortunately, initially, there are no symptoms. However, as the number of the worms increase most dogs will develop a cough. They will get winded easily (exercise intolerance). In severe cases abnormal lungs sounds can be heard. Dogs with heavy heartworm load may collapse and die if they are subjected to strenuous exercise. Often the symptoms manifest six months after the mosquito bite.

What is the treatment ?

Generally, the treatment is planned after assessing the severity of the disease. Further, a diseased dog may have adult worms, only immature worms (microfilariae) or mixed population of adult and immature worms. Drugs (ivermectin and related drugs ) are available in the market that kill the immature worms. Now, killing the adult heart worms is a different ball game. Presently, there is only 01 drug (Milbemycin Oxime) that is supposed to kill the adult worms. Unfortunately, it is not available in India. Further, an adult heartworm that has been killed by the drug runs the risk of floating around the blood vessels. In certain cases after confirming the worm load by radiological aids the adult worms are also extracted out by surgical means.

What is the prevention ?

Monthly administration of ivermectin tablets / injections to dogs residing in endemic areas keeps the disease away.

Technical Stuff

Technically inclined visitors may watch the video "Davey's Gift from Dr Garner" at You tube where in 86 adult heartworms have been shown being extricated from the jugular vein of Davely a golden Lab. 

A visit to www.marvistavet.com and then reading the entire info on the disease is highly recommended. The info is actually fascinating. Professionals in the field and fellow vets must visit the same.