Heart Worm

HEARTWORM (Dirofilaria immitis)

The heartworm (Dirofilaria immitis) is now recognized as a major, global pest affecting many animals but particularly dogs. It is caused by a parasite which breeds inside the arterial vessels of the dog having been transmitted there by a mosquito bite. A lot of mosquito species are carriers of the infectious stage of the heartworm which is mainly a summer disease between April and October.

And, as in the Tick Disease, the female is the transmitter. From the site of the infection, the small dirofilaria larvae start a subcutaneous migration of several weeks, until they reach the circulation which carries them to their main breeding place, the right heart chamber and the main lung artery. They can also lodge in the veins of the liver and the veins entering the heart. And it is from here that they cause a bloodstream blockage causing serious damage to the dog’s circulatory system. In advance cases this can lead to heart failure and sudden death. The first sign of heartworm infestation may not manifest for a year after infection, and even then the soft cough that increases with exercise may be dismissed as unimportant by the owner. But the cough worsens and the dog may actually faint from exertion, he tires easily, is weak and listless, loses weight and condition, and may cough up blood. Breathing becomes more difficult as the disease progresses. The progression is traumatic: the dog’s quality of life diminishes drastically and he can no longer retrieve a Frisbee or take a long walk in the park without respiratory distress. Congestive heart failure ensues, and the once-active, outgoing pet is in grave danger.

The success of treatment depends upon the stage of infection.Treatment before the appearance of heart insufficiency or oedemas, which is a medical term to describe the build up of fluid within the lungs, is easy and successful. It comprises of two injections against the adult worms and a consecutive oral treatment against the larvae which infect the blood stream. Advanced cases are very difficult to treat as they require the surgical removal of the worms in the heart and lungs, followed by the complete rest of the dog for one month with special anticoagulant therapy and later on, the anti-heartworm therapy described above. But it’s like anything, prevention is better than cure. To prevent Heartworm consult your Vet who will probably advise an annual injection of which the details are entered into your dog’s Pet Passport. Prevention can also be given orally in the form of a tablet every month between April and October.