Heartworm (dirofilariasis) is a disease that is usually found where mosquitoes are in great number. Caused by a worm and mosquitoes (the latter are required to advance the immature worms to adulthood) the worms are usually found in the heart and surrounding vessels of dogs. Worms can also be found in other areas of the dog's body but this is an exception, rather than the rule.

Worm Lifecycle

The worms can live for as long as 5 years and the female is capable of producing millions of young. The immature worms (also known as microfilariae) are ingested by mosquitoes. Inside the mosquito they develop for approximately 20 days and then enter the insect's mouth. When the mosquito next bites a dog, the worms are transmitted into the dog's blood stream where they will complete their life cycle and begin to reproduce.

Transmission and Outward Diagnosis of Heartworm

As you may have guessed, the primary method by which this disease is transmitted is through the mosquito. Direct dog-to-dog contagion does not happen. It can take the larvae as long as 7 months to reach adulthood, so it is rarely a young dog that is diagnosed with the disease.

Outward signs of contagion include:

• Uncharacteristic behaviour e.g. acting nervous, listless and general physical weakness.

• A cough may be apparent: it will be dry and may be very persistent.

• Lack of circulation following exercise may cause the dog to faint.

• Swelling in the abdomen or legs caused by the accumulation of fluid.

• Weight loss

• Anaemia

If the animal appears to display any of these characteristics (especially the latter two - more common in advanced cases) it should be taken to see a local veterinarian immediately. The vet will examine the dog's chest with a stethoscope to determine if there are any unusual sounds emanating from either the heart or lungs.

Heartworm prevention is the best cure, so it is important that the dog should have monthly medication that your local veterinarian can provide for you. This medication can be administered through the mosquito season (differs according to climate). However, should your dog be unfortunate enough to contract Heartworm Disease, there are treatments available.

Treatments

The drug that is used contains arsenic in sufficient proportions to kill the worms and not the dog. Although it is possible for this drug to kill the dog, fatalities are extremely rare. Dogs that have weak kidneys and liver may experience problems in expelling the arsenic. If heartworm disease is too far advanced for this treatment, it is simpler to attempt to treat any damaged organs, although the dog's life span will not extend much further than a few weeks (possibly a few months).

Adult heartworms are killed using a drug that is injected into the dog. It takes approximately 30 days for this treatment to be wholly effective. The dog needs complete rest with no exercise for one month following treatment. The dead worms end up in the lungs but are broken up so the body can reabsorb them. The dog will have a cough for approximately 7 weeks following treatment if it was severely infected by the worms.

Treatment of Microfilariae

One month after the dog has been treated for the infection of adult heartworm, it will be required to visit the animal hospital once more. At this stage a drug will be given to the dog to kill the microfilariae and the animal will be required to remain at the hospital for that day. A test will be done after approximately 7 to 10 days to ascertain if the microfilariae have been vanquished. If there are some remaining then the treatment has to be repeated, otherwise the treatment is finished.

With extreme infestations of heartworms the dog may have to be treated with:

• Antibiotics

• Drugs: to bolster the health of the dog's heart before heartworm treatment begins

• Special diet(s)

• The elimination of accumulated fluids via the use of diuretics

Sadly, dogs with a chronic disease of the heart will require treatment during their entire lives. The treatment will incorporate such things as: diuretics, aspirin, drugs for the heart and dedicated diets (ideally with minimal salt and low levels of protein).

After Treatment

The owner of the dog should be gratified by the improvement in the dog's constitution. The dog will be healthier and full of life; appetite should return and the dog should make up for any weight loss quite quickly. It is important that the dog does not have to experience this disease again; re-infection is possible. Consult with your veterinarian about administering a regular drug to your dog to prevent heartworm from infecting your pet once more.

Adapted from : www.animalclinic.com