Heartworm basics

Heartworm is an insidious disease that is found in virtually all parts of the United States and Canada. Heartworm disease is spread only by mosquitoes; thus it follows that areas with high concentrations of these insects tend to have a greater incidence of heartworm disease.

As the name implies, a heartworm lives in the blood of a dog's heart and adjacent blood vessels. The adult heartworms live in the heart and produce offspring, called microfilariae, that circulate in the infected dog's blood.

When a mosquito sucks blood from an infected dog, it also sucks out the microfilariae. After spending two weeks in the mosquito, the microfilariae become infective larvae, a necessary step in the transmission of heartworm. When the infected mosquito bites another dog, the infected larvae are transmitted.

Detection and treatment

Veterinary researchers have developed medications and procedures that have vastly improved treatment of canine heartworm disease. To ensure a successful cure, it is vital that the disease be detected and treated in its early stages.
Before administering a preventative medication to a dog, he must have a blood test to ensure that he does not have heartworms already. There could be severe, even fatal reactions, if a dog with heartworm is given a preventative medication.

The blood test can usually be performed right in the veterinarian's office, and most dogs can begin the preventative program as soon as a negative result is confirmed. If a dog shows any heartworm symptoms, or has been in an area where that are known heartworm problems, he will likely need to undergo additional testing before starting either a preventative or treatment program.

Common symptoms of canine heartworm disease include:

• Breathing difficulties
• Coughing
• Tiredness
• Listlessness
• Weight loss
• Rough coat

Some dogs do not exhibit symptoms in the early stages; others do. Heartworm can lead to congestive heart failure and death if not detected and treated.

To ensure your dog's health, many veterinarians recommend screening your dog on an annual or biannual basis, even if they are on heartworm preventives. If you live in, or are traveling into, known heartworm areas, veterinarians usually prescribe preventive medications that keep the larvae from maturing into adult heartworms. The scheduled dosing regimen for these medications must be strictly followed.

Today, most dogs with heartworm disease survive thanks to modern medications, although some may require surgery. Active monitoring and prompt detection are the best tools to prevent needless suffering. Veterinary research into all phases of heartworm disease is always ongoing. Your veterinarian is your best source for the latest advice and information.

Source: Adapted from the American Animal Hospital Association