Heartworm is an insidious disease that has spread to virtually all parts of the US and many parts of Canada since the early 1970s. It is spread only by mosquitoes; thus, areas heavily populated by these insects tend to have a greater incidence of heartworm disease.

Heartworm can strike both dogs and cats, although it is much more commonly seen in dogs. As its name implies, heartworm lives in the blood of a dog’s or cat’s heart and adjacent blood vessels. The adult heartworms living in the heart produce offspring, called microfilariae, which circulate in the infected animal’s blood.

When a mosquito “bites” an infected pet, it sucks out blood containing the microfilariae. After about two weeks in the mosquito, the microfilariae become infective larvae. This step is necessary for the transmission of heartworm. When the mosquito bites another pet, the infective larvae are transmitted.

Canine Heartworm
Veterinary research has resulted in medications and procedures that have improved the treatment of canine heartworm disease. Prompt detection and early treatment are vital to a successful cure.

Highly effective diagnostic testing and preventive medications have been developed in recent years. It is necessary to have a heartworm test prior to using a preventive. Severe or fatal reactions may occur if preventives are given to dogs with heartworm disease, or may create diagnostic confusion at a later date.

A small amount of blood is all that’s necessary for a preliminary heartworm screening test that is very accurate in detecting the presence of heartworm. In many regions, this may be the only test needed before starting a preventive program. If the dog shows heartworm symptoms or has visited a known heartworm problem area, additional tests are recommended before a preventive or treatment program is started.

Common blood screening tests can verify the presence of heartworms. Radiographs or X-ray films and other sophisticated laboratory tests are used to detect heartworm disease.

Canine heartworm disease symptoms include:

  • Difficulty breathing
  • Coughing
  • Tires easily
  • Listlessness
  • Weight loss
  • Rough hair coat

In many cases, there are advanced symptoms. Some dogs do not appear to have symptoms in the early stagesJothers do. If not detected and controlled with proper treatment, heartworm can lead to congestive heart failure and death.

As a safeguard, many veterinarians recommend annual or biannual screening tests even for dogs that are on heartworm preventives. In known heartworm areas, or if dogs are traveling into these areas, veterinarians usually prescribe preventive medications. This medication prevents the larvae from developing into adult heartworms. Prescribed medications must be given as directed.

Today, the majority of dogs with heartworm disease survive. Most are cured by medications. ** Some require surgery. Prompt detection prevents needless suffering.

** Immiticide – the only drug licensed in the United States to treat adult heartworms in canine patients – is currently in short supply.  The drug manufacturer (Merial) is consulting with veterinarians on a case-by-case basis.  “This is a temporary delay and we are managing inventory to make Immiticide available to customers that have an urgent need,” the company reports in a statement.

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