Heartworm Disease Treatment and Prevention

Why using a heartworm preventative for your pet is an essential wellness practice

Are you aware of heartworm disease?  Could you tell if your pet was showing heartworm disease clinical signs? Do you medicate your dog or cat with a monthly heartworm preventative?  All are crucial questions owners must ask themselves to prevent their pets from testing positive for this avoidable infectious disease.

What is heartworm disease?

Heartworm is a blood-borne parasite spread by the bite of an infected mosquito.  Our canine or feline companions can become infected by the bite of a single mosquito and a potentially life threatening illness will develop.

Heartworm is the common name for Dirofilaria immitis, a parasitic nematode (roundworm).  There are four classes of heartworm disease which show clinical signs increasing in severity with progression of class.

  • Class I– Pets affected by Class I heartworm disease exhibit no to very few signs of illness, such as a mild cough.
  • Class II– Pets affected by Class II heartworm disease are more prone to coughing, exercise intolerance, weight loss, and general unkempt appearance.
  • Class III– Clinical signs become more severe during Class III heartworm disease, including anemia (low red blood cell number), respiratory difficulty, and right-sided heart failure.
  • Class IV– A dog or cat suffering from Class IV disease has episodes of collapse, shock, and multi-organ system failure.

Where does heartworm disease exist?

Heartworm disease is common in climates that are warm and humid.  In the southeast U.S., mosquitoes are seemingly present on a year round basis.  In the northeast U.S., mosquitoes seasonally thrive in the summer and fall and die during winter’s cold.

Even in regions that aren’t well known for having a high mosquito burden and prevalence of heartworm, the disease can be spread.  I live in Los Angeles where it is frequently warm and arid but not humid.  The County of Los Angeles Department of Public Health reports heartworm disease as being uncommon, but vectors harboring the disease exist in wild populations of animals (coyote, fox, etc.) or domestic animals having been displaced from natural disasters occurring in warm areas (dogs moved from southeast U.S. states after Hurricane Katrina).

You can determine if you and your pets live in a heartworm endemic area by perusing this helpful map from the American Heartworm Society: Heartworm Incidence in 2013.

Can my veterinarian test for heartworm disease?

The most common test for heartworm disease is a blood screening for heartworm antigen (the infectious organism stimulates an immune response) via ELISA (Enzyme-Linked Immunosorbent Assay).

Yet, sometimes infection with single or a few parasites does not produce a significant amount of antigen.  Plus, the antigen testing is specific to female heartworms, so an infestation with adult male heartworms may go undetected.

A more thorough approach involves pairing the antigen test with a heartworm antibody (proteins produced in response to heartworm larvae) via ELISA or other testing (direct blood smear, x-rays, ultrasound, etc.).  A veterinarian can tailor the diagnostic tests to best suit your pet’s needs.

How is heartworm disease prevented?

Although heartworm disease is uncommon in Southern California, I still suggest my patients are medicated with heartworm preventative on a monthly basis.  There is no age that I would stop giving heartworm preventative. One circumstance where a dose of heartworm preventative could be skipped would be if a dog is suffering from illness associated with a terminal disease or its treatment (such as chemotherapy) and has only days to weeks to live.

Some owners think that cats don’t need heartworm protection like their canine counterparts.  Most cats in the U.S. typically live a partial or exclusively indoor existence as compared to their canine counterparts who frequently spend time both inside and outside, but our feline friends are still at risk for heartworm disease.  Regardless of the cat’s lifestyle, appropriate measures to prevent heartworm infection are an important wellness practice.

Heartworm positive cats can exhibit clinical signs consistent with feline allergic bronchitis (asthma) and the diagnosis could be missed if the appropriate diagnostics (blood testing, x-rays, trans-tracheal wash for cytology, etc.) aren’t pursued.

Besides using heartworm-preventing medications, owners can protect their pets from heartworm disease with environmental controls.  Use screens and keep doors and windows closed to keep out mosquitoes and other biting or stinging insects.

Take your pets to the veterinarian for a physical examination at least every 12 months and follow your veterinarian’s recommendations for heartworm testing and prevention.  If a pet’s heartworm disease status is unknown or an appropriate preventative hasn’t consistently been used, then confirming a negative heartworm disease status is vital before starting a preventative.  If a pet is heartworm positive and a preventative is used, the larval form of the parasite will be killed and a life-threatening toxic response can ensue.

Pets testing negative for heartworm can receive veterinary-prescribed heartworm preventatives (ivermectin, milbemycin, moxidectin, selamectin, etc.) which should be used on a monthly basis regardless of seasonal climate changes.    The treatment for heartworm disease (typically arsenic-based, like melarsomine dihydrochloride ) is toxic to the body and has not been FDA approved for cats.

When it comes to heartworm disease, prevention is truly the best medicine, as heartworm-infected dogs or cats can incur potentially irreversible and life-threatening health consequences if the disease goes undiagnosed and untreated.  Make it a priority to protect your pet from this very preventative parasitic disease.

Meet the Author: Patrick Mahaney

Dr. Patrick Mahaney VMD, CVA, CVJ is a veterinarian and certified veterinary acupuncturist providing services to Los Angeles-based clients both on a house call and in-clinic basis. Dr. Mahaney’s unique approach integrating eastern and western medical perspectives has evolved into a concierge house call practice, California Pet Acupuncture and Wellness (CPAW), Inc. Additionally, Dr. Mahaney offers holistic treatment for canine and feline cancer patients at the Veterinary Cancer Group (Culver City, CA).

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