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take heart: how to protect your best friends from heartworm

  • Dr. Kim
  • Posted by Dr. Kim Smyth on
    Staff Veterinarian and Pet Health Writer of Petplan

5 States Where Dogs Are Most At Risk For Heartworm | Petplan's Vets for Pets Blog

It’s starting to warm up all over the country. Warmer temperatures bring mosquitoes back into our lives, and with them comes your pet’s risk of contracting heartworms.

According to the American Heartworm Society, cases of heartworm disease have been found in all 50 states, and the range of heartworms is spreading every year.  Because heartworms are spread by mosquitoes, more cases are found in the Southeast, along the Gulf Coast, and along the Mississippi River.

The 2014 Banfield State of Pet Health Report reveals the top 5 states with the highest prevalence of heartworm infection are:

1. Louisiana
2. Mississippi
3. Arkansas
4. Alabama
5. South Carolina

While it is especially important to protect your pets if you live in a high risk area, remember, as the mosquitoes that transmit disease continue to migrate, so does the disease - which puts all dogs at risk. 

The life cycle of heartworms

When a mosquito takes a blood meal from an animal with heartworms, it ingests baby heartworms (microfilaria) present in the infected animal’s blood and becomes a vector of transmission.  During the next 10 to 14 days, the microfilaria develop into larvae inside the mosquito. When the mosquito bites another dog or cat, the larvae are transmitted to that animal.  From there, it takes about six months for the larvae to turn into adult heartworms.


Heartworms live in the arteries around the lungs, but as the number of worms accumulates, they can back up into the heart as well. In dogs, the average heartworm can live five to seven years, and it is not uncommon to find up to 30 or more spaghetti-sized worms in severely affected dogs. You can imagine the impact a clump of worms like this would have on the heart’s ability to contract normally.


Clinical Signs

Signs of heartworm disease in dogs are easy to miss initially, but as the disease progresses, you may notice exercise intolerance or a mild, persistent cough. In cats, the symptoms mimic other diseases, such as asthma, including the exercise intolerance and coughing seen in dogs.


Diagnosing heartworms

Testing for heartworms in dogs is easy – a simple blood test will do, and many dogs have this done at their yearly physical. Cats present a diagnostic challenge, as a negative heartworm test will not necessarily rule out heartworms. Additional diagnostics may be needed for symptomatic cats.


Treating heartworms

Unfortunately, there is no approved treatment for heartworm disease in cats. Dogs are a little bit luckier – there is an approved treatment, but it is not without its own risks. Post-treatment thromboembolisms (the blocking of a blood vessel by a blood clot dislodged from its site of origin) occasionally occur and may be fatal. Treatment in dogs involves using medication to kill off adult heartworms, as well as others to kill circulating microfilaria (thereby preventing transmission of disease).


An ounce of prevention

All of this sounds pretty scary, right? Take heart - there’s good news, too.

Heartworm disease is 100% preventable.

Many different types of heartworm preventatives are currently on the market, so whether you prefer to give your cat or dog a tasty treat once a month or apply a topical heartworm preventative, your vet has you covered. If your pet has been off of heartworm prevention, talk to your vet about scheduling a heartworm test and getting him back on his medication as soon as possible. His life depends on it.

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