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Do I really need to give my pet heartworm prevention?

April is National Heartworm Awareness Month! In honor of heartworm awareness month, we will discuss the basics of heartworm disease and answer the most common questions: Do we really need to give heartworm prevention living in Colorado and do I really need to test my pet so frequently?

Heartworm disease is a serious and fatal disease if left untreated. Heartworms are actual worms that live in the heart, lungs, and associated blood vessels. Dogs, cats, and ferrets are affected by heartworms, but heartworm disease can affect other mammalian species like fox and coyotes.

Dogs are the natural hosts for heartworms, which means they can live, mature and reproduce in the heart. Some dogs can end up with hundreds of adult heartworms in their bodies. These worms cause lasting damage to the heart and surrounding blood vessels. Cats are not a natural host for heartworm but can still be infected. When infected, they will usually have only one to three adult worms or rarely never have the adult form, which means many go undiagnosed. The immature form of heartworms can cause just as much damage as the adult worms and there is no approved treatment in cats. Therefore, prevention is the best option in dogs and the only option in cats.

Q. How do pets get heartworm disease?

A. Heartworms are spread through mosquitoes. When a mosquito bites an infected animal, they ingest the immature form of heartworm called microfilaria. Once inside the mosquito, the microfilaria develops and mature into the infective stage, larvae, over 10-14 days. The mosquito takes another blood meal and the infective larvae are deposited into a new animal. Once inside the host, the larvae can take up to 6 months to mature into adult heartworms.

Q. How do I know if my pet has heartworms?

A. In the early stages of the disease, your pet may not show any signs at all. The longer the infection persists, and damage begins, is when clinical signs may develop. Signs in dogs can be coughing, exercise intolerance, fatigue, and eventually congestive heart failure. Dogs with heavy burdens of heartworms can suddenly collapse and even die due to blockage of major blood vessels. Cats can show symptoms such as coughing, asthma, weight loss, vomiting or difficulty walking. Unfortunately, sometimes the only sign in a cat is sudden death.

Q. Why do I need to test my pet so often or even at all?

A. Heartworm disease is a life-threatening disease and is progressive. The signs of infection can be subtle or even non-existent early during the disease. The only way to diagnose heartworm disease is through a simple blood test. Catching the disease at its earliest will ensure a positive outcome. While heartworm preventatives are highly effective, many factors can result in a failure in protection. If you are late giving the medication or miss a month, this could leave your pet unprotected. Annual testing is important to ensure the prevention is working. Your veterinarian can guide you on the correct timing of testing. If your pet has never been on prevention, many veterinarians will perform a heartworm test to ensure your pet is negative at the start. Giving heartworm prevention to a pet with adult worms, while rare, could be very harmful.

Q. I live in Colorado, do I really need to give heartworm prevention to my pet?

A. YES! Heartworm disease has been found in all 50 states. While some states have a higher risk than others, heartworm disease is everywhere. Many states have areas within the state that are higher risk due to the wildlife populations and mosquito populations. Travel to other states can put your pet at risk as well. There has been an increase in prevalence in Colorado due to the influx of pets from out of state shelters. Mosquitoes can come indoors, so even indoor only pets are at risk. Treatment is very painful, costly, and dangerous. There are too many reasons why you should protect your pet with year-round heartworm prevention.

Q. Why do I need to do heartworm prevention year-round?

A. Climate variations are leading to the impossible task of predicting when your pet will need heartworm prevention. Mosquitoes are adapting and changing to be better suited to certain climates. Many can survive over winter indoors. The mosquito season can be different from the northern part of the state to the southern part. Changes in wildlife roaming patterns can change the infection rate. There are just too many variables to predict, which is why the American Heartworm Society recommends year-round heartworm prevention. The American Heartworm Society has incident maps taken every 3 years showing the location of heartworms throughout the United States. It has changed every reporting. This means that every 3 years, data is collected and it is different every time. Trying to predict when to give prevention and when not to is a risk we are unwilling to take.

There are many different types and kinds of heartworm prevention available from injections, unflavored tablets for the allergy sufferer, chewable flavored tablets, and spot-ons. Talk to your veterinarian about the best option for your pet.

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