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Heartworm in Dogs: Symptoms, Dangers, What to Do

Heartworm in Dogs

One of the most dreaded diseases dog owners must be aware of is heartworm. This is a disease that is caused by Dirofilaria immitis, a parasitic worm. Your dog can become infected when he is bitten by a mosquito carrying the worms. Basically, once bitten by an infected mosquito, your dog becomes the primary host to these parasitic worms which take up residence in your dog’s lungs, heart and related blood vessels.

The idea of these worms living in your dog’s lungs and heart may seem like something out of a horror movie but the threat is real and serious. All dogs should have a heartworm test as early as possible in life, and definitely by about seven months of age.

A negative heartworm test is great news because it means your dog can be put on preventative worm medicine so that they are protected against heartworm infection in the future. If you’re lucky, you and your dog will never have to worry about treatment for heartworm disease.

If you get a dog from a shelter or from a breeder, be sure to ask whether or not the dog has been tested for heartworm and if they are on any preventative heartworm medication.

Heartworm in Dogs: Symptoms

Heartworm in dogs can take many different forms, with several variations of infection. These gradually get worse and much more serious, requiring greater effort and care on your part.

See below to learn the different rates of heartworm infection in dogs.

Class 1 Heartworm Infection

Initially your dog may show no symptoms of heartworm infection or have only mild symptoms such as coughing once in a while.

Class 2 Heartworm Infection

Once the heartworm infection worsens, your dog may begin to show more symptoms, coughing will increase and your dog may appear fatigued after activity. An x-ray of your dog’s lungs and heart may show changes.

Class 3 Heartworm Infection

As the number of worms in your dog’s system increases your dog may now have a chronic cough and the condition of their body may deteriorate. You may notice that your dog has trouble breathing. Changes to heart and lungs appear upon x-ray.

Class 4 Heartworm Infection

This is the worst level of infection. Not all dogs will progress to this stage. At this stage, the heartworm burden on your dog is so much that worms block blood flowing to the heart. For dogs at this level, also known as caval syndrome, surgery to remove the worms is required.

Heartworm in Dogs: Dangers

When a dog is infected with heartworms, the larvae grow to spaghetti-like worms that mate and reproduce. The danger with heartworm in dogs is that your dog may not show many symptoms upon initial infection. This means if you aren’t testing your dog every year for heartworms, there can be large knots of heartworms growing in your dog’s lungs, heart, and other organs and you won’t even know it. Untreated heartworm infection can shut down your dog’s lungs, heart, kidneys, and liver, and will eventually be fatal.

Treatment for dogs that get heartworm is expensive, it’s risky, and it’s not always successful. One medication for heartworm treatment is called Melarsomine dihydrochloride, known as Diroban or Immiticide. It is a deep injection that can be given to dogs in the first three stages of heartworm disease.

If your dog gets a heartworm infection, you will need to plan for a multitude of veterinarian visits, as well as blood testing, injections, x-rays, and even hospitalization. It’s much easier on you and your dog to have them tested early in life and get them on heartworm prevention medication.

Heartworm in Dogs: What to Do

There is preventative medication you can give your dog every month that is specifically designed to protect against heartworm infestation. Be aware that heartworm prevention medication does not KILL heartworms already present in your dog’s system. You can kill your dog if you give them heartworm prevention medication when they are already infected with heartworms.

Before giving any kind of heartworm prevention medication, have a veterinarian perform heartworm testing on your dog. Dogs who test negative for heartworm can be given medication monthly to prevent infection and should then be tested at least once every year for heartworms.

If you suspect your dog may be infected with heartworms, you can have a blood test done by a veterinarian at about seven months of age. The blood test reveals whether antigens produced by adult female worms are in the dog’s bloodstream. Antigens from adult heartworms may not show in your dog’s bloodstream for up to five months after being bitten. A second test can be done to reveal any microfilariae in your dog’s blood. Microfilariae can’t be detected until about six months after you dog was bitten and infected.

Make you you check with our Dog’s Diet page to learn other ways to keep your pup healthy.