Stages of Heartworm Disease in Dogs

Heartworm is an infection that affects a large number of dogs every year. Unfortunately, this is an infection that can kill a dog if it is not treated quickly. Luckily, with proper preventative treatments, dogs will never have to suffer through the painful stages of this infection.


There are four to five stages of heartworm infection, depending on the model used by any one vet. Determining what stage of heartworm a dog has generally requires the use of blood tests and an X-ray to determine the extent of the worms within the body of the dog. Identification usually starts with the dog presenting with symptoms of heartworm, leading the veterinarian to look further into the possibility of heartworm infection.


The first stage is usually found in young and otherwise healthy dogs. There are little to no changes visible on an X-ray, which makes the diagnosis at this stage quite difficult. The second stage will allow for some changes to be detected through X-ray but the symptoms are limited and are often not enough to alarm a pet owner. At stage three most dogs are experiencing an acute infection with many side effects. At stage four and five dogs are at a critical stage, which can and often does result in death.


The effect of the disease is dependent upon the stage of infection. At the first stage the infection is still totally reversible and most of the time permanent damage has not been done. At stage two most dogs present with coughing, although it is often not severe enough for some pet owners to have their dogs seen by a vet. At stage three the dog will present with more shocking symptoms such as breathing problems, constant coughing and weight loss. At this stage there is usually kidney and liver damage. At stages four and five a dog will often go into shock and often cannot be saved or will require surgery to have a chance at survival.


The risks associated with this disease are many. First and foremost, if dogs are not treated they will die because this is not an infection that will correct itself. Instead, the worms will continue to breed and multiply and will eventually take over the body of the dog until the dog can no longer live without medical intervention.

Dogs who have heartworm also pose a threat to other dogs. The infection is spread through mosquito bites, so a dog that has heartworm can be bitten by a mosquito that then goes and bites and infects another dog. One dog with heartworm can infect countless other dogs as a result.


Heartworm is a completely preventable and treatable infection. The idea is to prevent infection with heartworm medication that is given to the dog on a regular basis. The medication is given on a monthly basis to kill off any worms that could be residing in the dog. For dogs that are already at stage two to three, treatment involves an injection of medication into the spine that kills the worms quickly and effectively but is much more invasive. Of course, for dogs who are at an advanced stage of infection, surgical methods may be their only hope.