A single mosquito bite can lead to a heartworm infection, causing serious health issues for your pet. Sadly, these infections frequently go undiagnosed, because many pets don’t exhibit signs until the parasites have caused irreversible damage to their heart and lungs. Our team at 360 Pet Medical wants to provide information about this concerning condition, and to offer advice to help ensure your pet is protected from these dangerous parasites.
How are heartworms transmitted to pets?
Heartworms (i.e., Dirofilaria immitis) thrive in the heart and lungs of infected dogs. When a mosquito takes a blood meal from an infected dog, heartworm larvae are ingested. These baby heartworms mature to larval stage three while inside the mosquito, and then are deposited in the mosquito’s saliva on the next pet the insect bites. The larvae travel through the bite wound where they encyst in the pet’s skin, and mature to stage five larvae. At this stage, they are ready to migrate to the pet’s heart and lungs. Dogs are natural hosts for heartworms, and the stage five larvae are able to mature to adulthood, mate, and produce offspring in the dog’s heart. Cats are atypical hosts, and heartworms rarely reach adulthood while parasitizing a cat, but the immature heartworms are still capable of causing cats significant health problems.
How does heartworm disease affect dogs?
Since dogs are natural heartworm hosts, the parasites can grow 12 inches or longer inside the dog’s heart and lungs, and several hundred worms can inhabit a single dog. The presence of these worms causes the dog’s immune system to create inflammation in the lung tissue and pulmonary arteries, in an attempt to eradicate the parasites. In addition, many heartworms are infected by a bacteria, Wolbachia, that further contributes to the inflammatory response. When the heartworms die, body pieces can lodge inside the vasculature, obstructing blood flow to the lungs. The inflammation and improper circulation results in scarring in the vessels supplying the lung tissue, and effectively pumping blood through the lungs becomes difficult for the heart. Over time, this results in heart failure. In the initial stages, most dogs don’t exhibit clinical signs, but as their condition worsens, signs include a persistent soft cough, panting, exercise intolerance, weight loss, and fluid accumulation in the abdomen or chest. In dogs with a heavy infection, the worms block blood flow into the right side of the heart. This condition, called caval syndrome, results in labored breathing, pale gums, collapse, and potentially sudden death. Prompt surgical removal of the heartworm blockage is necessary for the dog to survive.
How is heartworm disease treated in dogs?
Exercise restriction is important in infected dogs, because physical exertion exacerbates the damage the heartworms cause to the dog’s heart and lungs. Heartworm disease treatment is extremely dangerous, because as the medication kills the parasites, the dead worms can cause life-threatening consequences for the pet. The dog’s condition must be stabilized before treatment is started, and once treatment is initiated, they will need close monitoring for complications. Dogs with a low worm burden have a better prognosis than those heavily infected.
How does heartworm disease affect cats?
Since cats are atypical hosts, their heartworms typically don’t mature to adulthood. About 75 to 90 days after the cat was bitten by the infected mosquito, heartworm larvae reach the pulmonary arteries, and the cat’s immune system responds by creating a strong inflammatory response. This causes lung disease, called heartworm-associated respiratory disease (HARD), resulting in signs, including coughing, increased respiratory effort, and vomiting, that are hard to distinguish from feline asthma. In addition, one or two heartworms sometimes mature to adulthood, and since the cat’s heart is so small, the resulting blockage can be fatal. Another possible occurrence is a saddle thrombosis. The presence of the worms in the cat’s heart can cause a blood clot to form, and if the clot lodges in the base of the aorta where the vessel branches to supply the hind limbs, the cat can experience sudden paralysis of one or both hindlimbs.
How is heartworm disease treated in cats?
Currently, no treatment is approved for heartworm disease in cats. Management focuses on stabilizing the cat, and closely monitoring their condition with frequent chest X-rays. Steroids are often used to help decrease the inflammation caused by the parasites, and antibiotics may be prescribed to address the heartworm’s Wolbachia infection, which can contribute to the inflammatory response. The average survival time for heartworm-infected cats is one and a half years.
How can I prevent heartworm disease in my pet?
The best way to handle heartworm disease is to prevent the parasites from infecting your pet. This can easily be accomplished by providing year-round heartworm prevention medication to your pet, plus yearly testing to ensure your pet remains uninfected. Many products are available to make heartworm protection convenient for you and your pet. Some products can be administered topically once a month, others can be given orally once a month, and certain medications can be given by injection once every 6 to 12 months. Consult with our veterinary professionals, to determine the best method for your pet.
Providing year-round heartworm prevention is an important part of your pet’s health care plan. If you would like to discuss the various preventives, contact our team at 360 Pet Medical, so we can determine what protocol would best fit you and your pet’s lifestyle.
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