Causes of heartworm
Heartworms are spread through mosquito bites. Mosquitoes can carry infective heartworm larvae that enter the cat’s body when the insect feeds. The larvae move from the bite wound throughout the whole body and mature until they reach the heart and blood vessels of the lungs as adults, where they reproduce, releasing immature heartworms, also known as microfilaria, into the cat’s bloodstream. The presence of microfilaria is not very common in cats, and has been seen in less than 20 percent of infected cats. As cats have a very strong immune response to heartworm infections, more than 90 percent of infective larvae do not make it to adulthood. Those that do tend to be single-sex, and aren’t able to reproduce, which can make the detection of heartworms in cats very difficult. However, it’s important to note that the worms do not need to reach adulthood to start affecting a cat’s health.
Signs of infection
Signs of heartworm infestation in cats include coughing, laboured or rapid breathing, and vomiting. Weight loss and decreased energy are also quite common symptoms, while a physical examination might also reveal a heart murmur or otherwise irregular heart rhythm. The most common signs of heartworm disease in cats are associated with the respiratory system, such as difficulty breathing, coughing and a high respiratory rate, and are often referred to as a heartworm-associated respiratory disease. Many of these respiratory symptoms are almost indistinguishable from other respiratory diseases, including asthma and allergic bronchitis, which makes diagnosing heartworm in cats that much more difficult.
Treatment options
Most cats that are diagnosed with heartworm infection, but are not showing severe clinical signs, can easily be treated with any effective heartworm treatment for cats. Cases, where there is evidence of the disease in the lungs and associated blood vessels, can be monitored with periodic chest X-rays, along with supportive treatment in the form of intravenous fluids, oxygen therapy, cardiovascular drugs and antibiotics. When it comes to cats with severe forms of the infection, extracting the adult worms through a surgical procedure is one of the options, but be mindful of the fact that it comes with significant risk and expense.
Diagnosing heartworm
The blood tests used to diagnose heartworm in cats are unreliable and limited to detecting antigens and antibodies. Considering the fact that feline heartworm antigen tests only detect mature female heartworms, they have a high rate of false-negative results. When it comes to antibody testing, the accuracy of the results can widely vary depending on the stage of larval development at the time the blood samples are taken. The results are also difficult to interpret because a positive result doesn’t necessarily mean the cat has an infection, but rather that it has simply been exposed to heartworm disease. If your cat has respiratory symptoms or a positive heartworm antibody test, your veterinarian will want to take X-rays of your cat’s heart and lungs to assess the extent of damage, along with an echocardiogram that might also be useful to diagnose any associated heart disease.
Preventive measures
Keeping your cat indoors at all times does not prevent heartworm disease, as mosquitoes can easily get into any home. The key to providing year-round protection against feline heartworm disease, especially when it comes to the hot and humid climates where mosquitoes proliferate, is the routine administration of preventive medications, such as topical treatments and chewables. Many feline heartworm preventatives also protect against other parasites, such as ticks, fleas and intestinal parasites, which means that you wouldn’t even have to double up on your monthly treatments. Of course, it’s important to talk to your veterinarian first, before administering any of these medications. Cat owners can obtain additional information about this common feline disease by contacting the Heartworm Society.
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