By Lexiann Grant
Mosquito season is beginning, and it's time to protect your cat from heartworm disease. Yes, cats get heartworms too – even indoor cats are at risk since mosquitoes can enter a home when a door is open.
The life cycle of heartworms (Dirofilaria immitis) starts when a mosquito bites an infected animal. As the mosquito feeds on the animal's blood, it ingests the microfilariae which are the immature form of the heartworm. Inside the mosquito the microfilariae develop into larvae. Then, when the mosquito bites an uninfected pet, the larvae are transmitted into that animal's bloodstream.
The larvae migrate through the pet's body to the heart where they develop into mature worms and reproduce. Heartworms commonly live in the right side of a pet's heart and can grow up to 12 inches in length. Infestation with heartworm causes cardiovascular disease in dogs and cats.
Although the parasite is more common in dogs, heartworm infection in a feline can be just as deadly. Research indicates that cats may have the potential for a more severe reaction to heartworms than dogs.
Occasionally an affected cat will show no signs of disease but others experience acute respiratory distress and can even die suddenly. The usual symptoms shown by an infected cat include coughing, difficulty breathing, exercise intolerance, fainting, lethargy, weight loss or vomiting.
Since these symptoms also can be caused by other diseases, a heartworm-infected cat can often be misdiagnosed. Cats may have 25 or fewer worms present when infected. Because of this, heartworms may be difficult to detect in a cat. Testing for both antigens and antibodies to heartworms is advised in felines.
Veterinarians may recommend chest x-rays for cats suspected of having heartworms. A positive radiograph shows enlargement of the right side of the heart as well as possible damage to portions of the lungs. Blood tests may show slightly elevated levels of eosinophiles (a type of white blood cell that is normally present when the body fights infestation by parasites).
For cats that do have heartworm disease, there is currently no approved treatment. However, because of the lower numbers for worms typically present in cats, a spontaneous cure can occur so that no treatment is necessary.
Some cats may experience ''crises'' such as elevated blood pressure, allergic-type reactions or even shock, when a worm dies. These symptoms can respond to the use of corticosteroids. Affected cats should also have their physical activity restricted.
A monthly preventative for feline heartworm is available through veterinarians. In endemic areas, such prevention may be the best remedy. Because indoor cats can have less resistance to such pests, a preventive may be more important for them.
There are currently four different preventatives available for cats. Two of these products are oral and two for topical application. All are administered once monthly. The American Veterinary Medical Association recommends asking your veterinarian to help you decide if your cat should be placed on heartworm preventative.
Additional information on Feline Heartworm Disease can be found on the American Heartworm Society website.
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