“Cats are not little dogs.” This axiom is taught in veterinary school early and often. It is clearly evident in how heartworm disease affects these two species. In cats, the reaction to infestation with this worm is so different that it is given another name entirely: Feline Heartworm Associated Respiratory Disease (Feline HARD).
Cats are infected (like dogs, humans, ferrets, et al.) by mosquitoes carrying the larvae of the insect Dirofilaria immitis. The larvae are transferred into the skin and into the bloodstream where they grow through their different stages until they become adults, lodging and living in the chest – the heart chambers and associated arteries and veins (vena cava, pulmonary artery, pulmonary vein, etc.).
In the dog, symptoms usually occur after the worms develop into adults and mate, shedding larvae into the bloodstream, and when so many adults crowd into the arteries, veins, and chambers that they physically obstruct blood flow. In the cat, as the larvae circulate and grow, there is often such severe reaction by their lungs that cats appear to have “asthma” attacks, severe coughing problems, and associated symptoms like fevers, aches all over, poor appetite, hiding, etc. Also, in cats it is not uncommon for only 1 or a very few worms to develop to adulthood. This can lead to not finding any larvae when testing for heartworm (only males present, or only 1 female present) and therefore needing different tests than for dogs.
So if your cat has exposure to mosquitoes (even inside; my house screens are not perfect), signs of asthma, coughing or not doing well in general, a trip to your veterinarian should be planned for blood tests to look for both antigen (proteins from the worms) and antibodies (reactive cells that try to isolate/kill foreign entities). A complete physical exam and chest radiographs (x-ray pictures) likely will also be needed.
An even better idea to consider is to prevent parasites in your feline friends with a treatment like feline Revolution (selamectin). This treatment prevents development of the heartworm larvae if introduced into the cat, kills off any exposure to roundworms, hookworms, fleas, and ticks (also some other parasites like walking dandruff, some lice and mites). Give us a call to discuss any questions you may have about feline HARD.