It takes about two months for the worms in cats to migrate through the connective tissue under the skin to get into the arteries of the lung. In total, it takes seven to eight or so months for the larvae to mature into adult worms that then begin producing their very own offspring (small worms / microfilariae).
The good news is that cats are not really good hosts for Heartworms since the adult worms can produce offspring in only about 20% of the cats and of these few make it to adulthood.
Also, unlike dogs, dogs that may suffer from Heartworm-induced heart and lung damage cats show only minimal adverse effect in the heart. Instead cats often show symptoms in the lungs.
FELINE HEARTWORM SYMPTOMS
It is nearly impossible to determine whether your cat has Heartworm by clinical signs alone. However, the generic signs of illness (applicable to many illnesses) are vomiting intermittently (food or foam, usually unrelated to eating), lethargy, loss of appetite / weight loss, coughing, asthma, rapid breathing (tachypnea) or gagging.
A Heartworm infection can also result in acute pulmonary inflammation response and lung injury. Signs associated with Stage 1 Heartworm disease (when the heartworms enter a blood vessel and are carried to the pulmonary arteries) are often wrongly diagnosed as asthma or allergic bronchitis. In fact these symptoms are caused by what is now called heartworm Associated Respiratory Disease (HARD).
DETECTING HEARTWORM IN CATS
According to the Heartworm Society diagnosis can be done by a physical examination and the heartworm antibody test and the heartworm antigen test. The feline heartworm diagnosis is confirmed when BOTH antibody and antigen tests results are positive.
PREVENTING FELINE HEARTWORM
Since mosquitos are the main transmitter of the hearworm parasite, so to reduce your risk, reduce mosquitos. Mosquito Dunks work well by killing mosquito larvae before they become old enough to bite. All you need to is place the Dunks wherever there is standing water or standing water will accumulate since this is where mosquitos mature.
As for medicines to prevent heartowm in your cat or kitten, your best bet is to use heartworm preventives properly. Be aware that all approved heartworm medications work by eliminating the immature (larval) stages of the parasite, including the infective heartworm larvae deposited by mosquitos as well as the following larval stages. Unfortunately for your cat or kitten, immature heartworm larvae can evolve into the adult stage. Therefore, hearworms must be eliminated before they reach this stage of development. As a result, you must administer the heartworm preventives on schedule (monthly for oral and topical products and every 6 months for the injections).
TREATING HEARTWORM IN CATS
According to the Heartworm Society There are no products in the United States approved for the treatment of feline heartworm. In fact the most commonly recommended treatment for cats that display no overt clinical signs (despite being diagnosed with Heartworm) is to allow time for a spontaneous cure to occur. This is followed by regular checkups / testing every 6 to 12 months.
Where there are signs of lung disease your vet may recommend a therapy using use "small, gradually decreasing doses of prednisone (a cortisone-like drug).
Best bet in all circumstances is to discuss your cat's Heartworm with your vet as many times no treatment is needed. I hope this is of help to you. Simba