Cat Heartworm

Contrary to popular belief cats get heartworm too. It is true that this dangerous parasite is designed specifically to live part of its life inside a canine body. But if a mosquito passes heartworm larvae to a feline instead, many will survive, to cause the cat serious health problems.

More and more pet owners are now using preventative heartworm meds for their dogs. Sadly, not enough cat owners are doing the same so feline heartworm disease looks set to keep growing.

The reason so many of us do not use a heartworm preventative medicine for our cats is that until the last 20 years, the problem was thought to be very rare. However, it is now believed that a large percentage of cats diagnosed with problems such as feline asthma and bronchitis are actually suffering from heartworm disease.

As heartworm often do not breed in feline hosts, there are no microfilaria are produced. It is these heartworm offspring, found in the bloodstream, which most vets test for when looking into a possible heartworm infection. The parasites are much harder to test for in cats than dogs. Also the symptoms of an infestation in cats can be extremely varied and non-specific.  Some cats will survive heartworm disease and even fight off the infection themselves while others will die suddenly even if only one adult heartworm has reached the heart.

On average fewer cats receive full veterinary care offered to dogs.  This is not any-one's fault, there are just an awful lot of stray cats and partially feral cats around.  They may get fed but they do not get taken to a vet if poorly and they certainly do not get taken for an autopsy if they suddenly die.  All this means the rate of infection in cats is extremely difficult to fathom.

Estimates for the rate of feline heartworm disease run from 5-20% of the incidence of the disease in dogs in an area. But other studies believe the rate could be much higher from 40-50%.

One thing, all the health professionals and the Heartworm Society agree on, is that wherever dog heartworm disease is found, there will be cats infected too.  This makes feline heartworm prevention important in huge areas of the world.

There are several heartworm meds which can safely be used to stop your cat ever contracting heartworm in the first place. Before starting heartworm medicine your cat should be checked for heartworm disease by your vet. Giving a heartworm disease positive cat any heartworm preventatives can be hazardous to health.

There are four brands providing good heartworm prevention for cats:

• Heartgard^® which is given orally and uses Ivemectin as its active ingredient.
• Interceptor^® which is given orally and uses Milbemycin oxime as its active ingredient.
• Revolution^® which is given topically and uses Selemectin as its active ingredient.
• Advantage Multi™ which is given topically and uses both Moxidectin & imidacloprid as its active ingredients.

There are also several generic heartworm meds available which use the same volume of the active ingredient so are just as safe and effective but are cheaper to buy. Always ensure you choose a Cat Heartworm Preventative for the correct size of cat. Doses suitable for larger animals may contain potentially dangerous amounts of active insecticide while those designed for other animal species may contain ingredients particularly toxic to cats.

By giving a preventative tablet or spot on treatment, the active ingredients are absorbed into the cats bloodstream where they destroy all the larval heartworms picked up via mosquito bites during the 30 days since their last treatment.  Topical heartworm meds also provide effective cat flea treatment so reducing the number of pet meds you need to worry about.

Repeated timely treatment is critical throughout the active mosquito season as missing one treatment puts your cat at risk of being infected with the heartworm parasite.

Heartworm Preventative Medicine is an FDA controlled pet medication. In the United States a prescription is required from your veterinarian before any pet med store can dispatch heartworm preventatives to you.

The rules are slightly different in different countries. Many heartworm prevention medications such as Revolution, Advantage Multi and Heartgard are available without a prescription from sites such as The Pet Meds Info site.

The FDA would rather this practice stopped, and would like all heartworm medication coming into the United States to be sold with a prescription. We do not know how much longer the practice of being able to buy them from overseas is likely to continue.

The symptoms of heartworm disease in cats are very subtle and often non-specific.  The following are usual signs but they could also indicate some completely different health problem:

• Asthma - difficulty breathing, wheezing or gasping for air.
• Persistent cough.
• Lethargy.
• Loss of appetite.
• Unexplained weight-loss.
• Occasional difficulty walking.
• Vomiting.
• Seizures & fainting.
• Sudden death.
  

The drugs used to treat heartworm for dogs are too strong to be used in cats. 

At the moment their are no recognised drug therapies to treat cats infected with heartworm.  Very occasionally a vet will use a heartworm adulticide but only if all else fails.  Cats are much less able to absorb dead heartworm so killing the heartworms can be even more dangerous than the disease they cause. 

Luckily heartworm only tend to survive in cats for 2 to 3 years rather than 5 to 7 in dogs.  But still that is several years of worry and repeated vet bills for x rays, ultrasound scans and possible additional therapy to aid recover of lungs damaged by heartworms.  Plus, all the time the heartworms are inside your pet they are damaging organs and blood vessels.

Feline heartworm disease is less prevalent than canine heartworm disease.  But, cats do pick up the parasite wherever there are incidences of dogs with the disease.  Some cats fight off the infection themselves while others succumb to serious illness and many will be fatally affected.

Areas with high mosquito populations, such as close to river deltas and along the Gulf coast are more prone to the problem.  Year round active mosquitoes bring increased rates of heartworm disease.  But even in those states we think of as relatively dry and mosquito free there are reported cases of heartworm disease.  The mosquito population can vary hugely in a small area.

If the overall level of mosquitos is low in your region, make sure you keep them away from your own back yard too by not leaving containers around to collect stagnant water.

Looking at the Heartworm Society's studies regarding the incidence of heartworm disease from 2001 to 2004 we can see the problem is definitely becoming more widespread in terms of location, and more common in terms of numbers too.  So it may be safe to assume that even if we believe the threat of heartworm in our area is low it is likely to increase in the future.

Treatment for the disease in cats is virtually non-existent so if you are worried about your cat getting the disease you should use a preventative medicine.