Heartworm Disease

Heartworm disease is a potentially fatal disease of dogs, cats and ferrets.  Heartworms are a BLOOD parasite transmitted by mosquitoes.  Heartworms are NOT INTESTINAL parasites. Here are the basics of heartworm disease:

A mosquito bites a heartworm positive dog and ingests microfilaria (immature or baby heartworms) that live in the bloodstream.  That mosquito bites another dog and injects the microfilaria into that dog.  The microfilaria then go through several larval stages as they grow into 6-12 inch long adult worms that attach to the inside of the heart.  This process of larval development can take 6-8 months.  Can you imagine several 6-12 inch long worms in your heart?  YUCK!  As the number of adult worms increases, so does the damage done to the heart and pulmonary vasculature (blood supply to the lungs).  Congestive heart failure or pulmonary embolism may develop and can lead to death.

Dogs are the natural host for heartworms, meaning heartworms thrive in a dog's system.  Cats, ferrets and even humans are aberrant hosts, which means microfilaria can live in these species, but do not thrive.  Microfilaria and adult heartworms in aberrant hosts can cause plenty of trouble from asthma-like symptoms, to loss of vision, to sudden death.

Heartworm preventatives work by killing microfilaria – before they become adults.  It is VERY important to administer heartworm preventative the same day EVERY MONTH, ALL YEAR LONG.  Mississippi is home to many mosquitoes.  Mosquitoes do not die out unless they are exposed to 30 consecutive days of freezing temperatures-it does not freeze for 30 consecutive days in Mississippi.  Since mosquitoes are the method of transmission for heartworms, continuous protection is the best method of preventing heartworms in your pet!

The American Heartworm Society states "Annual testing is necessary, even when dogs are on heartworm prevention year-round, to ensure the prevention program is working.  Heartworm medications are highly effective, but dogs can still become infected. No preventatives are 100% effective. If you miss just one dose of a monthly medication, or your dog spits it out, or if you give it late, you are leaving your pet unprotected. If you don't get your dog tested, you won't know your dog needs treatment."  The longer a dog is heartworm positive, the more irreversible damage is done to the heart and blood vessels.  The longer a dog is heartworm positive, the harder it is to kill the adult heartworms.

There are many forms of heartworm prevention out there – however, they are all prescription.  There are NO heartworm preventatives sold over the counter.  Do not be fooled into thinking your dog is protected if you are buying "wormer" at the feed store.  You must purchase heartworm preventatives from your veterinarian or with a prescription from your veterinarian.  Many online pharmacies will fax or call in prescription requests to your veterinarian if you order from them.  Beware that many manufacturers do NOT guarantee products purchased through online pharmacies, as they do not sell directly to the online pharmacies.  If you have questions about which heartworm preventative is the best for your pet, please consult your veterinarian – they are your best resource!

See your veterinarian or the American Heartworm Society website for additional information:



Stay Happy, Stay Healthy,

Dr. Daisy


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