The Scourge of Heartworms

Four Lakes Veterinary Clinic

The scourge of heartworms is very prevalent in the southern United States.  When I practiced in Durham, NC, it was common to see 15-20 dogs diagnosed with heartworms in a year, if not more.  You would think more dogs in the South would be on heartworm preventative, but sadly that isn't the case.  There are a lot of dogs that never go to the vet and are reservoirs of microfilaria for mosquitoes to suck up and then inject into the next dog.


So what, exactly, are heartworms?  They aren't intestinal worms, like roundworms or hookworms.  Those worms are found in the intestines and the eggs can be detected in a poop sample.  Intestinal worms are easy to treat and eradicate from your dog (or cat).  But heartworms have a more complex life cycle, starting with a blood meal by a mosquito from an infected dog.


Adult female heartworms living in an infected dog, fox, coyote, or wolf produce microfilaria, microscopic "baby heartworms" that circulate in the bloodstream. When a mosquito bites and takes a blood meal from an infected animal, it picks up these microfilaria, which grow into an “infective stage” larvae in the mosquitoes gut over a period of 10 to 14 days. When the infected mosquito bites another dog, cat, or susceptible wild animal, the infective larvae are deposited onto the surface of the animal's skin and enter the new host through the mosquito’s bite wound. Once inside a new host, the larvae continues to grow and develop into a mature heartworm.  This takes approximately 6 months. Once mature, heartworms can live for 5 to 7 years in a dog's  heart and up to 2 or 3 years in cats. An infected pet can get infected over and over; having heartworms doesn't provide any immunity to getting more.


The highest incidence of heartworm disease is obviously in states where mosquitoes are a pain for much of the year--warm, moist climates, such as Texas, Tennessee, Alabama, North & South Carolina, and Florida.  You wouldn't think that Wisconsin has many heartworm positive dogs, and we don't, at least not compared to the southern states.  But, Madison brings up a lot of rescue dogs from down south, most of them just found as strays.  The chance of one of these dogs having heartworms is very high. 


Rescue dogs are almost always tested for heartworms before they are adopted out.  But it takes about 6 months before we can detect the adult worm in the heart.  So unless your veterinarian is retesting your adopted rescue dog 6 months after adoption, there is a good chance a dog with heartworms is getting missed.  That means any mosquitoes that bite that dog will be infected with the heartworm larvae and can pass the disease on to your dog.


So what should you do?

1. If you adopt a rescue dog, be sure to have your vet run a heartworm test 6 months after the dog was first tested.  Heartworm testing only requires 3 drops of blood and the results are generally back within 10 minutes.


2. Keep your dog on heartworm preventative year-round.  While we are unlikely to have many mosquitoes in the cold months, they can overwinter in your house.  And with global warming, our winters aren't as cold as they once were.  When the temperature reaches 50F, mosquitoes will be active.  Plus, heartworm preventative controls intestinal worms, which can be picked up year-round.


3. Have your dog tested for heartworms every year, even if they are on preventative year-round.  Your dog might spit a dose out, not absorb it properly (pill or topical), or you might have been late giving the medication one month.  (Many vets now test for tick-borne diseases, along with heartworms.  So you get a lot of information from those 3 drops of blood!)


Four Lakes Veterinary Clinic now offers both Heartgard, a monthly chewable, and Proheart 6, an injectable heartworm medication that takes a lot of worry out of heartworm prevention.  One Proheart 6 injection lasts 6 months, at which time you bring your dog in for another quick "poke."  No worries about missing or being late with a dose.  No worries about poor absorption or vomiting up a pill.  It is the solution I use for my collie, Scout, and I used it with my first dog, Chase, when I lived in North Carolina. 


If you have questions about heartworms or which preventative is best for your dog, please give us a call!



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