Heartworms (Dirofilaria Immitis)

Heartworm prevention is the single most important thing you can do to keep your pet healthy throughout its lifetime since any dog living in south Louisiana will be exposed to infected mosqitoes whether he lives indoors or out.  Whether the prevention you choose is given by injection, orally, or topically, all approved heartworm medications work by eliminating the parasite at the immature stages of the life cycle.  A mosquito gets infected with heartworm L1 larvae when it takes a blood meal from a dog that is infected with heartworms.  The larvae molt twice inside the mosquito to become L3 larvae which can then can infect your dog or cat when that mosquito feeds on your pet and passes on those larvae.  These larvae grow, develop, and over time migrate to the heart and great vessels where they eventually become adults. These adult heartworms begin to produce their own microfilaria about 6 to 7 months after your pet is first infected and the cycle begins again.  The worms which reach four to twelve  inches (females are longer than males) become fully grown about one year after infecting your pet.  Their life span in dogs appears to average four to six years.  In cats these heartworms usually won't reproduce but can cause great harm to your pet's heart and lungs often resulting in the sudden death of your cat.

 

Testing:

The  American Heartworm Society recommends testing  ALL dogs annually, even those patients who have been on consecutive monthly preventative (given orally every 30 days) or  the injectable preventative given once every six months.  A negative test is needed to begin any heartworm preventative for patients 6 months of age or older. 

Manufacturer’s Guarantee:  

Each company stands by the efficacy of its product and has its own protocol for coverage when starting preventative or switching from one preventative to another. 

 Switching Preventative:

Switching a patient to a different preventative requires heartworm testing to rule out existing infection.  Results are good for 30 days.

Proheart- To be covered, dogs must test negative for adult heartworms and microfilaria when starting Proheart, even if they are up-to-date on another preventative.  They must then test negative again in 6 months.  Dogs can begin Proheart at 6 months of age.

Heartguard- To be covered, dogs 4-6 months of age need to be tested 6 months after starting Heartguard to rule out existing infection.  Dogs 6 months or older need to test negative for adult heartworms and microfilaria to begin preventative then test negative again in 6 months. Dogs can begin Heartguard at 6 weeks of age.    

Trifexis- To be covered, dogs 4-6 months of age starting on Trifexis need to be tested in four months to rule out existing infection.  Dogs 6 months or older need to test negative for adult heartworms and microfilaria when beginning Trifexis even if they are up-to-date on preventative and then test negative 4 months later.  Dogs can begin Trifexis at 8 weeks of age.

Advantage Multi- To be covered, dogs 4-6 months need to be tested 4 months after starting Advantage Multi to rule out existing infection.  Dogs 6 months or older need to test negative for adult heartworms and microfilaria when beginning Advantage Multi then test negative again in 4 months.  Dogs can begin Advantage Multi at 7 weeks of age. Cats can begin Advantage Multi at 9 weeks of age.

Nothing is Perfect:

It is easy to miss doses or fail to give the preventative on the same day every month.  Pets may vomit or spit out their dose of prevention.  Therefore preventatives are “nearly” perfect, but nothing is absolute.  If a patient is a day late on a dose of preventative they can test positive in the future.  To prevent a positive test, all chewable and topical preventatives can be given every 28 days.  Giving preventative to a patient with heartworms can cause a serious adverse reaction.  The danger of not testing is not knowing.  Therefore it is important to check with the doctor before giving any pet heartworm preventative.

 

Durocher Veterinary Clinic * 703 Jackson St * Thibodaux, LA 70301 * 447-8261