Fact or fiction—heartworm prevention should be given all year?

 

FACT – Yes, it’s true…you should still be giving your pet heartworm prevention through the winter months.  There are several reasons why year round prevention is recommended…

  Virginia has mild weather (especially in the winter).  Heartworm infection is spread from animal to animal by mosquitoes.  How many times have you found a mosquito inside your house in the winter?  Dogs, cats, ferrets, coyotes, foxes, wolves, sea lions and even humans have all been found to be infected by heartworm.  Adult female heartworms release their young (microfilariae) into the animal’s bloodstream.  Mosquitoes then become infected with microfilariae which mature into the infective larval stage within the mosquito.  When the mosquito bites another dog, cat or other susceptible animal, the infective larvae enter through the bite wound.  In dogs, it takes a little over 6 months for the infective larvae to mature into adult worms.  The adults can live for 5-7 years in dogs.  In cats, it takes about 8 months for the larvae to mature into adult worms that can live for 2-3 years.  Microfilariae cannot mature into adult worms without first passing through a mosquito.

Heartworm medication works by “back killing” instead of actually preventing future infestation.  “Back killing” means the heartworm preventative works to get rid of potential heartworm disease that may have been transmitted in the last 30 days but will not have any effect on the larvae introduced tomorrow.   There are several products used to prevent heartworm disease.  Each product works differently and may target different stages of the heartworm lifecycle.  Treatment for heartworm disease is expensive and can have side effects.  Therefore, it is much easier to administer a monthly preventative. 

Most heartworm prevention will also prevent against some common intestinal parasites which are infective all year.  Some of these parasites are potentially zoonotic (transmissible to people).  Therefore, you’re also benefiting by administering your pet monthly heartworm prevention year round.

It is important to use year-round heartworm prevention in cats as well. Cats can also get heartworm disease with prevalence in Virginia of 6-10%. And of these heartworm positive cats, 25% are indoor only. Heartworm disease isn’t quite the same in cats as most damage occurs in the lungs.

Common signs of heartworm infection range from no symptoms at all to coughing, exercise intolerance, difficulty breathing, lethargy, decreased appetite..