If I had a dollar for every time… There are several questions that we as veterinarians hear over and over. Most of the time this means that it is a good question and there’s a lot of people that need to know the answer. This will be the first in a series of posts in which we will take the time to answer these common questions.


If I had a dollar for every time someone asked me “Does my dog need to be on heart worm prevention all year round?”….


The answer to this question has changed over the last several years so I will explain the reasons that we recommend year round heartworm prevention. But first, let’s do a very quick review on heartworm disease and prevention. One disclaimer – this post will only address heartworm disease and prevention in dogs. There will be a future post on heartworm disease in cats so stay tuned.


Heartworm Basics courtesy of:  The American Heartworm Society

Heartworm disease is caused by worms that can be up to a foot long and live in the heart, lungs, and blood vessels. They can live for 5-7 years in the dog and cause severe damage to the heart, lungs, and blood vessels which can lead to lung disease, heart failure, and other organ failure. Adult female heart worms live in dogs, coyotes, and wolves. They produce microfilaria (immature worms) that circulate in the blood. A mosquitoes bites and takes blood including the microfilaria. Then the microfilaria developed into an infective stage of larvae in the mosquito, the mosquito bites the next animal and infects them. It takes 6-7 months from the time of infection until the heart worm is mature. Our heart worm tests detect a substance in the blood of a dog that is produced an adult female heart worm. So, it takes 6-7 months from the time the dog is infected until the test is positive. Most dogs don’t show any symptoms in the early stages of disease. As the heartworm infection progresses, symptoms include coughing, fatigue, weakness, decreased appetite, and weight loss. It can be fatal if left untreated. Treatment is expensive and dangerous so prevention is the key! Thankfully, heartworm disease is easily prevented by monthly preventives that you can give at home or injections given every 6 months. These preventives work by killing the immature stages (larvae) after a pet has been infected by a mosquito bite. They are very good at killing the larvae before they can mature into adult heartworms and cause disease.


Ok, so now that we’ve reviewed the basics of heartworm disease and prevention, let’s address the question “Does my dog really need to be on heartworm prevention year round?.


The simple answer to this question is a resounding YES!


Let’s dive into the top 3 reasons why your dog needs heartworm prevention all year round.


  1. Unpredictable weather

            Since heart worms are spread by mosquitoes, in the past we’ve always thought of it as a warm weather disease so we recommended using prevention spring through fall. However, our weather has become a bit more unpredictable so it’s not unusual to have warm days throughout late fall, winter, or early spring. The safest thing to do is keep your pet on prevention all year round so you’re ready for any warm days or unexpected mosquitoes.


  1. Tricky mosquitoes

            Species of mosquitoes are constantly adapting and changing to adjust to colder climates. Some can even survive the winter indoors! Also, new studies have found that some larvae are requiring three doses of heart worm prevention to be killed and successfully prevented from maturing to adult heartworms. So, you need to give 3 months of prevention after a few good, hard frosts. In Iowa, that means giving prevention year round.


  1. Intestinal parasite prevention

            Most heartworm preventives also include medications to kill common intestinal parasites such as round worms and hook worms. These types of worms can transmit to people. Round worms can travel to the eyes or internal organs of people to cause blindness or organ dysfunction. Kids, seniors and immune compromised people of any age are most at risk. The Companion Animal Parasite Council (CAPC) recommend administering year round broad-spectrum parasite control.


If you have any questions about heartworms or if you want to get your dog started on heartworm prevention, contact us today to make an appointment for a heartworm test.   Don’t leave your pet unprotected from this devastating disease!