Heartworms
Everything you need to know about heartworms and how you can protect your pet.
Heartworms may sound like monsters in a science fiction film, but they are very real. Heartworms have been diagnosed in dogs across all 50 states in the U.S. and they plague many other areas of the globe as well. Your veterinarian or friends with pets may have warned you about heartworms, but it’s hard to defend your pets against something you can’t see if you don’t understand how it works.
Let’s get to the heart of this issue by discussing all of the key points you need to understand about heartworms in order to keep your pets safe!
What are heartworms?
Most people never see heartworms, and that may be a blessing since they are not pretty. These parasites go through a number of phases in their life cycle, but the adult stage is the only one visible without a microscope. Adult heartworms look like long thin noodles, with a single adult worm sometimes measuring up to 12 inches in length.
The average worm burden in an infected dog is 15 worms, but it can be as many as 300. All of those worms reside inside of the heart and they may spread to other organs through the circulatory system. Adult heartworms can live for 5 years while they continuously reproduce, and their scientific name is Dirofilaria immitis.
Lucky for us, heartworms are not a threat to humans since we are not a natural host for them. Sadly, we do not share that immunity with our pets. Dogs are a common host for heartworms, but cats, ferrets, and even certain wild mammals can also be affected by this parasite.
Where do heartworms come from?
It may seem impossible for a 12-inch worm to make its way into your pet’s heart without you noticing, but heartworms have a clever life cycle that keeps them out of view. These parasites rely on mosquitos as an intermediate host and prefer dogs as their main host.
Adult heartworms reside in a host’s heart where they reproduce. This results in their offspring, known as microfilaria, circulating in a host’s blood. When the host is bitten by a female mosquito, the microfilaria are ingested with the blood. They continue to develop into infective larvae while inside of the mosquito and are transmitted to the mosquito’s next victim.
If the host is suitable, the infective larvae move to the heart where they mature over the course of 5 to 7 months. Then they reproduce and the cycle continues all without you or your pet ever seeing a worm.
Please note that this means heartworm is not transferred directly from pet to pet, a mosquito must be involved as the intermediate host.
What pets are at risk of getting heartworms?
Currently, 30 species of mosquitos are known to transmit heartworm and the parasite has been documented in mosquito-prone areas across the globe. Such a small, widespread, and stealthy vector means that virtually no dog can be guaranteed immunity from heartworms if they live in an area with mosquitos.
Have you ever gotten a mosquito bite while indoors? Chances are, your pet has too. Even if a dog spends a majority of their time indoors or a cat spends all of their time indoors, they are still at risk.
Dogs, cats, and ferrets are the main pets at risk of being infected with heartworm. Wild canids, felids, raccoons, and other wildlife can also be infected. This further contributes to the circulation of infectious larvae in mosquitos and the spread of heartworm on a global scale.
What are the impacts of heartworms?
As you can imagine, a heart full of worms is not easy to live with. When the amount of adult worms in a dog is low, there may be few to no notable symptoms. As that population grows, the heart becomes congested and other organs may be affected as well. It can take several years for symptoms to develop in some cases.
Heartworms are a burden on any affected animal, and they will not resolve on their own. Symptoms are most apparent when worm burdens are high, an animal is older, or an animal is already sick. These symptoms can include:
● Cough
● Fainting
● Nose bleeds
● Lethargy
● Loss of appetite
● Difficulty breathing
● Rapid exhaustion from exercise that your pet could normally handle
● Cats may also display vomiting
● Organ damage due to restricted blood flow
If untreated, these symptoms can progress and lead to death. In some cases, cats can experience sudden death with few symptoms.
Is there treatment for heartworm infections?
If a dog is already infected with heartworms, treatment is possible. The most popular treatment is called Immiticide® and it is injected in phases to kill off adult heartworms. Another medication is required to kill off the microfilariae and other treatments may also be necessary depending on each dog’s specific circumstances. It takes time for this medication to work, it is not without risks, and dogs need to be minimally active after these treatments are administered.
Treatment can kill off the worms infecting your dog, but it can not undo any damage that has already happened to vital organs. It is also worth noting that dogs who have been treated for heartworm infections in the past can be reinfected in the future if they are not protected.
Our feline friends do not fare so well when it comes to heartworm treatments. Currently, there is no known safe medication for heartworm treatment in infected cats. A veterinarian may offer medication to help with symptoms, but there is no reliable cure. Surgery is another option, but it is generally considered to only be viable if heartworms can be seen by ultrasound, and even then there is a risk of death.
How can I protect my pet against heartworms?
The good news is heartworm disease can be prevented. Pets that have not been infected yet can take preventive medication that kills off the microfilaria before they develop, effectively stopping adult worms from forming and causing damage.
This treatment should only be dispensed by a registered veterinarian who has tested your pet for heartworm. Testing is important because preventatives can be dangerous if they are administered to a pet who is already infected with heartworm. These preventatives come in multiple forms and should be administered all year for maximum protection.
- Injectable Preventatives
These are administered by your veterinarian and are generally given in 6-month intervals. - Topical Preventatives
These are applied to your dog or cat’s skin at home, and they may help to protect against other parasites like fleas or ticks depending on the brand. - Oral Preventatives
These are consumed by your pet and can be administered at home. Some even look and taste like dog treats!
Be sure to discuss preventatives with your vet so you can choose one that is best suited to your pet’s needs. Preventatives also require that your pet is checked for heartworms yearly, and they may require more frequent testing if they come off of preventatives for a period of time.
Your veterinarian can provide you with lifesaving advice for your pet, so never hesitate to discuss any questions or concerns you may have regarding heartworm. Being well informed and taking action can save your pet’s heart from this deadly parasite.
Citations:
- https://www.heartwormsociety.org/veterinary-resources/american-heartworm-society-guidelines
- https://www.aspcapetinsurance.com/resources/heartworm-symptoms-and-treatment/
- https://vcahospitals.com/know-your-pet/heartworm-disease-in-dogs
- https://www.avma.org/resources-tools/pet-owners/petcare/heartworm-disease
- https://www.fda.gov/animal-veterinary/animal-health-literacy/keep-worms-out-your-pets-heart-facts-about-heartworm-disease