About Heartworm Disease in Dogs

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[Dr. Jeff Werber:
Protecting your dog from parasites is one of the most important things you can do to help ensure long-term health for your pet. And heartworm disease is one of the most deadly threats your dog can face.

Heartworm disease is a serious problem. The American Heartworm Society estimates that over 1 million dogs currently have this potentially fatal disease*, and more cases are being diagnosed each year, many in parts of the country that are not normally known as hotbeds of heartworm. So let’s take a closer look at the heartworm lifecycle.

Heartworms are spread to dogs through the bite of an infected mosquito. Immature or juvenile heartworms, called larvae, enter the dog’s body at the site of the mosquito bite. They then pass through the dog’s tissue, enter the bloodstream and make their way to the heart.

Once in vessels near the heart, the larvae gradually develop into adult heartworms. The adult worms will cause the dog serious health problems. In severe infections, the worms disrupt heart function and blood flow, and can even damage the dog’s lungs, liver and kidneys. If left untreated, heartworm disease can be fatal.

As adult heartworms reproduce, they send more newborn heartworms into the bloodstream. At that point, if the infected dog is bitten by a mosquito, the disease may then be spread to other dogs. The time between the initial mosquito bite and a positive test result for heartworm disease is often more than six months, so unless you are continuously administering a monthly heartworm preventative, your dog could test negative, yet still develop heartworm disease.

Heartworm disease often doesn’t present with many symptoms, so it can be very difficult for pet owners to spot. When symptoms do appear in your dog, they can include coughing, fatigue and exercise intolerance. Unfortunately, by the time these symptoms appear, it’s usually a sign that significant damage has occurred. So what can you do to protect your dog? 

You can take steps to reduce your dog’s exposure to mosquitoes by eliminating standing water where mosquitoes breed. Cleaning gutters, emptying bird baths and outdoor pet bowls will all help a little, but it’s hard to eliminate mosquitoes. They can survive extreme temperatures and reappear when you least expect it. Fortunately, it’s easy to prevent heartworm disease. Simply have your veterinarian test your dog annually, and give heartworm prevention each month, all year-round.

Preventatives don’t kill adult heartworms. They kill the juvenile heartworms before they can grow and reproduce. That’s why it’s important that your veterinarian tests your dog for heartworms before starting a monthly preventative routine. A positive test result may be an indication that your dog requires more aggressive treatment. And serious health issues can occur in dogs with a pre-existing heartworm infection if they begin a heartworm preventative routine, so follow your veterinarian’s advice and have your dog tested for heartworms regularly.

To avoid the deadly effects of heartworm disease, your best bet is to start a monthly heartworm routine as soon as you can – and stick to it.

Ask about Trifexis, the combination product that kills fleas and prevents infestations, prevents heartworm disease, and treats and controls hookworm, roundworm and whipworm infections. See the full product label for complete safety information.

Serious adverse reactions have been reported following concomitant extra-label use of ivermectin with spinosad alone, one of the components of Trifexis. Treatment with fewer than three monthly doses after the last exposure to mosquitoes may not provide complete heartworm prevention. Prior to administration of Trifexis, dogs should be tested for existing heartworm infection. Use with caution in dogs with pre-existing epilepsy.

The most common adverse reactions reported are vomiting, depression, itching and decreased appetite. To ensure heartworm prevention, observe your dog for one hour after administration. If vomiting occurs within an hour of administration, redose.

*American Heartworm Society data; https://www.heartwormsociety.org/images/pdf/AHS_InfoGraphic.pdf. Accessed 5/2/17.]

PROTECT AGAINST HEARTWORM DISEASE IN DOGS

Protecting your dog from heartworm disease is easy with one Trifexis® (spinosad + milbemycin oxime) chewable tablet, once a month, year-round. Trifexis works by killing heartworm larvae after an infected mosquito bites your dog and before the larvae mature and become adult heartworms (D. immitis).

What is heartworm disease in dogs?

You may wonder, “How does a dog get heartworm disease?” Heartworm infection can be deadly, and it starts with the bite of an infected mosquito. From there, the worms penetrate the dog’s tissue, migrate to the bloodstream, and enter his heart and lungs.

Risks of heartworm disease

Heartworm disease symptoms in dogs can include1,2:

  • Coughing
  • Exercise intolerance
  • Difficulty breathing
  • Enlarged liver
  • Death

However, a dog with a heartworm infection may have no visible symptoms. Regardless, if left untreated, heartworm disease can be deadly.2 Your veterinarian should perform a yearly blood test, which is an important part of your dog’s routine health check, in order to detect a heartworm infection.

Heartworms can live in an infected dog for 5 to 7 years.1,2 In time, damage to your dog's heart and lungs can be severe and can include1,2:

  • Clogging and damage to the lining of the artery leading from the heart to the lungs 
  • Heart valve malfunction
  • Liver and kidney dysfunction
  • Heart failure

Heartworm incidence nationwide as of 2016

Heartworm incidence nationwide map

Map © American Heartworm Society: The severity of heartworm incidence as shown in this map is based on the average number of cases per reporting clinic. Some remote regions of the United States lack veterinary clinics, therefore we have no reported cases from these areas.

Year-round protection is essential

Your love for your dog knows no season, and neither should his heartworm protection. That’s why the Companion Animal Parasite Council and the American Heartworm Society recommend uninterrupted, year-round treatment with a broad-spectrum parasite control product without interruption, regardless of where you live.1,2

Why administer heartworm prevention year-round?

Heartworm larvae generally develop in temperatures above 57°F. However, colder temperatures can just pause the process and result in larval growth resuming when the air warms up.2 It’s just one more reason why year-round heartworm protection is important.

If your veterinarian prescribes less than year-round protection, it’s important to administer Trifexis for at least three months after your dog’s last exposure to mosquitoes. It can take up to six months or longer for the symptoms of heartworm disease to manifest in your dog, so it’s advisable to administer Trifexis monthly—even in winter or other times you don’t see mosquitoes. 

Life cycle for heartworm in dogs

Illustrated stages of heartworm infection
A dog with an active heartworm infection. Microscopic larvae (microfilariae) are produced by adult worms and circulate in the blood. Larvae appear in the dog’s blood about 6-9 months after infection.

A mosquito bites an infected dog and ingests blood containing microscopic heartworm larvae.

Microscopic larvae develop within the mosquito and enter the infective stage in about 2 weeks, under ideal conditions.

Infective larvae are contained in the saliva of the mosquito.

The infective larvae enter the bite wound from a mosquito and migrate into the tissue of the dog.

Larvae migrate through tissue and mature to enter the bloodstream, making their way to the dog’s heart and pulmonary arteries, about 70 days after infection.

Larvae develop into adult heartworms and reside in the pulmonary arteries. In heavy infections, adult worms may invade the chambers of the heart and cause symptoms including coughing, sluggishness and difficulty breathing, though some dogs may show no signs at all.

Adult heartworms produce microscopic larvae that are released into the bloodstream.

HEARTWORM PREVENTION for Dogs

View video transcript

[Dr. Jeff Werber:
When used as directed all year-round, heartworm preventatives are highly effective at protecting dogs against heartworm disease. Your veterinarian will need to regularly test your dog for heartworms as part of basic preventive health care. In some cases, your dog may test positive for heartworms even after starting a heartworm preventive routine. That doesn’t necessarily mean that the product you are using isn’t working. Let’s take a look at why.

Heartworm preventatives work by killing the youngest juvenile-stage worms after the mosquito bite. As the worms mature, they become less likely to be killed by the medication. So if your dog was already infected before starting a monthly heartworm routine, those existing adult heartworms may eventually trigger positive test results.

Also, if your veterinarian has previously treated your dog for heartworm disease, you might be surprised to learn that it can take more than a year for your dog’s body to remove all the evidence of an infection from the bloodstream. And to make matters even more complicated, heartworm disease doesn’t show up in tests until five to nine months after your dog was bitten by an infected mosquito. So a “negative” test result is not a guarantee that your dog is free of heartworm infection. It simply means that the tests did not detect the presence of heartworms in your dog.

Your dog could miss a dose of her monthly heartworm preventative, spit out or vomit the tablet without you realizing it, or be on the wrong dosage based on her weight. These could all cause a positive test result at some point in the future. Bottom line? It’s important to test your dog for heartworms regularly – especially prior to starting a new heartworm preventative.

Serious health issues can occur in dogs with a pre-existing heartworm infection if they begin to take a routine heartworm preventative. Your best bet is to start a heartworm preventative as soon as you can – and stick to it. If you still have questions about your dog’s test results or treatment program, talk to your veterinarian. 

Ask about Trifexis, the 3-in-1 combination product that kills fleas and prevents infestations, prevents heartworm disease, and treats and controls hookworm, roundworm and whipworm infections. See the full product label for complete safety information.

Serious adverse reactions have been reported following concomitant extra-label use of ivermectin with spinosad alone, one of the components of Trifexis. Treatment with fewer than three monthly doses after the last exposure to mosquitoes may not provide complete heartworm prevention. Prior to administration of Trifexis, dogs should be tested for existing heartworm infection. Use with caution in dogs with pre-existing epilepsy.

The most common adverse reactions reported are vomiting, depression, itching and decreased appetite. To ensure heartworm prevention, observe your dog for one hour after administration. If vomiting occurs within an hour of administration, redose.]

When it comes to protecting your dog from heartworms, prevention is your best weapon. That’s because treating an infected dog can be painful, expensive and may not be 100% effective.2 Plus, your dog could have serious health complications.

Two key steps to keep your dog from developing heartworm disease:

1) Annual testing

Consult your veterinarian about testing your dog annually for heartworm infection. If a test is positive, your veterinarian will discuss your treatment options.

2) Year-round protection

Provide your dog with year-round heartworm prevention with Trifexis. It makes heartworm prevention as easy as one chewable tablet, once a month, year round. If your veterinarian prescribes less than year-round prevention, it’s important to administer Trifexis each month for at least three months after your dog's last exposure to mosquitoes.

See how Trifexis can stop this deadly heartworm cycle.

Learn more about Trifexis