Parasites can be a sneaky threat to your pet’s health, and heartworms top the list of dangers. Heartworm transmission occurs via a mosquito bite, so all pets are at risk for infection, which can be serious and life-threatening. Thankfully, with a little help from your veterinarian, heartworm disease can be easily prevented. April is National Heartworm Awareness Month, so your Pierson Pet Hospital team would like to answer your frequently asked questions about heartworm disease, to ensure you can keep your pet safe.
Question: What are heartworms?
Answer: Heartworms are specialized parasitic worms that live in the blood vessels and chambers of the heart and lungs of dogs, coyotes, foxes, and wolves. In these hosts, they can reproduce, and sometimes reach numbers in the hundreds. Other mammals, such as cats, are considered “dead-end” hosts—the worms can infect them, but most don’t reach maturity and cannot reproduce, so these hosts have only a few worms at a time.
Q: How do pets get heartworms?
A: Pets and wildlife with heartworm disease serve as an infection reservoir, but they don’t infect other pets directly. Tiny immature worms (i.e., microfilariae) circulate in their blood, which are picked up by mosquitoes as they feed. The microfilariae mature inside the mosquito for about two weeks, and are transferred to another host when the mosquito bites again. Once inside the new host, the immature worms travel for about six months through tissues to the lungs, where they mature to adults. If the host is suitable, as with dogs, the adults then reproduce, and the cycle starts over again. In cats, many microfilariae are likely to die, but some may survive to adulthood and produce a problematic infection.
Q: How do heartworms affect dogs?
A: Heartworms thrive in dogs, who tend to harbor large worm burdens from 30 to several hundred at a time. The worms can live up to seven years in dogs, so the number of adult worms will increase the longer infection goes undetected. Heartworms can permanently damage the structure of the heart and lung blood vessels, and cause inflammation. Dogs with heartworms may develop:
- Exercise intolerance
- Coughing or trouble breathing
- Heart failure
- Fluid accumulation in the abdomen (i.e., ascites)
- Weight loss or decreased appetite
- Sudden collapse or death from caval syndrome (i.e., heart arteries physically blocked with worms)
Q: How do heartworms affect cats?
A: Cats are “dead-end” hosts, so typically only one to six worms reach adulthood. Heartworms that manage to infect cats cause significant lung damage and inflammation, which can mimic asthma or bronchitis, but has its own term (i.e., heartworm associated respiratory disease [HARD]). They can also cause heart damage or failure and, unfortunately, the first disease indication in some cats may be sudden death. Others may develop chronic problems, including:
- Coughing or wheezing
- Panting or labored breathing
- Vomiting and weight loss
- Collapse or sudden death
Q: How is heartworm treated in dogs?
A: Dogs are treated with a series of painful injections that go deep into their spinal muscles and kill the adult worms. Dying worms can cause clots or anaphylactic reactions, so most dogs are also given antibiotic and steroid medications and kept severely activity-restricted for several months, to prevent these complications. Heartworm-positive dogs are also placed on monthly preventive products that kill microfilariae.
Q: How is heartworm infection treated in cats?
A: Unfortunately, cats cannot be treated directly for heartworm disease, since the drug that kills adult worms isn’t safe for cats. Heartworm-positive cats must be treated symptomatically and supportively during the worms’ two- to three-year lifespan, and monitored with imaging and blood tests. Medications can help with inflammation and to support heart and lung function, but some cats do not survive infection. Heartworm-positive cats are started on monthly preventives to keep them from acquiring new heartworms.
Q: Can heartworms be prevented in pets?
A: Yes! Heartworms can be deadly in dogs and cats, and usually cause significant damage by the time disease signs are evident. Prevention is a far easier, safer, and more affordable alternative. Heartworm prevention products come in many formulations, including oral and topical, are administered monthly, and work by killing newly acquired microfilariae before they mature into adults. Heartworm prevention is recommended year-round for all pets, including those who live indoors, as mosquitoes can easily come inside through screens and cracks. Our Pierson Pet Hospital veterinarian can recommend a heartworm prevention product that is right for you and your pet.
Q: Should my pet be tested for heartworms?
A: For dogs, heartworms can be detected on a simple blood test, but only if adult worms are present. Testing cats is more complex, since only one worm may be present, and the blood test looks for evidence of adults, as well as the body’s antibody response, so other confirmatory tests or imaging may be required. Dogs and cats should be tested prior to starting preventives. Since worms take around six to seven months to mature into adults, pets younger than 7 months don’t need a test prior to starting a preventive, but should be tested at their first annual adult visit. Adult dogs should be tested yearly if they are on preventive regularly, or every six months if they have recently started, or had a break in prevention. Our veterinarian can recommend the best testing schedule for your pet.
The tiny pests that transmit heartworms can have a big impact on your pet’s health. If heartworm hasn’t been on your radar, now is a great time to make prevention a priority. Contact us to schedule an appointment with your Pierson Pet Hospital team for your pet’s next wellness exam and heartworm test, or if you have questions about heartworm disease, prevention, or testing schedules.