Not for the Faint of Heart: Heartworm Disease and Prevention
Heartworm disease has long been a known problem that affects dogs, and recently it is becoming apparent that cats are infected with heartworm more frequently than originally thought. In fact, it has been reported that up to 15% of cats in some areas are now testing positive for this disease.
In the U.S., heartworm disease was once limited to the south and southeast regions, but, for a number of reasons, it is now found in all 50 states. Conrad Weiser Animal Hospital thought it an opportune time to bring you the facts about heartworm prevention.
What Causes Heartworm?
Pets contract heartworm from feeding mosquitoes. The heartworm life cycle is long and complex, and requires two host animals to complete. The steps for infection are:
- A mosquito bites and takes a blood meal from an infected animal (cat, dog, or wild animal).
- Next, the baby heartworms, or microfilariae, develop further inside the mosquito’s body over the course of 10-30 days.
- The mosquito bites a dog or cat, transmitting the microfilariae to the bloodstream. The microfilariae develop further over the course of months, finally finding their way to the pet’s heart and blood vessels, where they mature into foot-long adult heartworms.
- About 7 months after the pet is infected, the adult heartworms are capable of reproduction and release new microfilariae back into the bloodstream. The pet becomes a new host, able to pass infection to another pet through a mosquito bite.
Any pet that is exposed to mosquitoes is at risk for heartworm disease. And, let’s be honest, even with the best screen doors, mosquitos do come inside! So, even indoor cats and dogs can contract the disease, although they are less susceptible to it than outdoor pets. We’ve also noticed a longer warm season, making mosquitoes prevalent for much of the year.
It is important to note that many wild animal species, such as wolves, coyotes, and foxes, are significant carriers of the disease. The incidence and risk of heartworm may be greater in areas where these wild species are present.
Another challenge that we face with the spread of the disease is that pets who are rescued from Gulf Coast areas that are endemic for heartworm are sometimes adopted to other areas of the country. This kind- hearted act can bring heartworm disease into areas that might not have been affected previously. We saw this with the Hurricane Katrina and Rita disasters, when dogs that were rescued were dispersed around the country. It was later reported that up to 60% of the rescued dogs were infected with heartworm.
Signs and Diagnosis
The signs of heartworm can be subtle, but they can be extreme as well.
Signs may include:
- Difficulty breathing
- Sudden onset coughing
- Rapid breathing
- Weight loss
- Respiratory distress
- Sudden death (cats)
Diagnosis is more elusive in the cat, which is considered a resistant host. Tests performed to diagnose heartworm may include:
- Heartworm antigen blood test
- Heartworm antibody blood test
- Chest X-rays
- Echocardiogram or cardiac ultrasound
Can Heartworm Be Treated?
Heartworm in dogs can be treated, but there is currently not an approved drug for the treatment of heartworm in cats. When we diagnose heartworm in dogs, a series of injections is given over the course of months to kill the worms. In cats, there are only two (not very good) options. Treat the cat with the dog-approved drug and take the risk of the cat dying suddenly, or treat the symptoms which can include acute respiratory distress.
Prevention: Your Best Defense Is a Good Offense
In a nutshell, treatment in dogs is expensive and recovery is tedious, and there are no good options for treatment in the cat. Luckily, heartworm prevention is easy, safe, and effective. At your pet’s next wellness exam, we can prescribe a chew or topical preventive. Heartworm treatment should be given every month, year round. The heartworm prevention we prescribe the most is Sentinel, which has the added benefit of treating the intestinal parasites roundworms, hookworms, and whipworms. Two of these worms are contagious to people and many other pets.
Compared to treatment, prevention is convenient and inexpensive, and you have the added benefit of knowing that your pet is protected in any event, no matter what they come in contact with.
Give us a call if you have any questions. We’re happy to help you decide what’s best for your pet’s health and well-being.
Conrad Weiser Animal Hospital:
Where big city medicine and surgery meet small town customer service and value.