Ferret Heartworm Disease
By Dr. Gregory Rich - Avian & Exotic Animal Hospital of Louisiana
Ferret heartworm disease is an insidious and often fatal disease in ferrets. As it is in dogs and cats, heartworm is spread by mosquitoes. All it takes is one bite from a mosquito that has taken a blood meal from a dog or cat that was heartworm positive. Only in parts of Idaho, Montana, and upstate Michigan is this less likely, since heartworm rates among dogs and cats are extremely low in these areas. Although heartworm disease overall is generally low among ferrets, it is still a disease that ferret vets in most of the United States will diagnose on a yearly basis.
Heartworm can affect any ferret over the age of 6 months, whether housed inside or outside. Mosquitos can enter your house through an open door or window, even if you’re careful. After the first bite by a heartworm-infected mosquito, it takes 5 months for the heartworm to mature into an adult worm that will take up residence in the right side of the ferret’s heart. Since this is the same size worm that affects dogs and cats, the overall space it takes up in the ferret’s right ventricle is quite extensive. In addition, we typically find 3-6 worms in infected ferrets, so you can see why ferrets rarely survive this disease.
Symptoms of heartworm can range from very subtle (general malaise) to severe (cardiac and/or respiratory failure). When there are fewer than 2-3 worms present in a young ferret, the ferret will probably “speed bump” a lot and tire easily while playing. Many of these cases mimic an insulinoma case, but when tested, the blood glucose is normal. Severe heartworm infestations often present in severe respiratory distress. In these cases, there are usually 3-6 adult heartworms residing in the right ventricle, preventing the heart from pumping properly, which causes fluid to back up into the lungs and eventually fill the chest cavity. This condition is called pleural effusion. Clinically, these ferrets are usually thin, not moving much, and having extreme difficulty breathing. In x-rays, the whole chest is filled with fluid.
An x-ray showing a ferret’s chest filled with fluid due to a heartworm infestation
Cardiac ultrasound is the most accurate way the assess the presence or absence of heartworms. Not all heartworm tests are accurate for testing ferrets since the worm burden is very low and does not cause a strong enough reaction to turn the most tests positive. In addition, ferrets have the occult (hidden) form of the disease, meaning that baby heartworms are not present in the bloodstream. In dogs, heartworm tests can look for baby heartworms in a blood smear, but this cannot be done with ferrets. However, complete blood counts in ferrets with heartworm disease generally have a marked increase in the Eosinophil count (greater than 10% in my experience).
The primary therapy of choice is injectable Immiticide, a heartworm treatment used in dogs. However, treatment is often risky because the dead worms may move from the heart into the lungs and cause a critical or even fatal pulmonary embolism, which is a blood clot in the lungs. In non-critical cases, Ivermectin (an anti-parasitic) administered every 30 days until the ferret is heartworm-free may be successful. Prednisone (a steroid) may be given orally to diminish swelling caused by dead or dying heartworms moving around the body, especially in the lungs.
Every ferret in areas where mosquitoes live should be on monthly heartworm preventative. The only United States Food and Drug Administration (FDA)-approved heartworm preventative for ferrets and cats is Bayer’s Advantage Multi for cats and ferrets. However, for many years oral Ivermectin was used successfully as heartworm prevention in ferrets. Talk to your vet about the best way to prevent heartworm in your ferrets!
This article originally appeared in Dook Dook Ferret Magazine (Issue 13). To receive 6 new Dook Dook Ferret Magazines per year + get access to other bonuses then join the Ferret-World Membership.