Heartworm Disease in Cats
What is Heartworm Disease?
Heartworm disease is a potentially fatal illness that poses a significant threat to pets worldwide. Caused by foot-long worms that live in infected animals' heart, lungs, and blood vessels, heartworm infection can lead to severe lung disease, heart failure, and damage to other organs. While dogs are the most common hosts for heartworms, these parasites can also infect other mammal species, including wolves, coyotes, foxes, sea lions, and even in rare cases, humans.
Dogs are the natural host for heartworms, which means the worms can mature into adults, mate, and produce offspring within their bodies. If left untreated, dogs can harbor several hundred worms, causing lasting damage to their heart, lungs, and arteries that can impact their health and quality of life long after the parasites are dead. Therefore, preventive measures are crucial, and treatment should be administered as early as possible if needed.
Heartworms exposed in internal organs of a dog during necropsy.
While heartworm disease in dogs is well-known, many pet owners are not aware of its impact on cats. Unlike dogs, cats are atypical hosts for heartworms, and most worms do not survive to the adult stage. While cats with adult heartworms typically have only 1 to 3 worms, even immature worms can cause significant harm in the form of heartworm-associated respiratory disease (HARD). Additionally, the medication used to treat heartworms in dogs is not effective for cats, making prevention the only way to protect felines from this disease's effects.
How is Heartworm transmitted?
The mosquito plays a crucial role in the life cycle of heartworms. In an infected dog, fox, coyote, or wolf, adult female heartworms produce tiny baby worms called microfilaria that move around in the bloodstream. When a mosquito bites and feeds on an infected animal, it picks up these baby worms. Over the next 10 to 14 days, the worms develop and mature into infective larvae. When the mosquito bites another susceptible animal, the infective larvae are deposited onto the skin and enter the new host through the mosquito's bite wound. It takes around 6 months for the larvae to mature into adult heartworms inside the new host. Adult heartworms can survive for 5 to 7 years in dogs and up to 2 or 3 years in cats. Since heartworms have a long lifespan, every mosquito season can result in an increased number of worms in an infected pet.
What are the symptoms of Heartworm infection in cats?
Cat heartworm disease can present itself in very subtle ways, while others can be quite severe. Common symptoms include coughing, vomiting, a lack of appetite, and weight loss. In some cases, a cat may experience difficulty walking, fainting or seizures, or fluid buildup in the abdomen. A cat may collapse or even die suddenly in more severe cases, with little to no warning.
How significant is the risk of Heartworm to my cat?
Heartworm disease is a growing concern and can affect pets even in areas where it seems unlikely. Factors such as the relocation of infected animals and the presence of wildlife carriers contribute to the spread of heartworm disease. Heartworm disease has been reported in all 50 states, and the risk factors are unpredictable. The American Heartworm Society recommends testing pets for heartworms every 12 months and giving them preventive all 12 months a year. This approach is known as "Think 12."
What about testing?
Heartworm testing is important as early detection increases the chances of recovery. A veterinarian can perform the test with just a small blood sample to detect the presence of heartworm proteins. Cats are less likely to have adult heartworms, making it harder to detect infection, so screening may include the use of an antigen and antibody test, as well as x-rays or ultrasound. Prevention is critical as cats have no approved treatment for heartworm infection.
What if my cat tests positive for Heartworm?
Cats can get heartworms, but the disease presents differently than in dogs, and treatment options are limited. Even one or two worms can cause severe illness and may lead to permanent respiratory damage. Because cats are not ideal hosts for heartworms, some infections can resolve on their own, but they can cause respiratory system damage. Heartworms in the circulatory system also affect the cat’s immune system, causing symptoms like coughing, wheezing, and difficulty breathing. Heartworms can even migrate to other parts of the cat’s body, such as the brain, eyes, and spinal cord. Blood clots in the lungs and lung inflammation can also result when the adult worms die in the cat’s body.
If your cat tests positive:
Wizard, a cat at Richmond Animal League, tested positive for heartworms at the transferring shelter. He recieved steroid treatment to stabilize and was adopted to a loving home.
Diagnosis involves various tests and management. Monitoring and monthly prevention are crucial.
Treatment only focuses on stabilizing the cat and determining a long-term management plan. Unfortunately, there is no approved drug therapy for cats, and the drug used for dogs is not safe for use in cats. Monitor your cat for any symptoms of respiratory issues. Your veterinarian may recommend hospitalization to provide supportive care.
Preventives are available in pill or spot-on form and should be given monthly to all cats to prevent new infections. Indoor cats are also at risk and should be given prevention as there is no 100% effective way to prevent mosquitos from getting inside your home.
While heartworm infection in cats is rarer than in dogs, it is still a threat to our feline friends. Monthly prevention is the only way to protect your cat from heartworms and many monthly flea preventions contain heartworm prevention as well.
References:
Heartworm in Cats. (2001, January 24). American Heartworm Society. https://www.heartwormsociety.org/heartworms-in-cats
Clyde-Druin, E. (2022, April 8). Feline Heartworm Disease: Separating Fact from Fiction. Today’s Veterinary Practice. https://todaysveterinarypractice.com/parasitology/feline-heartworm-disease-separating-fact-from-fiction/
