Most people would think Pip didn’t need to be on heartworm prevention because he is indoors only – but mosquitos frequently get into any household and can find their way to a warm-bodied animal with relative ease. Most people would also think that Pip would be protected by his long hair – but haven’t you gotten a mosquito bite through clothing or on your scalp? Pip’s youth would also lead most people to think it would be impossible for him to have heartworms, but it only takes 4-5 months for a heartworm to reach adulthood in a cat and the summer months are the most common time of transmission, coinciding perfectly with Pip’s history.
Pip’s intermittent symptoms also follow the typical course of heartworm disease, showing up at first when the larvae migrate into the lungs, then only intermittently until the heartworm dies.
Pip’s case also presents how difficult it is to diagnose heartworm disease in cats. Pip showed no radiographic evidence of heartworm disease, his blood tests were negative, and it was only on ultrasound that heartworm infection was identified! Pip has only 1 or 2 heartworms, a very common occurrence in cats, and both heartworms are likely to be male, resulting in a negative antigen test. His heartworm antibody test is either false negative or his body is not actively producing a high number of antibodies against the heartworms, anther common occurrence in cats. X-rays are relatively insensitive in identifying heartworm disease in cats but can be very good indicators of the extent of infection and damage to the body if signs are present on x-rays.
So what happens to Pip now that we have diagnosed a heartworm infection? Because cats can’t receive the same heartworm treatment as dogs do, it is very difficult to treat cats for heartworm disease. Immiticide, the treatment we use in dogs, is not at all tolerated in cats and can’t be used. The only other option to definitely treat heartworms in cats is to surgically remove them, a procedure which is very risky and expensive. Often, we treat cats with heartworm disease symptomatically and supportively while the heartworm ages and dies. If a cat is symptomatic for infection (is showing signs like respiratory distress, vomiting, lethargy, or any other sign), those symptoms are treated. Most cats with heartworm disease are also started on steroids to decrease the inflammation associated with the infection and hopefully decrease the likelihood of an allergic reaction should the heartworm die and begin to break apart. A monthly heartworm preventative is given every month to weaken the adult worms and to prevent infection with more heartworms. A third medication is used to help shorten the lifespan of the heartworm by killing a bacteria called Wolbachia which helps support the heartworm; this medication is an antibiotic called doxycycline. Treatment is always determined on a case-by-case basis and depends on many factors which our veterinarians take into account to decide which treatments best fit each cat and their owners.
What is the best way to save your cat from heartworms? Use a monthly heartworm preventative every month, year-round. Many heartworm preventatives also prevent intestinal parasites which may be contagious to people, protecting you and your pet at the same time. Certain heartworm preventatives also prevent fleas and earmites!
While heartworm disease is slightly less common in cats and the worm-burden is often lower, heartworm disease in cats is much more difficult to diagnose, treat, and survive. Please think of Pip the next time you hear someone say their indoor cat doesn’t need to be on heartworm prevention.
Pip is an actual patient and his owner has been kind enough to allow us to share his story in hopes that he can save other cats from a similarly uncertain fate. Pip is alive and well as he undergoes treatment for heartworms by supportive care.
If you have any questions, please feel free to call us anytime. You can also visit the American Heartworm Society’s website for more information