Mosquitoes bring death. Not just the nasty figurative death of a thousand bites. They also bring a slow death of coughing, blood clots, and heart failure. Dogs suffer like my grandfather, after decades of heavy smoking. And heartworm infections are on the rise.
There are several reasons. Mild winters and heavy storms provide ideal mosquito conditions. Missing doses of preventative is the primary reason for dogs (and even cats) to get infected. Shorter winters and heavy spring rains increase the risk of infection before you can start your spring rituals. The American Heartworm Society has been studying the disease for years and has changed its recommendations to better protect your pet.
While it was once believed that seasonal preventative was adequate in northern states, we now know that the preventative should be given year round. This is partially to minimize the risk of starting too late after your pet has been bitten or quitting too early in the fall. Entomologists have confirmed that mosquitoes survive several freezes and become active on a warm winter afternoon. I noticed this phenomenon years ago winter camping in upper Michigan between Christmas and the New Year. Despite a couple inches of snow on the ground at Sleeping Bear Dunes, a mosquito landed on my arm.
People sometime believe that indoor dogs are safe from this scourge. I lost a paper trained indoor only dog, while I worked in Indiana. Apparently his owner, a sweet little old lady who couldn’t get down the front porch without help, had a hole in her screen. She also had poor eyesight. By the time she realized her dog was sick it had suffered serious changes to the heart, blood vessels, and liver. I was able to keep her companion alive for less than a year. Damage to the great blood vessels caused a condition called ‘venous congestion’. Stagnant blood backed up in the liver, starving it of oxygen until dead cells were replaced by a mass of scar tissue.
Changes in recommendations are also due to concerns that the immature heartworm larvae (the only stages affected by preventatives) are getting harder to kill. It is thought that allowing a winter vacation gives the larvae a chance to mature and increase the odds of a partially resistant worm thwarting your efforts to protect your pooch.
Gradual weight gain, especially if your pet is growing or aging, often results in under dosing. Low doses also increase the odds of parasites evolving resistance to common heartworm preventatives. It is feared that may be happening in some southern states already. It is being actively investigated.
But the veterinary profession is fighting back. We have also gained increased wisdom and are learning new tricks to treat the disease. The newer protocols are even safer than they were a couple years ago. We have successfully treated dogs of all ages.
But treatment is expensive. They rely on several medications, including one called Melarsomine. (Immiticide). This drug currently has to be imported from Europe due to a failure in an American manufacturing plant. This has increased the cost. The total treatment process takes several months. It requires activity restriction, so you cannot let your dog romp and play during a critical 2 month period. It is estimated that on average it costs more to treat a dog than to prevent the disease for the dog’s lifetime. That is assuming we catch it early with a yearly blood test and no complications occur during treatment. And even after we cure your dog, you still have to keep it on preventative for the rest of its life. There is no immunity.
We have long known that early detection is critical, allowing treatment before substantial damage has been done to the pulmonary blood vessels. It is now known that larger dogs may hide an infection longer, allowing more damage to occur. This makes the yearly blood tests increasingly important.
Cats are even more complicated (aren’t they always?). The disease is less common in cats, often causing asthma signs. The disease is harder to diagnose and treatment options are limited. Therefore cats that spend significant time outdoors should be on Revolution for heartworm prevention, as well as flea and ear mite control.
Dogs should be on preventative year round and weighed regularly. Depending on your dog’s lifestyle we may recommend Heartgard plus, Revolution, or Trifexis. Dogs should be blood tested every year. Dogs that are allowed to become infected need to be treated using the newest drug protocols.
Alex Cole, DVM