One of our employee’s pets, Lightning – a 14 year old Siberian Husky, was brought in several months ago because of a bad tooth. Our plan was to remove the abscessed tooth and clean the remaining teeth under anesthesia which is a straightforward, relatively common procedure. After pre-anesthesia blood testing, Lightning’s story took a strange turn. Her blood tested positive for Heartworm protein, and we confirmed microscopic microfilaria worms were swimming in a drop of her blood. She had never shown any sign of cough, or other respiratory or cardiac illness, but using our ultrasound, we could visualize long, spaghetti – like worms in the pulmonary blood vessels and in her right ventricle of her heart. Lightning was a Tucson dog, raised in a home close to our clinic without extensive time spent out of state – we suspect she acquired her heartworm infection after a mosquito bite here in town.
Lightning is an example of the potential for this disease to affect our pets living in Tucson. She also shows the value of regular heartworm testing and, even more importantly, monthly preventative treatment to stop infection. While she had a successful, (but lengthy) treatment involving injections of medication to slowly kill off the adult worms, prevention is much easier on our pets and their owners.
This condition was discovered over a hundred years ago and was a major issue for working canines in the US Army in the tropics. More recently, heartworm disease has spread world wide including all 50 of the United States. It is highly prevalent in the south and east and around the upper Midwest, but our local incidence appears to be on the rise. Growing up in Tucson, I don’t recall mosquito in our backyard on summer nights, but over the last several years we have been inundated with these biting pests on our back porch. I suspect that pools, evaporative coolers, fountains, landscape irrigation, container plants and rainwater harvesting may all contribute to creating an inviting environment for these insects. In addition, our pet population is as well traveled as we are, many having moved to Arizona from those states in the Midwest, South and East with very high rates of heartworm disease. Many of the dogs that were rescued after Hurricane Katrina were re-homed across the country which increased the spread of the disease. Surveys of the wildlife in our area, particularly coyote populations indicate that a significant percentage carry heartworm and are a potential reservoir for our pets. This map shows the number of reported cases in counties in the Southwest since 2007. Keep in mind, the actual prevalence is much higher as many pets are never tested.
Heartworms are transmitted when a mosquito takes a blood meal from an animal infected with microscopic baby heartworms, and then subsequently bites another animal. Dogs are much more likely to acquire heartworms than cats in the same environments, but our treatment options for cats are much more limited. After the microfilaria (baby heartworms) are introduced, they can mature and migrate to the blood vessels around the heart and cause damage and inflammation to the lungs, heart, and other organs. The take home message is that while heartworm disease in Arizona is less common than in other states, it is emerging as a threat to our pets. The conditions are in place for larger numbers of reservoir or carrier dogs and coyotes which threaten our pets more each year. This condition is much easier to prevent then it is to treat. In the next blog I will talk about Heartworm prevention and treatment.