Every three years, the American Heartworm Society puts out its heartworm incidence map, which reveals much in the way of where heartworm disease is being diagnosed in America. Over 4500 veterinary clinics and shelters submitted data to this project, and at the end of 2016, there were some eye-opening conclusions regarding both the incidence and spread of heartworm disease in dogs nationally.
Let’s start with one broad overall statement: heartworm disease is being diagnosed in all 50 states. There are some clinics that only diagnosed one (or even no) cases a year, but many (mainly along the gulf coast and up the Mississippi River) diagnose over 100 cases a year. The reasons for spread of heartworm disease vary-there are theories that include people migration (with their dogs in tow), and mosquito migration, since mosquitoes are the primary vector.
The top five states in heartworm incidence are Mississippi, Louisiana, Arkansas, Texas and Tennessee-all states that have been in the top 10 since 2001. Nationally, approximately seven of eight surveyed veterinary practices diagnosed heartworm-positive pets during the 2016 calendar year.
While the 2016 AHS heartworm incidence map may not look too much different than the last published map from 2013, there has been an overall increase in the number of heartworm positive cases diagnosed in the U.S.. Within the data, 18 % of clinics noted a decrease in cases of heartworm positive dogs, but the number of heartworm positive diagnosed cases have outpaced that statistic, therefore expanding the reported cases and their respective zones on the incidence map. Veterinarians surveyed noted a 21.7 % increase in the average number of heartworm cases per clinic since the previous survey three years ago.
So how did our clinic fare versus three years ago? We do keep the data, as our veterinary hospital has contributed data on both dog and cat heartworms since 1998. Our data reflected a 12 % increase in heartworm positive as compared to 2013.
So what are my theories that heartworm disease is not just on the rise locally, but nationally overall? Aside from the mobility issue, it comes down to pet owner awareness and pet owner compliance. To put it another way, pet owners must be keenly aware that heartworm disease is real and preventable. However, the product must be given and maintained on a regular dosing schedule.
It’s kind of ironic in that we have more and more good heartworm prevention products on the market every year-pills, liquids, injections and even combination products that kill fleas as well as protect pets from worms and heartworms. Yet, we still are still in pursuit of reducing the case incidences of heartworms in both dogs and cats despite these many tools.
Dr. Chris Duke