Heartworm Incidence Moves Upward

By Vet-Advantage
August, 2017
Survey of U.S. veterinarians uncovers per-practice increase in heartworm-positive cases

While the hotbeds of heartworm disease haven’t changed dramatically in the past three years, the incidence numbers reported by participants in the 2016 American Heartworm Society (AHS) Incidence Survey indicate that the average number of positive cases per veterinary clinic has been moving upward. In addition to announcing its latest survey data, the AHS unveiled a new heartworm incidence map based on data from veterinary practices and shelters across the country.

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The average number of dogs diagnosed per clinic in 2016 rose by 21.7 percent over 2013 numbers, according to AHS President Christopher Rehm. “When veterinarians study our new heartworm incidence map, they will note that the distribution of heartworm cases hasn’t changed dramatically since we surveyed veterinary practices three years ago. What caught our attention is that the number of heartworm-positive cases per practice is on the rise.”

Of respondents participating in the AHS survey, 23.3 percent reported seeing more heartworm cases in 2016 versus 2013, while 19.8 percent reported a decline in their practice areas.

Heartworm infection diagnosed nationwide
No state in the U.S. is heartworm-free, according to the AHS survey, which revealed the top five states for heartworm incidence were Mississippi, Louisiana, Arkansas, Texas and Tennessee – all states that have been in the top tier since the AHS began tracking incidence data in 2001. Rounding out the top 10 states were South Carolina, Georgia, North Carolina, Alabama and Florida. Among the top 10, only Alabama, Louisiana and Texas saw decreases in the per-practice averages of dogs diagnosed, while increases were noted in the other seven.


Compliance is key to reducing heartworm incidence
On a more hopeful note, survey results indicate that reducing heartworm incidence is in the hands of veterinarians and pet owners. Among veterinarians who reported a drop in heartworm incidence since the 2013 survey, 64 percent attributed the change to owner behavior, including increased usage of heartworm preventives and improved owner compliance. Veterinarians who reported incidence increases agreed: Almost half (47.8 percent) cited failure to give preventives, skipping doses or failing to give preventives year-round as contributing factors.

Other factors believed to contribute to incidence increases in certain regions were weather conditions conducive to heartworm transmission in 2016 and the movement of infected dogs into practice areas. Insufficient efficacy of heartworm preventives was only considered a factor by 3.3 percent of those veterinarians who saw incidence rise.

“We see the results of the AHS Incidence Survey as a good news/bad news story,” says Rehm. On one hand, heartworm incidence has increased in a number of states, especially those states in the most heartworm-endemic areas of the Southeast, Mid-South and Delta regions, he says. On the other hand, he adds, veterinarians indicate that there is a straightforward answer to this: First, convince more pet owners to use preventives, and second, convince them to protect their pets year-round – with no lapses.  

Topics: Trends, Heartworm

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