Regional and local temporal trends in the prevalence of canine heartworm infection in the contiguous United States: 2012-2018

Parasites and Vectors

Summary by: Jessica Wenclawiak

Heartworms are common parasites that spread through mosquitoes and infect domestic dogs and coyotes. Since the early 2000’s, veterinarians have diagnosed and reported infections during annual checkups. These tests provide awealth of data on the transmission of the parasite throughout the United States. Previous research has shown that the Southeast experiences the highest number of heartworm infections. To confirm whether this pattern still persists, a team of scientists including CEID member Michael Yabsley analyzed over 57 million heartworm tests from 2012 to 2018 for local and regional trends.

Researchers developed statistical models that used county reports to measure the levels of heartworm prevalence, which is the proportion of positive results among all reported tests in an area. Using this data, the models revealed that the regional patterns of infection mirror previous trends. The southern United States remains the region with the highest number of heartworm cases; Florida had exceptionally low levels of infection, presumably because of its established mosquito abatement programs. Surprisingly, heartworm prevalence has risen along the Mississippi River toward central Illinois and Indiana. On the local scale, infection rates have risen in the central and southern parts of the country, with the exception of the upper Midwest and Michigan. The Pacific coast, on the other hand, showed no significant overall trends.

While the results revealed spatial patterns in heartworm infection, the driving factors behind the parasite’s prevalence remain unclear. Climate, medication resistance, testing practices, and the short-term movement of dogs all influence infection rates on the local or regional levels. Because these factors differ in significance and scale, future research must isolate the strongest predictors of heartworm transmission. When combined with improved reporting and monitoring, this research will help prevent the spread of this common infection.

Self, S.W., et al. (2019). Regional and local temporal trends in the prevalence of canine heartworm infection in the contiguous United States: 2012-2018. Parasites and Vectors,12:380.

Image credit: “Dirofilaria-immitis-microfilaria-dog-blood-film-Giemsa-stain-2” by Alan R Walker, used under CC BY-SA 3.0 / Resized from original