This article examines the individual factors that influence prevalence rates of canine heartworm in the contiguous United States. The data set pictured below was provided by the Companion Animal Parasite Council, which contains county-by-county results of over nine million heartworm tests conducted during 2011 and 2012, is analyzed for predictive structure. The goal is to identify the factors that are important in predicting high canine heartworm prevalence rates. Please note that Reno, Sparks, Lake Tahoe and Truckee areas are shaded Red and/or Orange indicating that our pets are at high risk of contracting heartworm disease.

The factors considered in the study by the Companion Animal Parasite Council where those envisioned to impact whether a dog is likely to have heartworm. The factors they examined included climate conditions (annual temperature, precipitation, and relative humidity), socio-economic conditions (population density, household income), local topography (surface water and forestation coverage, elevation), and vector presence (several mosquito species). A baseline heartworm prevalence map was constructed using estimated proportions of positive tests in each county of the United States. A smoothing algorithm was employed to remove localized small-scale variation and highlight large-scale structures of the prevalence rates. Logistic regression was used to identify significant factors for predicting heartworm prevalence.

All of the examined factors have power in predicting heartworm prevalence, including median household income, annual temperature, county elevation, and presence of the mosquitoes Aedes trivittatus, Aedes sierrensis and Culex quinquefasciatus. Interactions among factors also exist.

The factors identified are significant in predicting heartworm prevalence. The factor list is likely incomplete due to data deficiencies. For example, coyotes and feral dogs are known reservoirs of heartworm infection. Unfortunately, no complete data of their populations were available and 2011-2012 is the latest set of data that we have available. The regression model utilized by the Companion Animal Parasite Council is currently being explored to forecast future values of heartworm prevalence.

Remember: We live in a High-Risk area and Heartworm is a serious and often fatal disease. And…IT IS TOTALLY PREVENTABLE.

Dr. Sarah Kalivoda
Mountain View Animal Hospital & Holistic Pet Care
Reno, Nevada