Heartworm infections, cases per practice on the rise

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Heartworm transmission is expected to increase across the U.S. this year, a result of above-average precipitation and temperatures during 2016, according to the nonprofit Companion Animal Parasite Council.

The prediction follows an increase in heartworm cases over the past several years, according to separate survey results from the American Heartworm Society.

A CAPC announcement from April—which includes predictions about Lyme disease, anaplasmosis, and ehrlichiosis—states that weather conditions have been perfect for breeding by the mosquitoes that transmit heartworms.

“Given the ongoing trend toward above average temperatures and rainfall, CAPC is forecasting high levels of heartworm disease activity in 2017 for most of the country, with an especially active year for the Western United States,” the announcement states.

Forecasted Prevalence of Heartworm 2017
(Courtesy of CAPC)

The AHS survey results show the mean number of heartworm infections seen per veterinary clinic was 22 percent higher in 2016 than in 2013. The data also indicate 23 percent of respondents saw more heartworm cases, and 20 percent experienced a decline.

“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,” AHS President Christopher Rehm said in the announcement. “What caught our attention is that the number of heartworm-positive cases per practice is on the rise.”

AHS incidence maps are available here. The five states with the greatest incidence of heartworm infections in 2016 were, in order, Mississippi, Louisiana, Arkansas, Texas, and Tennessee, the AHS announcement states.

The CAPC predicts more heartworm disease in the lower Mississippi Valley, where it already is rampant, as well as in the Rockies and westward, where heartworm “may not be foremost on the veterinarian’s mind.” Heartworm activity also is expected to be higher than usual in New England, the Ohio River Valley, the Upper Midwest, and the Atlantic Coast states.

But West Texas, from Amarillo to Laredo, is expected to have no increase and may have a decline in heartworm disease cases.

Lyme disease range expanding

The CAPC also predicts Lyme disease will continue expanding its range and warned that veterinarians in the Dakotas, Iowa, Missouri, southern Illinois, Ohio, Kentucky, Tennessee, and North Carolina should be aware of the disease and vigilant in testing and protecting patients. The disease is of particular concern in Pittsburgh and elsewhere in western Pennsylvania, and the council also predicts increased caseloads in New York, northwestern Wisconsin, and northern Minnesota.

Ehrlichiosis problematic, anaplasmosis unchanged

The CAPC is predicting higher-than-usual ehrlichiosis activity in eastern Oklahoma, the Ohio River Valley, southern Virginia, and northern North Carolina. But prevalence could be stable or down in the Great Plains.

The council also predicts no substantial change in anaplasmosis activity in 2017 but recommends testing for it in Northern California, western Pennsylvania, and New York when diagnostics rule out Lyme disease.