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Heartworm cases on the rise

Heartworm cases on the rise
Dog owners have to do more to keep their dogs protected against heartworms. The parasitic worms calledDirofilaria immitis are spread through the bite of a mosquito that carries them in a larval state.

It is an especially grisly disease. Once a dog is infected with the larva, it can grow into a foot-long parasitic worm that invades the dog's cardiovascular system, damages the arteries that carry blood from the heart to the lungs and blocks blood flow to the lungs by their presence and the clots they can cause.

To spread from one dog to another, the larvae have to develop to a specific infective stage inside the mosquito. The hotter it gets, the more quickly the larvae mature into a form that can transfer from the mosquitoes to the dogs. When it's 71 degrees out, that process can take 16 to 20 days. If it's 82 degrees, it takes 11 to 12 days, said Bruce Kornreich, a cardiologist and professor of veterinary medicine at the Cornell University College of Veterinary Medicine in New York. 

Heartworm disease has historically been a problem in the South and Southeast. Environments farther north are now able to support the mosquitoes that transmit it and the larvae that cause it. 

Infections are rising. From 2013 to 2016, there was a 21.7% increase in heartworm infections in the number of dogs per veterinary clinic testing positive for heartworm, said Christopher Rehm, a veterinarian who practices in Mobile, Alabama, and is president of the American Heartworm Society.

There are no solid figures on how many dogs heartworm disease kills each year, but untreated infections shorten a dog's lifespan. 

"Based on my own anecdotal experience, I would conservatively estimate that heartworm-infected dogs lose one-third of their lifespan if not treated properly and in a timely manner," Rehm said. 

As the parasite moves into new areas, owners may not always be aware they need to be on the lookout for it. It's also a problem for more months of the year, Foley said.

"A hot winter means the mosquitoes don't die back, so they're raring to go as early as January and start spreading heartworm," she said.

Pet owners across a wider swath of the USA need to give their dogs preventive medicine to keep them from getting heartworms. People in areas where heartworm infections were a problem only in the summer now must treat their dogs for more months out of the year. 

Since 2010, the American Heartworm Society and the federal Food and Drug Administration have recommended year-round preventive treatment, because the disease is more prevalent and it's so devastating to dogs who get it, Kornreich said. 

Even if heartworm disease is caught and treated in time, it takes its toll on dogs. "Once they've ever had a heart infection, they're never the same," Rehm said. 

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