Heartworm in Dogs, Part 2: Prevalence

In last week’s The Vet Is InDr. Palazzolo provided an overview of canine heartworm. This article will address how prevalent it has become nationwide and in the Los Angeles area.

Graphic courtesy of County of Los Angeles Public Health Department.

More than one million pets in the United States have heartworm disease, an infection caused by a mosquito-borne worm called Dirofilaria immitis. It is prevalent in all 50 states and around the world. Since it involves mosquitoes, those parts of our country with humid and wet conditions have the most problems. This tends to occur in the eastern half of our country, especially the southeastern section.

Urban sprawl in the northern United States has increased the temperature in certain areas. This extends the heartworm season to what used to be the colder months, leading to more mosquitoes.

Stray dogs and wildlife can be carriers, so there is always a reservoir of this disease in nature. Mosquitoes can be blown great distances by the wind, spreading this problem to the drier areas of our country. Mosquitoes can easily infect indoor dogs.

Many people travel throughout the country with their dogs and can be exposed to heartworm-infected mosquitoes. Heartworm-infected dogs that were adopted after Hurricane Katrina were sent throughout the country, helping to spread this disease. Dogs that are illegally imported can also harbor heartworms and help spread the disease to our local dogs.

Graphic courtesy of County of Los Angeles Public Health Department.

From 2007 to 2016, there were 303 cases of heartworms in dogs in Los Angeles County. Of these, 77 percent had no symptoms when diagnosed. In 21 percent of these cases, the dog had not been treated, increasing the amount of Dirofilaria immitis-infected mosquitoes in the environment.

There is a new species of drought-resistant mosquito in Los Angeles County, called Aedes. They have transmitted heartworms in other countries, and are being monitored here. Please consult your vet if you believe that your dog may have come in contact with infected mosquitoes.

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Kate Karp is the Pets Columnist for the Long Beach Post covering the world of animal activism, pet adoptions and lots of cute cats. She’s called Long Beach home since 1994 and has written for the Post for about 10 years. Kate’s day job is as a copyeditor, which she discovered a love for during her 30-year tenure as a teacher. She describes the job as “like taking the rough edges off a beautiful sculpture.”
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