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Posted May 29, 2014 in Dog Diseases & Conditions A-Z

Most people are unaware that the cute little bandit that raids your trash and digs up grubs from your perfect lawn is likely also harboring a dangerous parasite. The parasite is called Baylisascaris (bā′lis•as′kä•ris), and the animal that carries it is the wily raccoon. Most animal species have their own set of parasites. Raccoon parasites are particularly concerning, in no small part because of Baylisascaris.

What is Baylisascaris?
It’s important to recognize that raccoons (like all wildlife) usually carry diseases, some of which are relevant concerns for both people and pets. One such concern to be aware of is Baylisascaris procyonis, also known as the raccoon roundworm. Baylisascaris procyonis is a common, large roundworm parasite that resides in the small intestine of the raccoon. This parasite can infect a variety of mammals including dogs and on occasion humans.

How is Baylisascaris transmitted?
Like so many intestinal parasites, infection occurs when the eggs of the worm are inadvertently ingested or when small, infected animals are eaten by raccoons. Infected raccoons can shed millions of eggs daily in their feces. These eggs become infective under proper conditions in about 10-14 days.

Where does this parasite occur?
Baylisascaris occurs wherever raccoons live. Infected raccoons have been found throughout the United States, though mainly in the Midwest, Northeast, Middle Atlantic, and West Coast.

How common is Baylisascaris in raccoons?“Raccoon"
Prevalence of infections range to nearly 100% of all raccoons sampled depending on region and time of year, according to the Michigan Department of Natural Resources.

Can Baylisascaris spread to dogs?
Yes, Baylisascaris can spread to dogs, which can also increase the likelihood of human exposure. We don’t know how prevalent it is in dogs but because we do know it can be dangerous, we should always be on the lookout. Baylisascaris eggs look similar to dog roundworms so careful and critical identification is important.

What are the signs of Baylisascaris in dogs?
As with other roundworms, the mature worm lives in the intestines while the immature form migrates through the body of the puppy (see roundworm infections). There are two forms the disease can take in dogs:

  • Intestinal, which is the typical adult form and like other intestinal parasites results in intestinal signs like diarrhea.
  • Visceral, which is more common in puppies and is known to cause neurologic diseases that can mimic canine distemper, encephalitis and even rabies.

Can humans be infected by Baylisascaris?

Related symptoms: 

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Mike has more than 35 years of experience in companion animal veterinary practice and is a valued member of IDEXX’s Pet Health Network team since 2013.