A couple of days ago, I mentioned that Jason Stull and I have done a scoping review of human Baylisascaris procyonis (raccoon roundworm) infections. The paper is published in the Canadian Veterinary Journal, but won’t be open access until October, so I’ll provide a preview of some of the findings here. Here’s a snapshot of what we covered:

• 60 infections in people were described.
• 47 had neurological disease, 9 also had ocular disease, 11 just had ocular disease, and there was one case each of eosinophilic cardiac pseudotomour and an incidental finding during an autopsy.
• Most cases were from the US (52), followed by Canada (5), Germany (2) and Brazil (1)
• 75% of cases were male, with a median age of 2.9 years (range 9 months to 73 years)
• 12 (25%) of people had been observed to eat feces, dirt or other potentially contaminated material; 75% of these cases were less than 5 years of age.
• 5 patients had developmental delay and 1 had Down’s syndrome.
• Of the people with neurological disease for which an outcome was reported, 19% died, 10% fully recovered and 71% had mild to severe residual neurological deficits.
• 70% of patients with ocular disease had permanent vision loss.

Hopefully that sets the scene a bit. Today, I’ll focus on sources of infection / exposure. I very often get questions from people asking if “X” creates a risk for B. procyonis exposure. Most often, it’s really unlikely but I usually can’t say “never.” That’s not always well received, since people are typically looking for re-assurance, so the messaging can be tough. “Non-zero but as close to zero as you can get” is my somewhat convoluted but honest answer in a lot of situations.

But, what do the data say to support that answer? Not a lot, unfortunately. Data support what we think of as high risk exposures, but also show that there’s some degree of risk from more casual situations.

The data from our review were limited, since source of infection was only investigated for a subset of cases, and retrospective investigation of sources can be tough – particularly when a large subset of affected people are young children or others who can’t provide a reliable history. Our relatively small number of reported cases (60) dwindled to 37 with an attributed source, and many of those sources weren’t proven, but just logical assumptions.

Prior to this review, I would have said that young kids or people with developmental delay that are prone to eating inappropriate items outside were the highest risk groups, and that casual contacts with the environment (and even raccoons) were low risk. That still largely holds true. The presumed sources in these cases were:

• pica (inappropriate ingestion) in an area where raccoons were observed (n=10)
• having abundant raccoon activity in the area (n=8)
• hiking or working in areas with many raccoons (n=4)
• having raccoon latrines on the property (n=4)
• having a pet raccoon in the house (n=4)
• a history of pica but unknown raccoon exposure (n=2)
• storing raccoon pelts where a child played (n=1)
• raccoon infestation of a fireplace (n=1)
• ingestion of food scraps from public garbage cans (n=1)
• seeing raccoons in the neighbourhood (n=1)
• possible source not reported (n=23)

If we look at the two most recent reported cases that were not in our scoping review, one was a child with pica whose home had a raccoon latrine on a roof that allowed feces to drop to the ground below. The other was a young child that was known to (as per normal for young kids) put soil and bark mulch into their mouth. There were no known raccoon latrines in the area, but raccoons were active locally. This largely fits with my assumptions that risk is highest in a definable population that is prone to ingesting things they shouldn’t outside, amplified by the presence of a local raccoons and raccoon latrines.

Some cases had no clear route for ingestion of parasite eggs, but there was a high level of environmental contamination locally, particularly in the form of a local raccoon latrine. That makes sense too since the egg burden can be really high around latrines. If people touch the ground in those areas then inadvertently touch their mouths (a very common event), infection would be possible.

Having a pet raccoon… that’s obviously a problem. It’s one of the reasons we emphasize that raccoons should not be pets (aside from it being illegal in Ontario). Wildlife should be left in the wild or transferred to a proper rehabilitation facility. (Though a recent experience of one of my daughter’s friends finding a baby raccoon and not being able to find a rehabilitator to take it for weeks shows some challenges with that too.)

The people who got infected with no clear source beyond knowing there were raccoons in the area are the most challenging part of the puzzle. Millions upon millions of people live in areas where there’s abundant raccoon activity. These data show there may be some risk from being in those environments. At the same time, while published reports are only a subset of true cases, the number of infections in people is still really low. When you have a situation where millions of people are exposed and a handful get sick, it’s tough to find the right message. The risk isn’t zero, but it’s really, really low.

What this tells me is that the general public shouldn’t fear Baylisascaris and freak out if they see a raccoon walking across their yard. They should take it as a reminder that there are lots of diseases out there in nature, and that we should use common sense (e.g. stay away from raccoons, don’t eat poop) and hygiene (wash your hands) to minimize our risk of exposure.

Who’s not on the list of cases in this report? Raccoon rehabilitators.

The case linked to a pet raccoon shows that keeping a raccoon can create risk, which isn’t surprising. However, there are lots of wildlife rehabilitators that have abundant contact with raccoons and raccoon feces. Previous study has reported antibodies against the parasite in 5-7% of raccoon rehabilitators, showing they can be exposed, but the risk of disease is clearly limited. That’s an important thing to keep in perspective – simply encountering the parasite isn’t enough to cause infection. There’s likely a dose component (more eggs ingested mean more larvae that migrate and cause tissue damage) and a chance component (migration is random, and if the larvae don’t happen to end up in the brain or eye, there may be no issues).

What can the average person do to avoid Baylisascaris?

It comes down to don’t eat raccoon poop:

• Supervise kids and people with developmental delay when outside, especially young kids and anyone prone to inappropriate ingestion.
• Avoid putting high risk people in areas where contamination with raccoon feces is likely (e.g. near a latrine, or where feces have been observed).
• Stay away from raccoons.
• Discourage raccoons from living around people’s properties and public places like parks (e.g. don’t feed them).
• Identify and properly clean up raccoon latrines.
• Don’t keep raccoons as pets.
• Use good hygiene practices if there is any contact with raccoons (e.g. rehabilitators).
• Use good hygiene practices, especially hand hygiene, after contact with soil (which is a good general practice that protects against other diseases too, like toxoplasmosis)

These data support the need for hedging, unfortunately. That means we usually can’t say a scenario has zero risk. However, near-zero risk is common, and we have to keep things in perspective. I’m still going to have to answer most with “the risk is really, really low and I wouldn’t worry about it” vs “there’s no risk.”