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An Update on Baylisascariasis: Benign Infection in an Elderly Woman

Body Horrors
By Rebecca Kreston
Apr 13, 2012 8:23 PMNov 19, 2019 11:47 PM


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A timely letter was published in the Emerging Infectious Diseases journal shortly after my article on Baylisascaris procyonis was posted two weeks ago. It describes a quite unusual case of the infection in a recently deceased elderly woman that had lived in British Columbia, Canada. I wanted to write a quick note about this because it changes the dimensions of our understanding of this parasitic infection, challenging the notion of this disease as typically only afflicting infants and toddlers. Additionally, this letter nicely demonstrates how essential autopsies are to the ongoing pursuit of medical knowledge.

The patient was a 73-year-old woman who had suffered from Alzheimer-induced dementia for nearly a decade. She had spent most of her life living in a rural region of British Columbia and, towards the end of her life, as a resident in a nursing home. An autopsy indicated that the cause of her recent death was cardiopulmonary arrest due a large pulmonary embolus or, in layman's terms, a blood clot.

"Baylisascaris procyonis infection in the frontal cerebral lobe white matter. A) Larval nematode seen in multiple transverse sections, surrounded by mild chronic inflammation and reactive changes. B) Morphologic features of the larvae included maximum diameter of 65 ?m; thin, striated cuticle (Cu); single paired lateral alae (Al); and paired excretory columns (EC) that were smaller in diameter than the central intestine (In)." Image & description: Hung T et al. Click for source.

Aside from the expected Alzheimer-associated pathology found in the brain, there was also a number of lesions in the white matter of the left frontal lobe. Each lesion contained a single larva that was identified as B. procyonis, the raccoon roundworm that is rarely found in the human brain. These lesions were surrounded by inflammatory cells and what the authors describe as "mild chronic reactive changes". I take this to mean that there was some fibrosis encapsulating the larva, which is a typical reaction of the body to most parasites and fomites. You can see this in the images published with the letter and reproduced to the left - there are dozens and dozens of little cells with black nucleic surrounding five larva and their density decreases as it radiates outward from the locus of the parasites. A tornado of cells. The brain tissue just looks busy and annoyed, doesn't it?

The authors note that, yes, this woman had dementia which might have masked any of the clinical implications from baylisascariasis. However, there isn't any behavioral or pathological evidence to exclude the fact that this was anything but a benign or mild infection.

Just what am I getting to? This: baylisascariasis might be more common in the population as a benign or sub-clinical infection then us parasitologists had previously thought. I briefly alluded to this in my article by mentioning research of children in Chicago with B. procyonis antibodies but didn't evince any symptoms of infection. There might be a lot more of us walking around with baby raccoon roundworms in our noggins and we might never know until we drop dead of old age and our skulls are cracked open all in the name of science.

There is no definitive way to know just when was this woman was infected. Did she have this infection for decades, having inoculated herself with the eggs around her home in rural British Columbia, or was this a recently acquired infection in the years before her death? Or, did she get the infection as a result of the behavioral manifestations of Alzheimer's disease, as the authors suggest: "More likely, the combination of confusion and poor hygiene and ambulatory state in the patient may have predisposed her to acquiring B. procyonis roundworms through ingestion of contaminated soil." Who knows! It's a parasitological mystery! The best kind, no?

This letter is an exciting and important development for our understanding of this disease on three grounds. First, the case involves the oldest patient on record infected with Baylisascaris procyonis. Second, this marks only the second case from Canada, which may carry epidemiological implications regarding the spread of the parasite and its dynamics with the raccoon population in the country. Data on the parasite’s prevalence in the human population remains super sparse, so the Canadians will just have to keep this case in their back pocket and save it for when new insight into the parasite's prevalence becomes available. Third, and most importantly, this woman seems to have had a totally asymptomatic infection of the parasite. She did not die from the infection and seems to have exhibited no untoward symptoms that one would anticipate considering giant larva babies were lodged in her brain. Her death cannot be attributed to the larva’s presence, just to old age and bad luck.

Autopsies are an incredibly vital and under-appreciated resource in public health and medicine. Without the results of this Canadian's autopsy, we might never know that baylisascariasis can occur in humans as a benign or sub-clinical infection. A few months back, the supremely excellent news agency Pro Publica conducted an investigation into the state of autopsies in America, "Post Mortem: Death Investigation in America". Their articles and research make for a fascinating read and document the decline in forensic facilities, their access to necessary resources to perform autopsies, the numbers of properly trained coroners and forensic pathologists and, critically, an overall decline in the numbers of autopsies performed nationwide. There are a number of reasons why this is the case and I highly recommend a visit to their site where you can brush up on your real-life CSI knowledge. Just be sure to strap yourself in for an alarming few hours of gripping, horror-story reading.

This short research letter has yielded a tiny but important spot of data that tells us more about our immunological response to this fascinating parasite and the scope of its possible disease manifestations. If more autopsies were conducted in the States, we might know a lot more about the parasites and protozoa that hitchhike in our bodies and brains. Information that I know we're all desperately craving for, right?


Hung T, Neafie RC, & Mackenzie IR (2012). Baylisascaris procyonis infection in elderly person, British Columbia, Canada. Emerging infectious diseases, 18 (2), 341-2 PMID: 22305101


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