Backyard raccoonThe August edition of Emerging Infectious Diseases has an interesting case report of Baylisascaris procyonis infection in a California man (Langelier et al. 2016). Baylisascaris procyonis, commonly known as the raccoon roundworm, is a parasite that is very commonly found in the intestinal tracts of raccoons. Massive numbers of parasite eggs can be found in areas where raccoons congregate to defecate (raccoon latrines). When a person ingests these eggs and they hatch, the parasite larvae can migrate throughout the body, particularly the brain, and cause significant damage.

This report details infection of a previously healthy 63-year-old man. His course of disease included 2 weeks of progressive fatigue and neurological abnormalities (e.g. confusion, headache, trouble moving his arm and head). He was hospitalized and continued to deteriorate. A sample of CSF (the fluid that surrounds the spinal cord and brain) had a few abnormalities, including an increase in eosinophils, a cell type that is often found in allergic and parasitic diseases. This led the physicians to consider an additional range of possible causes, and to ask some important questions. This questioning led them to discover that, among other things, the patient had recently undertaken a project under his house, where raccoons had been observed. As a result, they considered the potential for B. procyonis and started treatment while awaiting test results. Results were ultimately positive for the parasite.

A few noteworthy points:

  • It’s impressive that they considered B. procyonis. It took until eosinophilia was identified in the CSF to ask the critical questions about exposure, but at least they were asked fairly early in the process. This is a rare infection that wouldn’t normally jump to mind. A good history that included potential direct and indirect animal contact was the key. If they hadn’t gotten information about potential exposure to raccoon feces, they probably wouldn’t have tested. A good history goes a long way, but history-taking sometimes seems like a lost art.
  • Disease from this parasite in an otherwise healthy adult is very rare. Most of the small number of infections of which I am aware have been in young kids or kids with behavioural issues that made them higher risk for ingesting strange things like raccoon feces. Inadvertent exposure of a relatively healthy adult is unusual.
  • The patient responded reasonably well to treatment, particularly when compared to the usual (devastating) outcome. Whether this was because he was an adult, the infective dose was low, treatment was started early or he was lucky is unknown. It’s encouraging though, and another reason that getting a good history early in disease is so important. Early diagnosis (or even early consideration of infection) can lead to early treatment and better outcome.