A loyal reader sent in this wonderful photomicrograph from a recent case of cerebral Baylisascariasis (click on the picture to see it up close). A cause of eosinophilic meningoencephalitis, infection with Baylisascaris procyonis is typically characterized by necrosis and eosinophilic inflammation. Larvae are often encapsulated within fibrous tissue ( reference 1 ). Although not particularly neurotropic, the larvae may reach the central nervous system and cause major tissue damage.
Baylisascaris procyonis is an intestinal roundworm endemic to the US raccoon population. Humans are infected by ingestion of worm eggs in raccoon feces. The median age for human infection is just over one year old, consistent with the propensity of young children to explore their environment orally (surprising that this behavior has not been naturally selected out of humans over the millenia!). I came across only one report of clinical recovery after infection ( reference 2 ). Otherwise, cerebral Baylisascariasis results in either severe neurologic damage or death. That being said, subclinical infection has been suggested by a study in Chicago, which found 30 (8%) of 389 children 1–4 years of age were seropositive for B. procyonis, although none had experienced symptoms ( reference 3 ).
The most common cause of eosinophilic meningitis in the United States is the presence of a ventriculoperitoneal shunt; but worldwide it is infection by Angiostrongylus cantonensis. In addition to Bayliscaris procyonis, other infectious causes of eosinophilic meningitis include Toxocara spp., Gnathostoma spinigerum, and neurocysticercosis (source: reference 2 ).
References: 1. Love S, et al, eds. Greenfield's Neuropathology, 8th edition. p. 1479. 2. Pai et al. Full recovery from Baylisascaris procyonis eosinophilic meningitis. Emerging Infectious Disease 13(6) p 928-30. June 2007 3. Brinkman WB, Kazacos KR, Gavin PJ, Binns HJ, Robichaud JD, O'Gorman M, et al. Seroprevalence of Baylisascaris procyonis (raccoon roundworm) in Chicago area children. In: Program and abstracts of the 2003 Annual Meeting of the Pediatric Academic Societies, Seattle, Washington; 2003 May 3–6. Abstract 1872. [cited 2007 Mar 29]. Available from http://www.abstracts2view.com/pasall/authorindex.php