By Dean L. Winslow, MD, FACP, FIDSA

Professor of Medicine, Division of General Medical Disciplines, Division of Infectious Diseases and Geographic Medicine, Stanford University School of Medicine

Dr. Winslow reports no financial relationships relevant to this field of study.

SYNOPSIS: During a two-year period, six cases of neural Baylisascaris larva migrans and one case of ocular larva migrans were identified by case report forms and serologic testing submitted to the Centers for Disease Control and Prevention. All patients survived, but some were left with severe neurologic sequelae.

SOURCE: Sircar AD, Abanyie F, Blumberg D, et al. Raccoon roundworm infection associated with central nervous system disease and ocular disease — six states, 2013-2015. MMWR Morbid Mortal Wkly Rep 2016;65:930-933.

From May 2013 to December 2015, Baylisascaris serologic testing results from serum, cerebrospinal fluid (CSF) samples, or both submitted to the Centers for Disease Control and Prevention (CDC) along with case report forms were reviewed. Serologic testing done at CDC relied on a recombinant antigen rBpRAG1 immunoblot assay. Six cases of neural larva migrans and one case of ocular larva migrans were identified. All of these cases had positive results by rBpRAG1 and had negative serologic tests for Toxocara spp.

All seven of the cases had either documented or likely exposure to raccoons or raccoon excrement. Four patients were children (10 months, 15 months, 3 years, and 7 years of age). One patient was a 31-year-old with developmental delay who owned a pet raccoon. A 63-year-old contractor was reported retrospectively by his family to generally eat without washing his hands. A 32-year-old woman had no direct exposure but often hiked in rural areas frequented by raccoons.

All of the patients with neural larva migrans presented with eosinophilic meningitis with variable signs of encephalitis. One patient who underwent MRI had large enhancing brain lesions seen on imaging, which completely resolved with corticosteroid treatment without antihelminthic therapy. Most of the patients were treated with albendazole plus corticosteroids. All patients survived. Four patients had residual neurologic deficits, and two patients recovered fully.

The patient with ocular larva migrans was a 7-year-old boy from rural Minnesota who presented with worsening vision of his right eye. Ocular examination revealed a larva consistent with Baylisascaris procyonis. He was treated with albendazole, corticosteroids, and retinal photocoagulation laser therapy, and his vision recovered nearly completely.


B. procyonis is a roundworm found throughout North America, and is especially common in the Northeast, Midwest, and West Coast of the United States. Infected raccoons are generally asymptomatic. B. procyonis eggs are passed in raccoon feces, and the eggs become infectious after some weeks to months in the environment. Humans become infected when they ingest eggs (generally contaminating soil where raccoons have defecated). Then migration of the larval form in humans can result in fatal neurologic disease if not diagnosed and treated promptly. It is likely an under-diagnosed and under-reported disease. Children are disproportionately infected due to their tendency to place fecally contaminated objects or fingers in their mouths. Preventive measures would include such things as safely clearing “raccoon latrines,” washing hands after contact with soil, and vigilance with small children. The CDC report suggested “pre-emptive treatment” with albendazole following suspected exposure to raccoon feces. This did not seen very feasible to me; however, prompt empiric treatment with albendazole (plus corticosteroids) might be life-saving in the right clinical and epidemiological setting since serologic testing results might take many days to be available.