The raccoon ascarid. A probable cause of human ocular larva migrans.

The ability of raccoon roundworm larvae, Baylisascaris procyonis, to produce ocular larva migrans (OLM) was studied in various experimental animals. In addition, the clinical and pathologic lesions were compared to those in suspected cases of human ocular baylisascariasis, in patients with diffuse unilateral subacute neuroretinitis (DUSN). Ocular larva migrans was produced in squirrel monkeys, cynomolgus monkeys, mice, hamsters, grey squirrels, and woodchucks orally infected with B. procyonis eggs. The clinical and histologic lesions were primarily those of retinitis, retinal hemorrhages, retinal tracks, disruption, and vasculitis; pigment migration; choroiditis; vitritis; and free or encysted larvae in ocular and extraocular tissues. The lesions of experimental OLM correlated well with those of suspected cases of human ocular baylisascariasis and DUSN. Based on these studies, B. procyonis of raccoons should be considered as a probable cause of OLM and DUSN in humans.