Visceral and neural larva migrans in rhesus macaques

Abstract

Large ascarid larvae within granulomas were noted histologically in the mesenteric and pancreatic lymph nodes of 13 of 21 rhesus macaques (Macaca mulatta) euthanized as part of an experimental viral pathogenesis study. In addition, 7 of the 13 monkeys had cerebral granulomas, which in 4 animals contained nematode larvae similar to those within the lymph nodes. Despite the lesions, the animals did not show clinical signs associated with the parasitic infections. Characteristics of the larvae included, on cross-section, a midbody diameter of approximately 60 to 80 mum, a centrally located and slightly compressed intestine flanked on either side by large triangular excretory columns, and prominent single lateral cuticular alae. The morphology of the larvae was compatible with Baylisascaris spp. Baylisascariasis is a well-described infection of animals and humans that is caused by migrating larvae of the raccoon roundworm, Baylisascaris procyonis. A similar species, B. columnaris, is found in skunks and can cause cerebrospinal nematodiasis, but most reported cases of baylisascariasis have been due to B. procyonis. Our macaques were born free-ranging on an island in the southeastern United States where raccoons, but not skunks, were found to be common inhabitants, indicating that B. procyonis was the most likely parasite involved. These cases are similar to the low-level or covert cases of Baylisascaris infection described to occur in humans and provide further evidence of the existence of this parasite in the southeastern United States.

Figure 1.

Rhesus macaque mesenteric lymph node section showing cross-sections of a Baylisascaris spp. larva within an eosinophilic granuloma. Hematoxylin and eosin stain. Magnification, ×200.

Figure 2.

Rhesus macaque brain section showing an eosinophilic granuloma containing cross-sections of a Baylisascaris spp. larva similar to those within the lymph nodes. Hematoxylin and eosin stain. Magnification, ×400.

Figure 3.

Brain section showing at higher magnification a Baylisascaris spp. larva. Larval characteristics on cross-section were a midbody diameter of 60 to 80 µm, prominent single lateral cuticular alae, and a large, centrally located and slightly compressed intestine, flanked on either side by smaller, dissimilar triangular excretory columns. Hematoxylin and eosin stain. Bar, 50.0 µm.