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Updated: Jul 2, 2026
Laparoscopic Technique for Serial Collection of Liver and Mesenteric Lymph Nodes in Macaques
Published on: May 2, 2017
Visceral and neural larva migrans in rhesus macaques
Alfonso S Gozalo1, Olga A Maximova, Marisa C StClaire
1Comparative Medicine Branch, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD, USA. gozaloa@niaid.nih.gov
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.
Insights
Rhesus macaques infected with Baylisascaris procyonis larvae showed no clinical signs, despite larvae found in lymph nodes and brains. This highlights covert Baylisascaris infections in non-human primates and evidence of the parasite in the southeastern US.
Area of Science:
- Veterinary Pathology
- Parasitology
- Primate Research
Background:
- Baylisascariasis, caused by Baylisascaris spp. larvae, is a known zoonotic disease.
- Raccoon roundworm (Baylisascaris procyonis) is a common cause of infection in animals and humans.
- Subclinical parasitic infections can be challenging to detect in research settings.
Purpose of the Study:
- To identify and characterize parasitic infections in rhesus macaques as incidental findings during a viral pathogenesis study.
- To determine the prevalence and morphology of ascarid larvae in rhesus macaques.
- To investigate the potential source and species of Baylisascaris in the study population.
Main Methods:
- Histological examination of tissues from euthanized rhesus macaques.
- Morphological analysis of nematode larvae found within granulomas.
- Epidemiological assessment of the macaques' origin and potential environmental exposure.
Main Results:
- Large ascarid larvae, consistent with Baylisascaris spp., were found in mesenteric and pancreatic lymph nodes of 13/21 macaques.
- Cerebral granulomas containing similar larvae were observed in 7/13 affected monkeys.
- Larval morphology included a midbody diameter of 60-80 µm and prominent lateral cuticular alae.
- The macaques' origin suggested Baylisascaris procyonis as the likely causative agent.
Conclusions:
- Rhesus macaques can harbor subclinical Baylisascaris infections.
- These findings provide evidence for the presence of Baylisascaris procyonis in the southeastern United States.
- The study underscores the importance of considering parasitic infections in non-human primate research, even in the absence of clinical signs.
