Baylisascaris Larva Migrans

Circular 1412
Edited by: Rachel C. Abbott and Charles van Riper III



Baylisascaris procyonis, the common raccoon roundworm, is the most commonly recognized cause of clinical larva migrans (LM) in animals, a condition in which an immature parasitic worm or larva migrates in a host animal’s tissues, causing obvious disease. Infection with B. procyonis is best known as a cause of fatal or severe neurologic disease that results when the larvae invade the brain, the spinal cord, or both; this condition is known as neural larva migrans (NLM). Baylisascariasis is a zoonotic disease, that is, one that is transmissible from animals to humans. In humans, B. procyonis can cause damaging visceral (VLM), ocular (OLM), and neural larva migrans. Due to the ubiquity of infected raccoons around humans, there is considerable human exposure and risk of infection with this parasite. The remarkable disease-producing capability of B. procyonis in animals and humans is one of the most significant aspects of the biology of ascarids (large roundworms) to come to light in recent years. Infection with B. procyonis has important health implications for a wide variety of free-ranging and captive wildlife, zoo animals, domestic animals, as well as human beings, on both an individual and population level. This report, eighth in the series of U.S. Geological Survey Circulars on zoonotic diseases, will help us to better understand the routes of Baylisascaris procyonis infections and how best to adequately monitor this zoonotic disease.

Suggested Citation

Kazacos, K.R., 2016, Baylisascaris Larva Migrans: U.S. Geological Survey Circular 1412, 122 p., 3 appendixes,

ISSN: 2330-5703 (online)

ISSN: 1067-084X (print)

Table of Contents

  • Foreword
  • Acknowledgments
  • Overview
  • Background
  • Causative Agent 
  • Geographic Distribution
  • Patterns and Trends
  • Species Susceptibility 
  • Obtaining a Diagnosis
  • Disease Ecology
  • Points to Ponder
  • Disease Prevention and Control 
  • References Cited
  • Glossary
  • Appendix 1. Common and scientific names of animals cited
  • Appendix 2. Cases of Baylisascaris neural larva migrans in pets
  • Appendix 3. Cases of  Baylisascaris neural larva migrans in animal facilities 
Publication type Report
Publication Subtype USGS Numbered Series
Title Baylisascaris Larva Migrans
Series title Circular
Series number 1412
DOI 10.3133/cir1412
Year Published 2016
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) National Wildlife Health Center
Description x, 122 p.
Online Only (Y/N) N
Additional Online Files (Y/N) N
Google Analytic Metrics Metrics page
Additional publication details