Zoonotic concern: Baylisascaris procyonis

Key Points

  • Baylisascaris procyonis is commonly known as the raccoon roundworm.
  • This nematode is widespread in raccoons in North America.
  • Adult female worms live in the raccoon intestine, depositing eggs that are shed in feces.
  • Raccoon latrines are communal defecation sites that can concentrate B. procyonis eggs.
  • Baylisascaris procyonis is a zoonotic parasite. Humans as well as a wide variety of other mammals and birds can serve as paratenic or accidental hosts of B. procyonis.
  • When infective eggs are ingested by paratenic hosts, larvae can migrate through internal organs (visceral larva migrans), the brain (neural larva migrans), and eye (ocular larva migrans), causing serious health issues.
  • Dogs are an alternate definitive host as well as a possible paratenic host. Therefore infections in dogs can result in either patent adult worms in the intestinal tract or larval tissue migration.
  • Most human cases have been documented in young children, especially those 2 years and younger, due to a higher risk of ingesting B. procyonis eggs when compared to adults.
  • Individuals with occupational exposure to raccoons or their feces are also at risk for Baylisascaris infection
  • The public health risk of B. procyonis can be reduced by increasing awareness of this pathogen, particularly in individuals and institutions caring for young children as well as animal care workers.
  • Minimize direct exposure to raccoon feces or contaminated materials through avoidance, personal protective equipment, proper cleaning and disinfection, and hand hygiene.
  • Baylisascaris eggs are extremely hardy, but they can be killed using various forms of heat.
  • Raccoon feces can also be physically removed before eggs become infective, making it possible to decontaminate areas and materials.

This zoonotic concern article reviews Baylisascaris procyonis or the raccoon roundworm. Baylisascaris procyonis exhibits a typical ascarid life cycle with adult female worms in the raccoon intestine depositing eggs that are shed in the raccoon feces. Humans can serve as paratenic or accidental hosts of B. procyonis, however more than 150 species of free-ranging and captive wildlife, zoo animals, and domestic animals have also been afflicted. When infective eggs are ingested by paratenic hosts, Baylisascaris larvae can migrate through the brain, eye, and other organs, causing serious health issues. Who is most at risk? What strategies can be implemented . . .

To continue you need to be a LafeberVet.com member. (Français), (Español)

Pour continuer, vous devez être un membre LafeberVet.com

Para continuar, debe ser miembro de LafeberVet.com

Already a LafeberVet Member?

Please Login


1. Bauer C, Gey A. Efficacy of six anthelmintics against luminal stages of Baylisascaris procyonis in naturally infected raccoons (Procyon lotor). Vet Parasitol. 1995;60(1-2):155-9. doi: 10.1016/0304-4017(94)00774-7. PMID: 8644451.

1b. Baldi M, Alvarado G, Smith S, et al. Baylisascaris procyonis parasites in raccoons, Costa Rica, 2014. Emerg Infect Dis. 2016;22(8):1502-3. doi: 10.3201/eid2208.151627. PMID: 27433741; PMCID: PMC4982188.

2. Bezerra-Santos MA, Mendoza-Roldan JA, Thompson RCA, Dantas-Torres F, Otranto D. Illegal wildlife trade: a gateway to zoonotic infectious diseases. Trends Parasitol. 2021;37(3):181-184. doi: 10.1016/j.pt.2020.12.005. Epub 2021 Jan 13. PMID: 33454218.

3. Blizzard EL, Yabsley MJ, Beck MF, Harsch S. Geographic expansion of Baylisascaris procyonis roundworms, Florida, USA. Emerg Infect Dis. 2010;16(11):1803-4. doi: 10.3201/eid1611.100549. PMID: 21029553; PMCID: PMC3294519.

4. Bowman DD. Georgis’ Parasitology For Veterinarians, 9th ed. St. Louis, MO: Saunders Elsevier; 2009: 207-208.

5. Center for Disease Control and Prevention: Parasites – Baylisascaris infection: Prevention & control. Sep 28, 2018. CDC web site. Available at https://www.cdc.gov/dpdx/baylisascariasis/index.html. Accessed January 9, 2022.

6. Center for Disease Control and Prevention: DPDx – Laboratory Identification of Parasites of Public Health Concern. Baylisascariasis. June 13, 2019. CDC web site. Available at
https://www.cdc.gov/parasites/baylisascaris/prevent.html. Accessed January 9, 2022.

7. Davidson RK, Øines Ø, Hamnes IS, Schulze JE. Illegal wildlife imports more than just animals–Baylisascaris procyonis in raccoons (Procyon lotor) in Norway. J Wildl Dis. 2013;49(4):986-90. doi: 10.7589/2012-06-154. PMID: 24502726.

8. Desprez I, Yabsley MJ, Fogelson SB, et al. Baylisascaris procyonis larva migrans in two captive North American beavers (Castor canadensis). J Zoo Wildl Med. 2017; 48(1):232-236. doi: 10.1638/2016-0102.1. PMID: 28363038.

9. Dunbar M, Lu S, Chin B, et al. Baylisascariasis: A young boy with neural larva migrans due to the emerging raccoon round worm. Ann Clin Transl Neurol. 2018;6(2):397-400. doi: 10.1002/acn3.694. PMID: 30847373; PMCID: PMC6389752.

10. Duscher GG, Frantz AC, Kuebber-Heiss A, Fuehrer HP, Heddergott M. A potential zoonotic threat: First detection of Baylisascaris procyonis in a wild raccoon from Austria. Transbound Emerg Dis. 2021;68(6):3034-3037. doi: 10.1111/tbed.13963. Epub 2021 Jan 7. PMID: 33345448.

11. French SK, Pearl DL, Peregrine AS, Jardine CM. Spatio-temporal clustering of Baylisascaris procyonis, a zoonotic parasite, in raccoons across different landscapes in southern Ontario. Spat Spatiotemporal Epidemiol. 2020;35:100371. doi: 10.1016/j.sste.2020.100371. Epub 2020 Aug 5. PMID: 33138952.

12. French SK, Pearl DL, Peregrine AS, Jardine CM. Baylisascaris procyonis infection in raccoons: A review of demographic and environmental factors influencing parasite carriage. Vet Parasitol Reg Stud Reports. 2019;16:100275. doi: 10.1016/j.vprsr.2019.100275. Epub 2019 Feb 21. PMID: 31027589.

13. French SK, Pearl DL, Shirose L, Peregrine AS, Jardine CM. Demographic and environmental factors associated with Baylisascaris procyonis infection of raccoons (Procyon lotor) in Ontario, Canada. J Wildl Dis. 2020;56(2):328-337. Epub 2019 Oct 28. PMID: 31658429.

13b. Graeff-Teixeira C, Morassutti AL, Kazacos KR. Update on baylisascariasis, a highly pathogenic zoonotic infection. Clin Microbiol Rev. 2016;29(2):375-99. doi: 10.1128/CMR.00044-15. PMID: 26960940; PMCID: PMC4786883.

14. Hazlett M, Cai HY, Sparling S, You Q. Neurologic Baylisascaris procyonis infection in a young dog. Can Vet J. 2018;59(12):1325-1328. PMID: 30532291; PMCID: PMC6237265.

15. Heddergott M, Steinbach P, Schwarz S, et al. Geographic distribution of raccoon roundworm, Baylisascaris procyonis, Germany and Luxembourg. Emerg Infect Dis. 2020;26(4):821-823. doi: 10.3201/eid2604.191670. PMID: 32187005; PMCID: PMC7101099.

16. Heller HB, Arnold S, Dreyfus JL. Baylisascaris procyonis central nervous system infection in a four-month-old Gordon setter dog. J Am Anim Hosp Assoc. 2019;55(3):e55301. doi: 10.5326/JAAHA-MS-6667. Epub 2019 Mar 14. PMID: 30870604.

17. Hung T, Neafie RC, Mackenzie IR. Baylisascaris procyonis infection in elderly person, British Columbia, Canada. Emerg Infect Dis. 2012;18(2):341-2. doi: 10.3201/eid1802.111046. PMID: 22305101; PMCID: PMC3310454.

18. Kaplan RM. Biology, epidemiology, diagnosis, and management of anthelmintic resistance in gastrointestinal nematodes of livestock. Vet Clin North Am Food Anim Pract. 2020;36(1):17-30. doi: 10.1016/j.cvfa.2019.12.001. PMID: 32029182.

19. Kawakami V, Casto A, Natarajan N, et al. Notes from the field: Baylisascaris procyonis encephalomyelitis in a toddler – King County, Washington, 2017. MMWR Morb Mortal Wkly Rep. 2018;67(2):79-80. doi: 10.15585/mmwr.mm6702a6. PMID: 29346337; PMCID: PMC5772797.

20. Kazacos KR. 2016, Baylisascaris Larva Migrans: U.S. Geological Survey Circular 1412. 2016. doi: 10.3133/cir1412. Available at https://pubs.usgs.gov/circ/1412/cir1412.pdf. Accessed Jan 9, 2022.

21. Johnson D. Coatimundi, kinkajou, and raccoon care. Proc Annu Conf Atlantic Coast Veterinary Conference 2006.

22. Louis MM, Minter LJ, Flowers JR, Stoskopf MK, Kennedy-Stoskopf S. Raccoon roundworm prevalence (Baylisascaris procyonis) at the North Carolina Zoo, USA. PeerJ. 2020;8:e9426. doi: 10.7717/peerj.9426. PMID: 32742774; PMCID: PMC7377244.

23. Maas M, Tatem-Dokter R, Rijks JM, et al. Population genetics, invasion pathways and public health risks of the raccoon and its roundworm Baylisascaris procyonis in northwestern Europe. Transbound Emerg Dis. 2021. doi: 10.1111/tbed.14218. Epub ahead of print. PMID: 34227236.

24. Meteyer CU, Rogall GM. Fact Sheet 2017-3077: Information to prevent human exposure to disease agents associated with wildlife—U.S. Geological Survey Circulars on Zoonotic Disease. March 2018. USGS web site. Available at https://pubs.usgs.gov/fs/2017/3077/fs20173077.pdf. Accessed January 9, 2022.

25. Muganda GN, Akagi NE, Fagbemi OD, Chusid MJ, Nelson AM. Rapid therapeutic response of eosinophilic meningoencephalitis in a toddler with Baylisascaris procyonis infection. WMJ. 2018;117(3):130-132. PMID: 30193023.

26. Ogdee JL, Henke SE, Wester DB, Fedynich AM. Assessing potential environmental contamination by Baylisascaris procyonis eggs from infected raccoons in southern Texas. Vector Borne Zoonotic Dis. 2017;17(3):185-189. doi: 10.1089/vbz.2016.2011. Epub 2016 Nov 14. PMID: 27841964.

27. Pope T, Henke SE, Wester DB, Rideout-Hanzak S, Hilton CD. Effect of prescribed fire on the viability of Baylisascaris procyonis eggs. J Wildl Dis. 2021;57(1):94-103. doi: 10.7589/JWD-D-20-00078. PMID: 33635980.

28. Rainwater KL, Marchese K, Slavinski S, et al. Health survey of free-ranging raccoons (Procyon lotor) in Central Park, New York, New York, USA: Implications for human and domestic animal health. J Wildl Dis. 2017;53(2):272-284. doi: 10.7589/2016-05-096. Epub 2017 Jan 30. PMID: 28135131.

29. Rentería-Solís Z, Birka S, Schmäschke R, Król N, Obiegala A. First detection of Baylisascaris procyonis in wild raccoons (Procyon lotor) from Leipzig, Saxony, Eastern Germany. Parasitol Res. 2018;117(10):3289-3292. doi: 10.1007/s00436-018-5988-2. Epub 2018 Jun 27. PMID: 29951707.

29b. Sapp SGH, Elsemore DA, Hanna R, Yabsley MJ. Experimental comparison of Baylisascaris procyonis definitive host competence between domestic dogs and raccoons (Procyon lotor). Parasitology. 2020;147(12):1344-1351. doi: 10.1017/S0031182020001122. Epub 2020 Jul 14. PMID: 32660656.

30. Sapp SGH, Murray B, Hoover ER, Green GT, Yabsley MJ. Raccoon roundworm (Baylisascaris procyonis) as an occupational hazard: 2. Use of personal protective equipment and infection control practices among raccoon rehabilitators. Zoonoses Public Health. 2018;65(5):490-500. doi: 10.1111/zph.12454. Epub 2018 Mar 30. PMID: 29603886.

31. Sapp SGH, Murray BA, Hoover ER, Green GT, Yabsley MJ. Raccoon roundworm (Baylisascaris procyonis) as an occupational hazard: 1. Knowledge of B. procyonis and attitudes towards it and other zoonoses among wildlife rehabilitators. Zoonoses Public Health. 2018;65(1):e130-e142. doi: 10.1111/zph.12421. Epub 2017 Nov 10. PMID: 29124901.

32. Sapp SG, Rascoe LN, Wilkins PP, et al. Baylisascaris procyonis roundworm seroprevalence among wildlife rehabilitators, United States and Canada, 2012-2015. Emerg Infect Dis. 2016;22(12):2128-2131. doi: 10.3201/eid2212.160467. PMID: 27869612; PMCID: PMC5189140.

33. Shafir SC, Sorvillo FJ, Sorvillo T, Eberhard ML. Viability of Baylisascaris procyonis eggs. Emerg Infect Dis. 2011;17(7):1293-5. doi: 10.3201/eid1707.101774. PMID: 21762591; PMCID: PMC3381372.

34. Shafir SC, Wang W, Sorvillo FJ, et al. Thermal death point of Baylisascaris procyonis eggs. Emerg Infect Dis. 2007;13(1):172-3. doi: 10.3201/eid1301.060966. PMID: 17370540; PMCID: PMC2725829.

35. 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 Morb Mortal Wkly Rep. 2016;65(35):930-3. doi: 10.15585/mmwr.mm6535a2. PMID: 27608169.

36. Smyser TJ, Johnson SR, Stallard MD, et al. Evaluation of anthelmintic fishmeal polymer baits for the control of Baylisascaris procyonis in free-ranging raccoons (Procyon lotor). J Wildl Dis. 2015;51(3):640-50. doi: 10.7589/2014-09-236. Epub 2015 May 14. PMID: 25973621.

37. Straif-Bourgeois S, Cloherty E, Balsamo G, Gee L, Riegel C. Prevalence of Baylisascaris procyonis in raccoons trapped in New Orleans, Louisiana, 2014-2017. Vector Borne Zoonotic Dis. 2020;20(1):22-26. doi: 10.1089/vbz.2019.2498. Epub 2019 Aug 15. PMID: 31414972.

38. Thornton GL, French SK, Peregrine AS, Jardine CM. Prevalence of Baylisascaris procyonis in raccoon latrines in southern Ontario, Canada. Vet Parasitol Reg Stud Reports. 2020;20:100392. doi: 10.1016/j.vprsr.2020.100392. Epub 2020 Feb 22. PMID: 32448536.

39. Vincent EC, Ruder MG, Yabsley MJ, et al. A Baylisascaris outbreak in fox squirrels (Sciurus niger) and subsequent detection of Francisella tularensis in Kansas, USA. J Wildl Dis. 2020;56(2):457-461. Epub 2019 Nov 21. PMID: 31750777.

40. Weinstein SB. Introduced rats and an endemic roundworm: does Rattus rattus contribute to Baylisascaris procyonis transmission in California? J Parasitol. 2017;103(6):677-682. doi: 10.1645/17-83. Epub 2017 Jul 21. PMID: 28732456.

41. Weinstein SB. Baylisascaris procyonis demography and egg production in a California raccoon population. J Parasitol. 2016;102(6):622-628. doi: 10.1645/15-747. Epub 2016 Aug 24. PMID: 27556367.

42. Weinstein SB, Lake CM, Chastain HM, et al. Seroprevalence of Baylisascaris procyonis infection among humans, Santa Barbara county, California, USA, 2014-2016. Emerg Infect Dis. 2017;23(8):1397-1399. doi: 10.3201/eid2308.170222. PMID: 28726612; PMCID: PMC5547801.

43. Yabsley MJ, Sapp SGH. Prevalence of Baylisascaris in domestic dog coprological examinations in the United States, 2013-2016. Vet Parasitol Reg Stud Reports. 2017;9:65-69. doi: 10.1016/j.vprsr.2017.05.003. Epub 2017 May 20. PMID: 31014845.

44. Zajac AM, Conboy GA. Veterinary Clinical Parasitology, 8th ed. Ames, Iowa: Wiley-Blackwell; 2012: 58-59.

45. Zimmerman DM, Dangoudoubiyam S, Kazacos KR. Serological diagnosis of Baylisascaris procyonis in primates using a human ELISA test. J Zoo Wildl Med. 2019 ;50(2):414-420. doi: 10.1638/2017-0207. PMID: 31260208.


Further reading

Camp LE, Radke MR, Shihabi DM, et al. Molecular phylogenetics and species-level systematics of Baylisascaris. Int J Parasitol Parasites Wildl. 2018 Oct 22;7(3):450-462. doi: 10.1016/j.ijppaw.2018.09.010. PMID: 30568876; PMCID: PMC6275171.

Fox AS, Kazacos KR, Gould NS, et al. Fatal eosinophilic meningoencephalitis and visceral larva migrans caused by the raccoon ascarid Baylisascaris procyonis. N Engl J Med. 1985;312(25):1619-23. doi: 10.1056/NEJM198506203122507. PMID: 4039793.

Gavin PJ, Kazacos KR, Shulman ST. Baylisascariasis. Clin Microbiol Rev. 2005;18(4):703-18. doi: 10.1128/CMR.18.4.703-718.2005. PMID: 16223954; PMCID: PMC1265913.

Huff DS, Neafie RC, Binder MJ, et al. Case 4. The first fatal Baylisascaris infection in humans: an infant with eosinophilic meningoencephalitis. Pediatr Pathol. 1984;2(3):345-52. doi: 10.3109/15513818409022268. PMID: 6542658.

Kazacos KR. Baylisascaris procyonis and related species. In: Samuels WM, Pybus MJ, Kocans AA (eds). Parasitic Diseases of Wild Mammals, 2nd ed. Ames (IA):Iowa State University Press; 2001. Pp. 301-341.

Moro KK, Abah AE. Epizootiology of zoonotic parasites of dogs in Abua area of Rivers State, Nigeria. Vet Anim Sci. 2018 Dec 11;7:100045. doi: 10.1016/j.vas.2018.100045. PMID: 32734067; PMCID: PMC7386753.

Romeo C, Cafiso A, Fesce E, et al. Lost and found: Helminths infecting invasive raccoons introduced to Italy. Parasitol Int. 2021 Aug;83:102354. doi: 10.1016/j.parint.2021.102354. Epub 2021 Apr 16. PMID: 33872791.

Umhang G, Duchamp C, Boucher JM, et al. Detection of DNA from the zoonotic raccoon roundworm Baylisascaris procyonis in a French wolf. Parasitol Int. 2020 Oct;78:102155. doi: 10.1016/j.parint.2020.102155. Epub 2020 Jun 6. PMID: 32512048.

To cite this page:

Pollock C. Zoonotic concern: Baylisascaris procyonis. January 18, 2022. LafeberVet Web site. Available at https://lafeber.com/vet/zoonotic-concern-baylisascaris-procyonis/