Johns Hopkins ABX Guide
Toxocara species and Baylisascaris
MICROBIOLOGY
- Toxocara spp.
- Worldwide helminthic infection of humans, agent nematodes:
- Toxocara canis (dog roundworm)
- Toxocara cati (cat roundworm), less common
- Humans are infected as accidental hosts by ingesting eggs from contaminated soil [life cycle Fig. 1] by feces of infected dogs or cats.
- It usually occurs in overcrowded, poor living conditions with dogs or cats.
- Ingested eggs evolve to larval forms penetrating intestinal mucosa with subsequent spread to a variety of body organs (visceral larval migrans [VLM] and/or eyes, ocular larval migrans [OLM]) in arrested development, no ongoing production. Host inflammatory reactions produce symptoms as parasites die off.
- Human infection does not yield egg production; hence inspection of stool O&P is pointless.
- It usually occurs in overcrowded, poor living conditions with dogs or cats.
- Worldwide helminthic infection of humans, agent nematodes:
- Baylisascaris procyonis (raccoon roundworm worldwide, including the U.S.) has also been reported to cause VLM (mainly CNS forms, eosinophilic meningoencephalitis) and OLM.
- Life cycle [Fig 2]
- Note: cutaneous larval migrans (CLM) is caused by several nematodes, most commonly hookworm (Ancylostoma braziliense).
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Last updated: February 5, 2023
Citation
Auwaerter, Paul. "Toxocara Species and Baylisascaris." Johns Hopkins ABX Guide, The Johns Hopkins University, 2023. Johns Hopkins Guides, www.hopkinsguides.com/hopkins/view/Johns_Hopkins_ABX_Guide/540557/all/Toxocara_species_and__Baylisascaris.
Auwaerter P. Toxocara species and Baylisascaris. Johns Hopkins ABX Guide. The Johns Hopkins University; 2023. https://www.hopkinsguides.com/hopkins/view/Johns_Hopkins_ABX_Guide/540557/all/Toxocara_species_and__Baylisascaris. Accessed October 31, 2025.
Auwaerter, P. (2023). Toxocara species and Baylisascaris. In Johns Hopkins ABX Guide. The Johns Hopkins University. https://www.hopkinsguides.com/hopkins/view/Johns_Hopkins_ABX_Guide/540557/all/Toxocara_species_and__Baylisascaris
Auwaerter P. Toxocara Species and Baylisascaris [Internet]. In: Johns Hopkins ABX Guide. The Johns Hopkins University; 2023. [cited 2025 October 31]. Available from: https://www.hopkinsguides.com/hopkins/view/Johns_Hopkins_ABX_Guide/540557/all/Toxocara_species_and__Baylisascaris.
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