Toxocara species and Baylisascaris


  • 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.
  • Baylisascaris procyonis (raccoon roundworm worldwide, including the U.S.) has also been reported to cause VLM (mainly CNS forms, eosinophilic meningoencephalitis) and OLM.
  • Note: cutaneous larval migrans (CLM) is caused by several nematodes, most commonly hookworm (Ancylostoma braziliense).

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Last updated: February 5, 2023