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.
• 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).