Walsh & Hoyt: Toxocara (Toxocariasis)

Toxocara canis is a roundworm that infects dogs and related mammals after they ingest viable eggs. Following ingestion, the eggs hatch in the small intestine of the host, following which most of the resultant larvae migrate tothe liver, lung, and trachea. They then are swallowed and mature in the lumen of the small intestine where they eventually reach a size of 712 cm in length and from which they eventually are shed in the feces. Other larvae migrate to the hosts muscles where they may remain dormant for months to years. During pregnancy, the larvae become active and infect the puppies both transplacentally and, following birth, transmammarily. The larvae subsequently mature within the small intestine of the puppies and produce eggs that are shed in the feces. Although the eggs are not infectious when passed in the feces, they are hardy, and they often remain viable for many months. Large numbers of viable eggs contaminate the environment because of the high prevalence of infection among dogs and the ability of the eggs to survive relatively harsh external conditions.