Coloured scanning electron micrograph (SEM) of the posterior end and general body surface of a dog roundworm (Toxocara canis). T. canis is the cause of toxocariasis (visceral larva migrans) in humans. It is a parasitic infection caused by oral contact with material contaminated by eggs in dog faeces. Ingested eggs hatch into larvae in the intestines, then migrate through the tissues to organs such as the liver, lungs, brain and eyes. The migrating larvae may cause anything from mild malaise to asthma, seizures, pneumonia and blindness. Magnification: x7 when shortest axis printed at 25 millimetres.