What is the infective stage of Ascaris lumbricoides?

The infective stage of Ascaris lumbricoides is the embryonated egg. This parasite, which is a common roundworm in humans, has a complex life cycle that begins when an individual ingests the infective eggs from contaminated food or soil.

During the development process within the environment, these eggs undergo a maturation phase to become embryonated, which usually takes several weeks under suitable conditions. Mature embryonated eggs are resilient and can survive for extended periods outside the host. Once ingested, they hatch in the intestines, releasing larvae that penetrate the intestinal wall, enter the bloodstream, and migrate to the lungs before they are ultimately swallowed back into the gastrointestinal tract to mature into adult worms.

In contrast, adult worms, larvae, and fertilized eggs are part of different stages in the life cycle and do not represent the stage that leads directly to infection. Adult worms are the stage that causes symptoms in the host, while unfertilized or non-embryonated eggs do not pose an infection risk until they develop into the infective embryonated form. Understanding this life cycle is crucial in recognizing how the transmission of Ascaris lumbricoides occurs in populations.