Question

Which larval stage of Ascaris is infective?

• A. First and fourth
• B. Second and third
• C. Second
• D. Third and fourth

Answer 1

The correct option is C Second

The first larval stage is formed by segmentation in gastrula and is called as noninfectious rhabditoid larva. Moulting of rhabditoid larva within eggshell forms second stage infectious rhabditoid larva or juvenile. Contaminated food or water transmits the infectious juvenile to host's small intestine wherein dissolution of egg shell by digestive juices set the second stage infectious juveniles free. From intestine, these are carried to liver via portal circulation and to heart via pulmonary circulation. Two successive moultings in lung alveoli release the third and fourth larval stage. The fourth larval stage makes their way from the respiratory path through the throat to small intestine again. Reaching intestine again includes their maturation into adult sexually mature worms. Thus, the correct answer is option C.