A woman who had measles as a child gets the disease again after her younger brother contracts the disease. This probably occure because od a defect in which mechanism?

A.viral mutation
B. Artificial acquired immunity
C. Natural acquired immunity
D. Passive immunity

Those who have measles develop a natural acquired immunity. A defect in this could lead to another infection.

, I searched Google under the key words "measles immunity" to get these possible sources:

http://science.education.nih.gov/supplements/nih1/diseases/activities/activity5_measles-database.htm#4
http://www.medscape.com/viewarticle/408098

In the future, you can find the information you desire more quickly, if you use appropriate key words to do your own search. Also see http://hanlib.sou.edu/searchtools/.

I hope this helps. Thanks for asking.